L. Shao et al. / Chemical Physics Letters 343 &2001) 178±184
179
onto a 11 K CsI window, which was mounted on a
cold tip of a closed-cycle helium refrigerator 5Air
Products, Model CSW202) for 1 h at a rate of 2±4
mmol/h. Typically, 5±10 mJ/pulse laser power was
used. H2O and D2O were subjected to several
freeze±pump±thaw cycles before use. O2 5Shanghai
BOC, 99.6%) and 18O2 5Isotec Inc., >97%) were
used without further puri®cation. Infrared spectra
were recorded on a Bruker IFS113V spectrometer
at 0:5 cmÀ1 resolution using a DTGS detector.
Matrix samples were annealed at dierent tem-
peratures, and selected samples were subjected to
broadband photolysis using a high pressure mer-
cury lamp.
1010±900 and 770±400 cmÀ1 regions are shown in
Fig. 1, with the product absorptions listed in Table
1. Co-deposition of laser-ablated Ti atoms with
H2O=O2=Ar produced strong TiO2, O4À
5953:8 cmÀ1) [14,15] and very weak TiO absorp-
tions. New absorptions at 996.6, 753.6, 677.0,
483.2 and 414:9 cmÀ1 were observed on annealing
as with the TiO2 H2O=Ar experiments. Very
weak absorptions due to Ti H2O reaction were
also observed on broadband photolysis [16]. In the
spectra using a H216O 18O2 sample, the TiO2,
À
TiO and O4 absorptions were shifted as observed
before [13], and the 996.6, 753.6, 677.0, 483.2 and
414:9 cmÀ1 were shifted to 955.5, 745.1, 659.1,
480.9 and 414:3 cmÀ1
, respectively. When a
Quantum chemical calculations were performed
using the GAUSSIAN 98 program [7]. The three-
parameter hybrid functional according to Becke
with additional correlation corrections due to Lee,
Yang and Parr was utilized 5B3LYP) [8,9]. The
6-311++G5d,p) basis sets were used for Hand O
atoms, the all electron basis set of Wachters±Hay
as modi®ed by Gaussian was used for Ti atom
[10,11]. Reactants, various possible transition
states, intermediates and products were optimized.
The vibrational frequencies were calculated with
analytic second derivatives, and zero point vibra-
tional energies 5ZPVE) were derived. Transition
state optimizations were done with the synchro-
nous transit-guided quasi-Newton5STQN) method
[12], followed by the vibrational frequency calcu-
lations showing the obtained structures to be true
saddle points.
D2O 16O2 sample 5with about 40% HDO con-
tamination) was used, the 996:6 cmÀ1 band went
to 995:2 cmÀ1, and both the 753.6 and 677:0 cmÀ1
bands split into two bands at 747.8, 740:6 cmÀ1
and 671.0, 666:9 cmÀ1, as shown in Fig. 2.
The 996.6, 753.6, 677.0, 483.2 and 414:9 cmÀ1
bands are assigned to dierent modes of the
OTiꢀOH2 molecule. These bands were observed in
both TiO2 H2O=Ar and Ti H2O=O2=Ar ex-
periments, and increased together on annealing
and photolysis, suggesting dierent vibrational
modes of the same molecule. The 996:6 cmÀ1 band
showed very small deuterium isotopic shift 5about
1:4 cmÀ1). This band split into two bands at 955.5
3. Results and discussion
Laser ablation of a bulk TiO2 target in pure
argon produced TiO2 5946.8, 917:0 cmÀ1) and TiO
5990:2 cmÀ1) as the major products [13]. When
laser-ablated TiO2 was co-deposited with 0.25%
H2O in argon, new product absorptions at 996.6,
753.6, 677.0, 483.2 and 414:9 cmÀ1 were produced
on sample annealing. These absorptions also in-
creased on broadband photolysis and on subse-
quent 30 K annealing.
Fig. 1. Infrared spectra in the 1010±900 and 770±400 cmÀ1
regions from co-deposition of laser-ablated Ti atoms with 0.2%
H2O 0:5% O2 in argon. 5a) 1 h sample deposition at 11 K,
5b) after 28 K annealing, 5c) after 20 min broadband photolysis,
and 5d) after 30 K annealing.
Experiments were also done using metal Ti as
target and H2O O2 mixtures in excess argon as
reagent gas, and the representative spectra in the