Reactions of group IV metal atoms with water molecules. Matrix isolation FTIR and theoretical studies

Article abstract of DOI:10.1021/ja0020658

Laser-ablated group IV metal atoms have been co-deposited at 11 K with water molecules in excess argon. The metal atoms reacted with water to form the insertion product HMOH and H₂M(OH)₂ (M = Ti, Zr, Hf) molecules spontaneously. Phot

Full text of DOI:10.1021/ja0020658

10680
J. Am. Chem. Soc. 2000, 122, 10680-10688
Reactions of Group IV Metal Atoms with Water Molecules. Matrix
Isolation FTIR and Theoretical Studies
Mingfei Zhou,* Luning Zhang, Jian Dong, and Qizong Qin
Contribution from the Laser Chemistry Institute, Department of Chemistry, Fudan UniVersity,
Shanghai, People’s Republic of China
ReceiVed June 9, 2000
Abstract: Laser-ablated group IV metal atoms have been co-deposited at 11 K with water molecules in excess
argon. The metal atoms reacted with water to form the insertion product HMOH and H2M(OH)2 (M ) Ti, Zr,
Hf) molecules spontaneously. Photolysis of the HTiOH species produced the H2TiO molecule as well as the
TiO monoxide. In the cases of Zr and Hf, however, the H2ZrO and H2HfO molecules were produced on
annealing, and the H2 elimination process was not observed on photolysis. In addition, the HMO species were
also observed and identified. The aforementioned species were identified via isotopic substitutions as well as
theoretical frequency calculations. Qualitative analysis of the possible reaction paths leading to the observed
products is proposed.
Introduction
reactivity depending on the spin, electron configuration, and
spin-orbital level has been discussed. These results showed
that earlier transition metal cations (Sc+, Ti+, and V+) are more
reactive than their oxides, and the formation of the low-lying
state MO+ + H2 is the only exothermic process.7-9,17,18 It is of
great interest to compare the chemistry of transition metal
cations and neutral atoms.
Recently, we have performed a matrix isolation FTIR and
theoretical study of reactions of laser-ablated Sc with water.20
The difference between laser-ablated and thermal evaporated
Sc atom reactions is the observation of HScO and ScOH
molecules with laser ablation. In this paper, we present a
combined matrix isolation FTIR spectroscopic and theoretical
investigation on the reactions of laser-ablated group IV metal
atoms with water molecules.
The interactions of transition metals with small molecules
are of chemical interest as such reactions may play important
roles in catalytic and chemisorption processes. Recent studies
of transition metal atoms with small molecules have provided
insight into the activation of bonds such as H-H,1 C-O,2 and
N-O.3 There are several reports on the reactions of transition
metal atoms with water molecules. Liu and Parson reported that
atomic Sc reacted with water to give ScO in the gas phase.4
Using the matrix isolation infrared absorption method, Kauffman
et al. showed that thermal Sc, Ti, and V atoms could react with
water to form the insertion products spontaneously, while the
metal monoxides were formed on photolysis, but later transition
metal atoms formed adducts with water, which were rearranged
to the insertion molecules on photolysis.5,6 To our knowledge,
there is no report on the reactions of the second- and third-row
transition metals with water.
Experimental and Theoretical Methods
The reactions of transition metal cations and water have
The experimental setup for pulsed laser ablation and matrix infra-
red spectroscopic investigation has been described previously21 and
is similar to the technique employed by the Andrews group.22 The
1064-nm Nd:YAG laser fundamental (Spectra Physics, DCR 150, 20
Hz repetition rate and 8 ns pulse width) was focused onto the rotating
metal target through a hole in a CsI window, and the ablated metal
atoms were co-deposited with H2O in excess argon onto a 11 K CsI
window, which was mounted on a cold tip of a closed-cycle helium
refrigerator (Air Products, Model CSW202), for 1 h at a rate of
received much attention recently. The M+ + H2O f MO+
+
H2 and its reverse reactions have been studied both experi-
mentally7-11 and theoretically.12-19 The different gas-phase
* Corresponding author. E-mail: mfzhou@srcap.stc.sh.cn. Fax: 0086-
21-65102777.
(1) See, for example: Chertihin, G. V.; Andrews, L. J. Am. Chem. Soc.
1994, 116, 8322; 1995, 117, 6402.
(2) See, for example: Zhou, M. F.; Andrews, L. J. Am. Chem. Soc. 1998,
120, 13230; 2000, 122, 1531.
(3) See, for example: Kushto, G. P.; Zhou, M. F.; Andrews, L.;
Bauschlicher, C. W., Jr. J. Phys. Chem. A 1999, 103, 1115. Zhou, M. F.;
Andrews, L. J. Phys. Chem. A 1998, 102, 7452.
(4) Liu, K.; Parson, J. M. J. Chem. Phys. 1978, 68, 1794.
(5) Kauffman, J. W.; Hauge, R. H.; Margrave, J. L. J. Phys. Chem. 1985,
89, 3541.
(6) Kauffman, J. W.; Hauge, R. H.; Margrave, J. L. J. Phys. Chem. 1985,
89, 3547.
(7) Clemmer, D. E.; Aristov, N.; Armentrout, P. B. J. Phys. Chem. 1993,
97, 544.
(8) Chen, Y. M.; Clemmer, D. E.; Armentrout, P. B. J. Phys. Chem.
1994, 98, 11490.
(9) Guo, B. C.; Kerns, K. P.; Castleman, A. W. J. Phys. Chem. 1992,
96, 4879.
(10) Ryan, M. F.; Fiedler, A.; Schroder, D.; Schwarz, H. J. Am. Chem.
Soc. 1995, 117, 2033.
(11) Schroder, D.; Fiedler, A.; Ryan, M. F.; Schwarz, H. J. Phys. Chem.
1994, 98, 68.
(12) Clemmer, D. E.; Chen, Y. M.; Khan, F. A.; Armentrout, P. B. J.
Phys. Chem. 1994, 98, 6522.
(13) Tilson, J. L.; Harrison, J. F. J. Phys. Chem. 1991, 95, 5097.
(14) Fiedler, A.; Schroder, D.; Shaik, S.; Schwarz, H. J. Am. Chem. Soc.
1994, 116, 10734.
(15) Danovich, D.; Shaik, S. J. Am. Chem. Soc. 1997, 119, 1773.
(16) Ye, S. THEOCHEM 1997, 417, 157.
(17) Irigoras, A.; Fowler, J. E.; Ugalde, J. M. J. Phys. Chem. A 1998,
102, 293.
(18) Irigoras, A.; Fowler, J. E.; Ugalde, J. M. J. Am. Chem. Soc. 1999,
121, 574.
(19) Irigoras, A.; Fowler, J. E.; Ugalde, J. M. J. Am. Chem. Soc. 1999,
121, 8549.
(20) Zhang, L. N.; Dong, J.; Zhou, M. F. J. Phys. Chem. A, to be
published.
(21) Chen, M. H.; Wang, X. F.; Zhang, L. N.; Yu, M.; Qin, Q. Z. Chem.
Phys. 1999, 242, 81.
(22) Burkholder, T. R.; Andrews, L. J. Chem. Phys. 1991, 95, 8697.
10.1021/ja0020658 CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/14/2000

Reactions of Group IV Metal Atoms with Water Molecules
J. Am. Chem. Soc., Vol. 122, No. 43, 2000 10681
Figure 1. Infrared spectra in the 1700-1460 and 1030-920 cm-1 regions from co-deposition of laser-ablated Ti with 0.2% water in argon: (a)
1 h sample deposition, (b) 25 K annealing, (c) 20 min broadband photolysis, and (d) annealing to 30 K.
2-4 mmol/h. Typically, 5-10 mJ/pulse laser power was used. H2O,
H218O(96%18O), and D2O were subjected to several freeze-pump-
thaw cycles before use. Infrared spectra were recorded on a Bruker
IFS113V spectrometer at 0.5 cm-1 resolution using a DTGS detector.
Matrix samples were annealed at different temperatures, and selected
samples were subjected to broadband photolysis using a high-pressure
mercury lamp.
Quantum chemical calculations were performed using the Gaussian
98 program.23 The three-parameter hybrid functional according to Becke
with additional correlation corrections due to Lee, Yang, and Parr was
utilized (B3LYP).24,25 Recent calculations have shown that this hybrid
functional can provide accurate results for the geometries and vibrational
frequencies for transition metal-containing compounds.17-19,26,27 The
6-311++G(d,p) basis sets were used for H and O atoms, the all-electron
basis sets of Wachter-Hay as modified by Gaussian were used for Ti
atom, and the Los Alamos ECP plus DZ basis sets were used for Zr
and Hf atoms.28-30 These ECPs incorporate Darwin relativistic effects
into the potentials. Recent reports have shown that density functional
theoretical calculations using similar basis sets on O or C atoms and
effective core potentials on metal atoms predicted the geometries,
vibrational frequencies, and energetics of second- and third-row
transition metal compounds reasonably well.31 Reactants, various
Table 1. Infrared Absorptions (cm-1) from Co-deposition of
Laser-Ablated Ti with Water in Excess Argon
H2O
D2O
H218O
assignment
1688.3
1666.2
1646.8
1634.3
1611.9
1549.1
1483.3
1341.8
1015.8
1013.0
1010.5
1008.0
1005.3
990.3
974.2
971.5
968.8
966.3
963.5
933.4
844.3
805.5
1687.3
1665.8
1645.4
H2Ti(OH)2 sym-TiH2
H2Ti(OH)2 asym-TiH2
H2TiO sym-TiH2
HTi(OH)3 Ti-H
H2TiO asym-TiH2
HTiOH Ti-H
HTiO Ti-H
1168.2
1611.3
1549.1
1482.8
1071.1
978.3
HTiO- Ti-H
H246TiO
H247TiO
1009.6
990.3
967.9
931.1
968.8
948.4
928.1
895.8
H248TiO Ti-O
H249TiO
H250TiO
TiO
H46TiO
H47TiO
H48TiO Ti-O
H49TiO
H50TiO
HTiO- Ti-O
HTi(OH)3 Ti-OH
H2Ti(OH)2 asym-Ti-(OH)2
H2Ti(OH)2 symm-Ti-(OH)2
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-
Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe,
M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.;
Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian
98, Revision A.7; Gaussian, Inc.: Pittsburgh, PA, 1998.
775.5
possible transition states, intermediates, and products were optimized.
The vibrational frequencies were calculated with analytic second
derivatives, and zero-point vibrational energies (ZPVE) were derived.
Single-point CCSD(t) calculations have been carried out at the B3LYP
equilibrium geometries with the same basis sets for selected systems.
Results and Discussion
Infrared Spectra. Experiments were done with different
water concentrations ranging from 0.2% to 0.5% in argon.
Typical infrared spectra for the reactions of laser-ablated Ti,
Zr, and Hf atoms with 0.2% water molecules in argon in the
metal hydride and metal oxide stretching vibrational frequency
regions are shown in Figures 1-3, respectively, and the product
absorptions are listed in Tables 1-3. The stepwise annealing
(24) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(25) Lee, C.; Yang, E.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(26) Bauschlicher, C. W., Jr.; Ricca, A.; Partridge, H.; Langhoff, S. R.
In Recent AdVances in Density Functional Theory; Chong, D.P., Ed.; World
Scientific Publishing: Singapore, 1997; Part II.
(27) Bytheway, I.; Wong, M. W. Chem. Phys. Lett. 1998, 282, 219.
(28) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639.
Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980,
72, 650.
(29) Wachter, J. H. J. Chem. Phys. 1970, 52, 1033. Hay, P. J. J. Chem.
Phys. 1977, 66, 4377.
(30) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(31) See, for example: Andrews, L.; Zhou, M. F.; Chertihin, G. V.;
Bauschlicher, C. W., Jr. J. Phys. Chem. A 1999, 103, 6525. Zhou, M. F.;
Andrews, L. J. Phys. Chem. A 1999, 103, 7763.

10682 J. Am. Chem. Soc., Vol. 122, No. 43, 2000
Zhou et al.
Figure 2. Infrared spectra in the 1650-1520 and 970-890 cm-1 regions from co-deposition of laser-ablated Zr with 0.2% water in argon: (a)
1 h sample deposition, (b) 25 K annealing, (c) 20 min broadband photolysis, and (d) annealing to 30 K.
Figure 3. Infrared spectra in the 1685-1600 and 970-890 cm-1 regions from co-deposition of laser-ablated Hf with 0.2% water in argon: (a)
1 h sample deposition, (b) 25 K annealing, (c) 20 min broadband photolysis, and (d) annealing to 30 K.
and photolysis behavior of these product absorptions is also
shown in the figures and will be discussed below. D2O and
H218O samples were employed for product identification through
isotopic shift and splitting, and the representative spectra with
mixed H2O + HDO + D2O and H216O + H218O in selected
regions are shown in Figures 4-7, respectively.
Calculations were done on two [M,O,H] isomers, namely
HMO and MOH (M ) Ti, Zr, Hf). The calculated geometric
parameters and relative stability are shown in Figure 8, and the
vibrational frequencies and intensities are listed in Table 6. All
three HMO molecules in this family were predicted to have
doublet ground states with bent geometry and are more stable
than the MOH isomers.
Calculations were also done for two isomers of MH2O on
both singlet and triplet potential energy surfaces, namely, the
inserted HMOH molecules and the H2MO molecules. The
Calculation Results. The energy differences between the 3F
ground state and the 1D first singlet excited state of metal atoms
are listed in Table 4. The B3LYP results are slightly overesti-
mated, and the CCSD(t) results are closer to the experimental
values.32 Calculation results on monoxides are listed in Table
5. CCSD(t) calculations predicted the ground states correctly,
but B3LYP calculations predicted the 3∆ state to be the ground
state for ZrO, which is in error.33
(32) Moore, C. E. Atomic Energy LeVels; National Bureau of Stan-
dards: Washington, DC, 1959.
(33) Hammer, P. D.; Davis, S. P. Astrophys. J. 1980, 237, L51. Langhoff,
S. R.; Bauschlicher, C. W., Jr. J. Chem. Phys. 1988, 89, 2160.

Reactions of Group IV Metal Atoms with Water Molecules
J. Am. Chem. Soc., Vol. 122, No. 43, 2000 10683
Table 2. Infrared Absorptions (cm-1) from Co-deposition of
Laser-Ablated Zr Atoms with Water in Excess Argon
H2O
D2O
H218O
assignment
1604.6
1596.5
1577.6
1544.7
1539.4
1530.9
958.9
957.3
955.8
924.7
923.9
923.1
921.6
908.8
908.1
907.3
905.8
707.3
660.1
H2Zr(OH)2 sym-ZrH2
H2Zr(OH)2 asym-ZrH2
H2ZrO sym-ZrH2
HZrO Zr-H
H2ZrO asym-ZrH2
HZrOH Zr-H
90ZrO
1130.3
1110.1
1107.8
1098.2
958.9
957.3
955.8
922.4
921.6
920.8
919.3
907.4
1577.6
1544.7
1539.5
1530.5
912.8
911.2
909.7
881.2
880.4
879.5
877.9
865.7
865.0
864.2
862.7
92ZrO
94ZrO
H290ZrO Zr-O
H291ZrO
H292ZrO
H294ZrO
H90ZrO Zr-O
H91ZrO
906.0
904.4
680.7
635.4
H92ZrO
H94ZrO
H2Zr(OH)2 asym-Zr-(OH)2
H2Zr(OH)2 sym-Zr-(OH)2
Figure 4. Infrared spectra in the 1080-920 cm-1 region from co-
deposition of laser-ablated Ti with 0.4% (H2O + HDO + D2O) in
argon: (a) 1 h sample deposition, (b) 25 K annealing, (c) 20 min
broadband photolysis, and (d) annealing to 30 K.
Table 3. Infrared Absorptions (cm-1) from Co-deposition of
Laser-Ablated Hf Atoms with Water in Excess Argon
H2O
D2O
H218O
assignment
1675.8
1665.3
1626.5
1646.4
1615.6
958.7
921.0
902.9
690.7
660.4
1241.5
1233.0
1675.8
1665.3
1626.5
1646.4
1615.6
908.6
H2Hf(OH)2 sym-HfH2
H2Hf(OH)2 asym-HfH2
HHfO Hf-H
H2HfO sym-HfH2
H2HfO asym-HfH2
HfO
H2HfO Hf-O
HHfO Hf-O
H2Hf(OH)2 asym-Hf-(OH)2
H2Hf(OH)2 sym-Hf-(OH)2
H2TiO molecule is slightly lower in energy than the triplet
ground-state HTiOH molecule.
Similar B3LYP calculations were performed on H2M(OH)2
(M ) Ti, Zr, Hf) and HTi(OH)3 molecules, as shown in Figure
10. The H2M(OH)2 molecules were predicted to have 1A1 ground
state and C2V symmetry with the MH2 plane perpendicular to
the M(OH)2 plane.
1158.1
958.7
918.7
900.9
662.4
636.1
873.8
855.6
MO. The bands at 990.3, 987.8, and 985.5 cm-1 showed no
deuterium isotopic shift and are assigned to the TiO molecule
in different trapping sites in solid argon based on a recent matrix
isolation study of the Ti + O2 reaction.35 In a previous study
on thermal Ti atom and water reaction,6 a 1010 cm-1 band was
assigned to the TiO molecule; this band will be reassigned to
the H2TiO molecule, as will be discussed below. At the B3LYP/
6-311+G(d) level, the TiO molecule was predicted to have a
3
1
Table 4. Relative Energies (kcal/mol) for the F and D States of
Ti, Zr, and Hf
B3LYP
CCSD(t)
exptl
Ti
Zr
Hf
34.8
26.3
22.7
27.1
7.5
15.6
20.1
12.5
8.3
3∆ ground state with vibrational fundamental at 1043 cm-1
.
The 959.0 cm-1 band in the Zr + H2O experiment and the
958.7 cm-1 band in the Hf + H2O experiment are assigned to
the ZrO and HfO molecules on the basis of isotopic shifts and
previous works.35-37
Table 5. Calculated Bond Lengths (Å), Relative Energies (kcal/
mol), Vibrational Frequencies (cm-1), and Intensities (km/mol) for
3
1
the ∆ and Σ+ States of TiO, ZrO, and HfO
HMO. The 1483.1 and 968.7 cm-1 bands in the Ti + H2O
experiments went together through all experiments, suggesting
different modes of the same molecule. The upper band showed
a very small shift with H218O sample and was shifted to 1071.0
cm-1 when the D2O sample was used. The H/D isotopic ratio
of 1.3848 is characteristic of a Ti-H stretching vibration. The
lower band exhibited the characteristic titanium isotopic dis-
relative energy
bond
length
frequency
(intensity)
molecule
B3LYP
CCSD(t)
TiO (3∆)
TiO(1Σ+)
ZrO (1Σ+)
ZrO(3∆)
HfO(1Σ+)
HfO(3∆)
0
+28.8
0
0
+17.0
0
1.612
1.587
1.745
1.763
1.731
1.752
1043 (220)
1079 (273)
976 (164)
930 (172)
969 (120)
912 (132)
-8.5
+7.1
0
0
+23.3
+36.6
tribution for a single Ti atom;38 it shows a very small (0.9 cm-1
)
deuterium isotopic shift but was shifted to 928.1 cm-1 with the
H218O sample. The 16/18 ratio of 1.0437 indicates that this band
is mainly due to a Ti-O stretching vibration. These two bands
are assigned to the HTiO molecule. DFT calculations predicted
the HTiO molecule to have a 2A′′ ground state with Ti-H and
geometric parameters and relative stability are shown in Figure
9, and the vibrational frequencies and intensities are listed in
Table 7. At both B3LYP and CCSD(t) levels of theory, the
1
H2MO isomers were predicted to have A′ ground state with
nonplanar geometry and are more stable than the inserted
HMOH molecules. The inserted HTiOH and HZrOH molecules
Ti-O stretching vibrations at 1563 and 1034 cm-1
.
3
1
were calculated to have A′′ ground states, and HHfOH a A′
ground state. Our calculation results on H2TiO and HTiOH
molecules are in reasonable agreement with previous ab initio
molecular orbital calculations reported by Kudo and Gordon.34
Their calculations also predicted that the singlet ground-state
(35) Chertihin, G. V.; Andrews, L. J. Phys. Chem. 1995, 99, 6356.
(36) McIntyre, N. S.; Rhompson, K. R.; Weltner, W., Jr. J. Phys. Chem.
1971, 75, 3243.
(37) Simard, B.; Mitchell, S. A.; Humphries, M. R.; Hackett, P. A. J.
Mol. Spectrosc. 1988, 129, 186.
(38) CRC handbook; CRC Press: Boca Raton, FL, 1985. 46Ti, 8.0%;
47Ti, 7.5%; 48Ti, 73.7%; 49Ti, 5.5%; 50Ti, 5.3%; 90Zr, 51.4%; 91Zr, 11.2%;
92Zr, 17.1%; 94Zr, 17.5%; 96Zr, 2.8%.
(34) Kudo, T.; Gordon, M. S. J. Phys. Chem. A 1998, 102, 6967.

10684 J. Am. Chem. Soc., Vol. 122, No. 43, 2000
Zhou et al.
Figure 5. Infrared spectra in the 1585-1515, 1150-1090, and 970-900 cm-1 regions from co-deposition of laser-ablated Zr with 0.4% (H2O +
HDO + D2O) in argon: (a) 1 h sample deposition, (b) 25 K annealing, (c) 20 min broadband photolysis, and (d) annealing to 30 K.
Figure 7. Infrared spectra in the 980-840 cm-1 region from
co-deposition of laser-ablated Zr and Hf with 0.4% (H216O + H218O)
Figure 6. Infrared spectra in the 1020-920 cm-1 region from co-
in argon: (a) Zr, 1 h sample deposition, (b) Zr, 25 K annealing, (c) Zr,
deposition of laser-ablated Ti with 0.4% (H216O + H218O) in argon:
annealing to 30 K, (d) Hf, 1 h sample deposition, (e) Hf, 25 K annealing,
(a) 1 h sample deposition, (b) 25 K annealing, (c) 20 min broadband
and (f) Hf, annealing to 30 K.
photolysis, and (d) annealing to 30 K.
Absorptions at 1626.5 and 902.9 cm-1 in the Hf + H2O
In the Zr + H2O experiments, bands at 908.8, 908.1, 907.3,
and 905.8 cm-1 exhibited the intensity distribution for natural
abundance Zr isotopes.38 In the reactions of Zr with a H2O +
HDO + D2O mixture, these bands split into very closely spaced
doublets. In the reactions of Zr with a H216O + H218O mixture,
doublets were also observed, but with much greater separations.
The metal, deuterium, and oxygen isotopic shifts indicate the
presence of only one metal atom, one oxygen atom, and one
hydrogen atom. The 1544.7 cm-1 band exhibited the same
annealing and photolysis behavior as the 908.8 cm-1 band; the
deuterium isotopic shift indicates a Zr-H stretching vibration.
Accordingly, these bands are assigned to the Zr-H and Zr-O
stretching vibrations of the HZrO molecule. As with HTiO,
B3LYP calculations on the HZrO predicted a bent structure.
Frequency calculations on the ground 2A′ state produced
vibrational modes at 1634 and 937 cm-1, which require scaling
factors of 0.945 and 0.970 to fit the observed values.
experiments are assigned to the Hf-H and Hf-O stretching
vibrations of the HHfO molecule following the examples of
HTiO and HZrO. B3LYP calculations predicted the two
vibrational modes at 1683 and 933 cm-1 for the bent 2A′ ground-
state HHfO molecule.
H2MO. The 1010.5 cm-1 band was weak on sample deposi-
tion but was markedly increased on broadband photolysis. The
Ti isotopic splittings were clearly resolved, which indicate that
only one Ti atom is involved in this vibration. This band shifted
to 968.8 cm-1 for H218O sample and gave a 16O/18O isotopic
ratio of 1.0429. The Ti and oxygen-18 isotopic shifts suggest
that it is due to a terminal Ti-O stretching vibration. This band
has been assigned to the TiO molecule in previous thermal Ti
atom reactions with water in solid argon on the basis of the
metal and oxygen isotopic shifts and the absence of a deuterium
shift.6 However, in our experiments with 0.5 cm-1 resolution,
this band does show a very small deuterium shift (0.9 cm-1),

Reactions of Group IV Metal Atoms with Water Molecules
J. Am. Chem. Soc., Vol. 122, No. 43, 2000 10685
Figure 8. B3LYP-calculated geometric parameters (bond lengths in
angstroms; bond angles in degrees) and relative stability (kilocalories
per mole) of the HMO and MOH isomers.
Figure 9. B3LYP-calculated geometric parameters (bond lengths in
angstroms; bond angles in degrees) and relative stability (kilocalories
per mole) of the H2MO and HMOH isomers.
Table 6. Calculated Vibrational Frequencies (cm-1) and Intensities
(km/mol) for the Structures Described in Figure 8
molecule
frequency (intensity)
Table 7. Calculated Vibrational Frequencies (cm-1) and Intensities
HTiO (2A′′)
TiOH (4Σ-)
TiOH (2∆)
HZrO (2A′)
ZrOH (4Σ-)
ZrOH (2∆)
HHfO (2A′)
HfOH (4Σ-)
HfOH (2∆)
1563 (289), 1034 (260), 412 (180)
3990 (279), 743 (132), 169 (114)
3923 (258), 718 (68), 111 (95)
1634 (323), 937 (204), 534 (51)
3984 (283), 693 (100), 218 (232)
3958 (406), 738 (67), 298 (220)
1683 (170), 933 (156), 541 (39)
4001 (257), 685 (79), 194 (193)
3976 (310), 720 (54), 280 (122)
(km/mol) for the Structures Described in Figure 9
molecule
frequency (intensity)
H2TiO (1A′)
1730 (170), 1690 (465), 1082 (271), 636 (91),
536 (7), 427 (235)
HTiOH (3A′′)
HTiOH (1A′)
H2ZrO (1A′)
HZrOH (3A′′)
HZrOH (1A′)
H2HfO (1A′)
HHfOH (3A′′)
HHfOH (1A′)
3922 (158), 1591 (392), 721 (188), 464 (151),
448 (211), 304 (133)
3931 (306), 1674 (379), 779 (174), 401 (27),
346 (160), 269 (177)
1662 (180), 1620 (461), 942 (220), 590 (114),
528 (11), 457 (153)
3935 (209), 1577 (403), 679 (151), 414 (157),
407 (162), 323 (87)
3933 (298), 1680 (264), 717 (103), 404 (113),
379 (128), 276 (50)
1714 (138), 1683 (338), 932 (182), 663 (70),
549 (9), 498 (131)
3968 (219), 1601 (314), 683 (117), 420 (140),
409 (162), 265 (52)
3942 (230), 1679 (312), 708 (87), 523 (110),
512 (132), 317 (27)
and a broad band centered at 1010.0 cm-1 was observed in the
mixed H2O + HDO + D2O experiments. In concert, two bands
at 1646.8 and 1611.9 cm-1 tracked with the 1010.5 cm-1 band,
suggesting different modes of the same molecule. These two
bands exhibited very small shifts for the H218O sample. The
1611.9 cm-1 band was shifted to 1168.2 cm-1 for the D2O
sample and gave an isotopic H/D ratio of 1.3798; the deuterium
counterpart of the 1646.8 cm-1 band was overlapped by the
D2O absorptions. Accordingly, the 1010.5, 1611.9, and 1646.8
cm-1 bands are assigned to the Ti-O, antisymmetric, and
symmetric TiH2 stretching vibrations of the H2TiO molecule.
The H2TiO assignment receives further support from DFT
calculations. As has been mentioned, the H2TiO molecule was
of 1.3957 and 1.3896, respectively. In the mixed H2O + HDO +
D2O experiments (Figure 5), two additional bands at 1558.0
and 1119.2 cm-1 were observed; these two bands are due to
Zr-H and Zr-D stretching vibrations of the HDZrO molecule.
B3LYP calculations predicted a 1A′ ground-state H2ZrO
molecule with ZrH2 and Zr-O stretching vibrations at 1662,
1620, and 942 cm-1, which require scaling factors of 0.949,
0.950, and 0.982 to fit the observed frequencies. Of more
importance, the calculated isotopic shifts and splittings are
reproduced to substantial accuracy (-8.8, -0.5, and +0.2 cm-1
for D2ZrO, +0.4, +1.9, and -0.2 cm-1 for HDZrO), which
adds further support to the assignment.
1
predicted to have a A′ ground state and is slightly lower in
energy than the inserted HTiOH molecule. The Ti-O and TiH2
stretching vibrations were predicted to be 1082, 1690, and 1730
cm-1, which require scaling factors of 0.934, 0.953, and 0.952
to fit the observed values.
As with the titanium example, zirconium reacted with water
to give the H2ZrO. The formation of this species is confirmed
by absorptions at 1577.6 and 1539.4, and four bands at 924.7,
923.9, 923.1, and 921.6 cm-1. These bands can be grouped
together by noting their consistent behavior upon annealing and
photolysis. The relative intensities of the 924.7, 923.9, 923.1,
and 921.6 cm-1 bands matched those of natural isotopic
abundance zirconium and clearly indicate involvement of one
Zr atom. In the reactions of Zr with the H216O + H218O mixture,
these four bands split into four spaced doublets, while in the
mixed H2O + HDO + D2O experiment, a very closely spaced
triplet with and intermediate at 923.8 cm-1 was clearly observed
for the most intense 924.7 cm-1 band. The deuterium and
oxygen shifts and splittings indicate that two equivalent
hydrogen atoms and one oxygen atom are involved in this
molecule. The 1577.6 and 1539.4 cm-1 bands gave deuterium
counterparts at 1130.3 and 1107.8 cm-1 and defined H/D ratios
Similar bands at 1646.4, 1615.6, and 921.0 cm-1 in the
Hf + H2O experiments are assigned to the H2HfO molecule
following the examples of the H2TiO and H2ZrO molecules.
DFT calculations predicted that the H2HfO molecule also has a
1A′ ground state, with the three above modes at 1714, 1683,
and 932 cm-1
.
HMOH. In the previous thermal Ti atom and water reaction
study,6 two bands at 1538.9 and 699.7 cm-1 were been assigned
to the Ti-H and Ti-OH stretching vibrational modes of the
inserted HTiOH molecule. In the present experiments, a weak
band at 1549.1 cm-1 appeared on annealing and was destroyed
on photolysis when H2TiO absorptions were greatly enhanced.
This band is assigned to the Ti-H stretching vibration of the

10686 J. Am. Chem. Soc., Vol. 122, No. 43, 2000
Zhou et al.
Table 8. Calculated Vibrational Frequencies (cm-1) and Intensities (km/mol) of the Structures Described in Figure 10
sym-O-H
asym-O-H
sym-M-H
asym-M-H
sym-M-OH
asym-M-OH
H2Ti(OH)2
H2Zr(OH)2
H2Hf(OH)2
3952 (258)
3971 (217)
3995 (194)
3948 (339)
3968 (343)
3992 (351)
1773 (206)
1685 (257)
1729 (226)
1741 (411)
1649 (506)
1694 (431)
777 (154)
708 (161)
720 (159)
852 (342)
737 (355)
717 (303)
Table 9. Observed and Calculated Isotopic Frequency Ratios of
the HMO and H2MO Molecules
H/D
16O/18O
obsd
calcd
obsd
calcd
H2TiO
H2ZrO
H2HfO
sym-TiH
asym-TiH
Ti-O
sym-ZrH
asym-ZrH
Zr-O
1.4040
1.3905
1.0023
1.4067
1.4024
1.0022
1.0494
1.4081
1.0025
1.3969
1.0008
1.4050
1.0007
1.4087
1.0009
1.0009
1.0004
1.0430
1.0000
1.0000
1.0494
1.0000
1.0000
1.0540
1.0003
1.0439
1.0000
1.0498
1.0000
1.0553
1.0001
1.0000
1.0431
1.0000
1.0000
1.0499
1.0000
1.0000
1.0544
1.0001
1.0441
1.0000
1.0506
1.0000
1.0551
1.3798
1.0009
1.3957
1.3896
1.0025
sym-HfH
asym-HfH
Hf-O
1.3950
1.0025
1.3848
1.0009
1.3915
1.0015
HTiO
HZrO
HHfO
Ti-H
Ti-O
Zr-H
Zr-O
Figure 10. B3LYP-calculated geometric parameters (bond lengths in
angstroms; bond angles in degrees) of the H2M(OH)2 and HTi(OH)3
molecules.
Hf-H
Hf-O
1.0022
HTiOH molecule. The present DFT calculations predicted a 3A′′
ground-state HTiOH with bent geometry; the Ti-H and Ti-
OH stretching vibrational modes were calculated at 1591.2 and
721.0 cm-1 for 392:188 relative intensities. Our spectrum below
the 700 cm-1 region is noisy, and the Ti-OH mode was not
observed in our experiments.
wavelength pass filter and cannot be reproduced on further
annealing, which suggests an anion assignment. In general,
detaching electrons from negatively charged species requires
little energy, and easy photolysis by near-infrared or visible
radiation may suggest that the carrier is an anion. Cations are
usually easy to destroy by UV radiation.39 The upper band
shifted to 1071.0 cm-1 for the D2O sample, and the H/D isotopic
ratio of 1.3716 indicates that this band is a Ti-H stretching
A weak band at 1530.9 cm-1 in the Zr + H2O experiments
also appeared on annealing and was destroyed on photolysis.
The deuterium counterpart at 1098.2 cm-1 defines a 1.3940 H/D
ratio. This band is assigned to the Zr-H stretching mode of
the HZrOH molecule. Calculations predict this mode at 1577
vibration. The lower band exhibited a very small (2.3 cm-1
)
deuterium isotopic shift and a large oxygen isotopic shift (37.6
cm-1). These two bands are assigned to the Ti-H and Ti-O
stretching vibrations of the HTiO- anion. DFT calculations
3
cm-1 for the A′′ ground-state HZrOH molecule. The Zr-OH
stretching mode was calculated at 679 cm-1 with much lower
intensity and was not observed.
3
predicted the HTiO- anion to have a A′′ ground state with
bent geometry ( HTiO, 119.7°; Ti-H, 1.856 Å; Ti-O, 1.660
Å). The Ti-H and Ti-O stretching vibrations were predicted
There is no evidence for the HHfOH molecule. DFT
calculations indicate that the HHfOH molecule has a 1A′ ground
to appear at 1347 and 940 cm-1
.
state with a Hf-H stretching vibration at 1679 cm-1
.
In the Ti + H2O experiments, a 844.3 cm-1 band appeared
on annealing; this band was favored in higher water concentra-
tion experiments. This band was also observed in previous
thermal atom experiments and was tentatively assigned to
Ti(OH)x, with x ) 3 or 4.6 In the experiments reported in ref 6,
a quartet was clearly resolved in the mixed H2O + H218O
spectrum, indicating that three equivalent oxygen atoms are
involved. In the present study, a weak band in the Ti-H
stretching vibrational frequency region at 1634.3 cm-1 went
together with the 844.3 cm-1 band, suggesting different modes
of the same molecule. These two bands are assigned to the Ti-H
and Ti-OH stretching vibrations of the HTi(OH)3 molecule.
The HTi(OH)3 molecule was calculated to have a 1A1′′ ground
state with C3V symmetry (Figure 10), a strong doubly degenerate
Ti-OH stretching vibration at 816 cm-1, and a slightly weaker
H2M(OH)2. Four bands at 1688.3, 1666.2, 805.5, and 775.5
cm-1 grew in together on annealing, suggesting different modes
of the same molecule. These bands were also observed in
previous thermal atom reactions6 and were favored in high water
concentration experiments, suggesting that this molecule may
result from reaction of more than one water molecule. These
four bands are assigned to the TiH2 and Ti-(OH)2 stretching
vibrations of the H2Ti(OH)2 molecule. Absorptions at 1604.6,
1596.5, 707.3, and 660.1 cm-1 in the Zr + H2O experiments,
and at 1675.8, 1665.3, 690.7, and 660.4 cm-1 in the Hf + H2O
experiments, exhibited behavior very similar to that of the
H2Ti(OH)2 absorptions and are assigned to the analogous
H2Zr(OH)2 and H2Hf(OH)2 molecules.
The H2M(OH)2 assignments were further supported by DFT
calculations. As listed in Figure 10, all three H2M(OH)2
Ti-H stretching vibration at 1777 cm-1
.
1
molecules were predicted to have a A1 ground state and C2V
In all three systems, weak MO2 absorptions were observed
(TiO2, 917.0 cm-1; ZrO2, 818.0 cm-1; HfO2, 813.9 cm-1).35
These absorptions exhibited no shift when the isotopic H218O
sample was used, suggesting that the MO2 molecules might be
produced from a trace of O2 impurity in the system.
symmetry with the MH2 plane perpendicular to the M(OH)2
plane. As can be seen in Table 8, the calculated symmetric and
antisymmetric MH2 and M-(OH)2 stretching vibrations are in
good agreement with the observed values.
Other Absorptions. In the Ti + H2O experiments, two weak
bands at 1341.8 and 933.4 cm-1, present on sample deposition,
were destroyed on broadband photolysis with a 410 nm long-
(39) Bondybey, V. E.; Smith, A. M.; Agreiter, J. Chem. ReV. 1996, 96,
2113.

Reactions of Group IV Metal Atoms with Water Molecules
J. Am. Chem. Soc., Vol. 122, No. 43, 2000 10687
Table 9 compares the observed and calculated isotopic
vibrational frequency ratios of the major product HMO and
H2MO molecules. The observed ratios are in good agreement
with the calculated ratios, indicating that the present DFT
calculations predicted the normal modes correctly.
Reaction Mechanism. Co-condensation of laser-ablated Ti
and Zr atoms with water molecules in excess argon at 11 K
resulted in the formation of the insertion product HTiOH and
HZrOH molecules; however, there is no evidence of the HHfOH
molecule. Our theoretical calculations indicated that all three
insertion reactions (1)-(3) are exothermic (B3LYP values).
Ti(3F) + H2O(1A1) f HTiOH(3A′′) ∆E ) -63.5 kcal/mol (1)
Zr(3F) + H2O(1A1) f HZrOH(3A′′) ∆E ) -68.0 kcal/mol (2)
Hf(3F) + H2O(1A1) f HHfOH(1A′) ∆E ) -75.4 kcal/mol (3)
However, both HTiOH and HZrOH molecules have triplet
ground states, while HHfOH has a singlet ground state, so
reactions (1) and (2) conserve spin, while there is spin crossing
for reaction (3). As will be discussed, there is no spin crossing
from HHfOH(1A′) to H2HfO(1A′), and this suggests that HHfOH
is very short-lived, rapidly rearranging to form the H2HfO
molecule.
Figure 11. Potential energy surface for the Ti + H2O reaction at the
B3LYP level. Energies given are in kilocalories per mole and are
relative to the separated ground-state reactants: Ti(3F) + H2O(1A1).
The dashed lines indicate areas unexplored computationally.
The H2M(OH)2 and HTi(OH)3 absorptions increased on
annealing, suggesting that HMOH molecules can further react
with water via reactions (4)-(7). These reactions were calculated
to be exothermic (B3LYP values).
HTiOH + H2O f H2Ti(OH)2 ∆E ) -57.9 kcal/mol (4)
HZrOH + H2O f H2Zr(OH)2 ∆E ) -79.4 kcal/mol (5)
HHfOH + H2O f H2Hf(OH)2 ∆E ) -91.9 kcal/mol (6)
H2Ti(OH)2 + H2O f HTi(OH)3 + H2 ∆E ) -38.9 kcal/mol
(7)
The formation of MO and HMO species on sample deposition
indicates that part of the HMOH molecules formed in the gas
phase are dissociated to HMO, MO, and H2 or H during
deposition. Laser ablation of the metal target produces ground-
state atoms as well as excited atoms. The excited metal atom
reactions may give contributions to the formation of these
products. There is no evidence of the MH and MOH molecules.1
The HMO absorptions increased on annealing, suggesting that
HMO molecules can also be formed by reactions of MO and H
atoms.
Figure 12. Potential energy surface for the Zr + H2O reaction at the
CCSD(t) level. Energies given are in kilocalories per mole and are
relative to the separated ground-state reactants: Zr(3F) + H2O(1A1).
The dashed lines indicate areas unexplored computationally.
Figures 11-13 show qualitative singlet and triplet potential
energy surfaces for the Ti, Zr, and Hf + H2O reaction systems.
For the Ti and Hf systems, the relative stabilities of all species
calculated at the B3LYP and CCSD(t) levels are the same, so
the B3LYP calculation results were used for plots, but for the
Zr system, the B3LYP calculations predicted the relative stability
TiO(3∆) + H(2P) f HTiO(2A′′) ∆E ) -58.1 kcal/mol (8)
ZrO(1Σ+) + H(2P) f HZrO(2A′) ∆E ) -71.8 kcal/mol (9)
HfO(1Σ+) + H(2P) f HHfO(2A′) ∆E ) -52.3 kcal/mol (10)
3
1
of ∆ and Σ+ states of ZrO in error, so the CCSD(t) results
were used. In all three systems, there is no evidence of a metal
atom-water molecule adduct, and the present DFT calculations
failed to find true minima for such metal-water complexes.
Thus, the initial interaction is assumed to be direct metal atom
insertion into a HO-H bond to form the insertion HMOH
molecule. The 3F ground-state Hf is seen to exhibit spin-
forbidden crossing, leading to low-spin HHfOH; however,
neither Ti(3F) nor Zr(3F) exhibits spin crosssing.
The HTiOH absorptions were destroyed on broadband
photolysis, and two reaction paths were observed: rearrange-
ment to form the H2TiO isomer and H2 elimination to form the
TiO + H2. For the Zr and Hf + H2O systems, the H2ZrO and
H2HfO absorptions increased on annealing, and the ZrO and
HfO absorptions were not enhanced on broadband photolysis.
In previous thermal Ti atom experiments, H2TiO (which was
incorrectly assigned as TiO) was observed on sample deposition;
as the authors discussed, light from the hot furnace walls may
be capable of photolyzing the HTiOH molecules.6
From HMOH, two reaction paths are possible on the singlet
surface. One path is the hydrogen transfer from oxygen to the

10688 J. Am. Chem. Soc., Vol. 122, No. 43, 2000
Zhou et al.
Figure 14. B3LYP-calculated geometric parameters (bond lengths in
angstroms; bond angles in degrees) of the transition states.
Figure 13. Potential energy surface for the Hf + H2O reaction at the
B3LYP level. Energies given are in kilocalories per mole and are
relative to the separated ground-state reactants: Hf(3F) + H2O(1A1).
The dashed lines indicate areas unexplored computationally.
the ScO. As V atom has five valence electrons, chemical
bonding in H2VO can also be satisfied. Similar to Ti, both the
H2VO and VO formation paths are observed in the V + H2O
reaction.40 However, the H2MO+ (M ) Sc, Ti, V) intermediates
in the M+ + H2O reactions are quite different: there is no M-H
covalent bond, and these H2MO+ species can be viewed as ion-
molecule complexes.17,18
metal center to form H2MO through transition state 1 (TS1).
This process involves the breaking of the O-H bond and the
formation of a M-H σ bond and a M-O π bond. The other
path is the hydrogen transfer from oxygen to hydrogen through
transition state 2 (TS2). This transition state leads to H2
elimination to form the monoxides. This process involves the
breaking of the H-O bond and one covalent M-H bond, with
the formation of the H-H bond and a M-O π bond. On the
triplet surface, there is only the H2 elimination path through
transition state 3 (TS3), as no stable triplet H2MO was found.
The calculated structural parameters of the aforementioned
transition states are shown in Figure 14.
In the case of Ti, both the HTiOH and TiO have triplet ground
states. The transition state 3 from HTiOH(3A′′) to TiO(3∆) lies
lower in energy than the transition state 1 from HTiOH(1A′) to
H2TiO(1A′), and there is spin crossing leading to the H2TiO-
(1A′) product. In the case of Zr, the HZrOH also has a triplet
ground state with the singlet very closely in energy. There also
exists spin crossing from HZrOH(3A′′) to H2ZrO(1A′). Unlike
TiO, ZrO has a singlet ground state, formation of ZrO(1Σ+) from
HZrOH (3A′′) also requires spin crossing, and the transition state
3 lies higher in energy than the transition state 1, which makes
the formation of ZrO(1Σ+) unfavorable. In the case of Hf, both
HHfOH and HfO have singlet ground states, and the formations
of both H2HfO(1A′) and HfO(1Σ+) require no spin crossing. As
transition state 1 (leading the formation of H2HfO) lies lower
in energy than transition state 2 (leading the formation of HfO),
the formation of H2HfO dominates the reaction.
Conclusions
The reactions of Ti, Zr, and Hf atoms with water molecules
have been investigated using the laser ablation technique and
theoretical calculations. The metal atoms reacted with water
molecules to form the insertion products HMOH and H2M(OH)2
spontaneously on annealing in solid argon. Two photon-induced
reaction paths were observed for HTiOH: rearrangement to form
the H2TiO isomer and H2 elimination to form the monoxide
TiO. In the cases of Zr and Hf, the H2ZrO and H2HfO molecules
were produced on annealing spontaneously, but the H2 elimina-
tion to form the monoxide process was not observed on
photolysis. In addition, the HMO species were also observed
and identified.
The excellent agreement with frequencies and isotopic
frequency shifts from density functional calculations strongly
support the assignments of the aforementioned species. In
addition, qualitative analysis of the reaction paths leading to
the observed products are given, including several important
transition states.
Acknowledgment. We acknowledge helpful discussions
with Prof. Qike Zheng and Dr. Wenning Wang. This work is
supported by the Chinese NKBRSF.
The results on the Ti + H2O system are different from those
for the Sc + H2O system.20 As Sc has only three valence
electrons, there are not enough electrons to satisfy chemical
bonding in H2ScO, so the H2ScO species is unstable. The only
reaction path of HScOH is the H2 elimination process to form
JA0020658
(40) Zhang, L. N.; Dong, J.; Zhou, M. F.; Qin, Q. Z., manuscript in
preparation.