4
5
6
D. Gerlich and S. Horning, Chem. Rev., 1992, 92, 1509.
mine the appearance potentials (APÏs) of C H ` and C D `.
2
2
2 2
D. Smith and P. Spanel, Mass Spectrom. Rev., 1996, 14, 255.
V. G. Anicich, J. Phys. Chem. Ref. Data, 1993, 22; Y. Ikezoe, S.
Matsuoka, M. Takebe and A. A. Viaggiano, Gas Phase IonÈ
Molecule Reaction Rate Constants through 1986, Maruzen,
Tokyo, 1987, p. 1469.
Here we arrive at AP \ 13.135 eV at 0 K for the C H ` for-
2
2
mation in line with our previous work.20 This number is 10
meV lower than the thermochemical limit recommended by
Lias et al.26 For the C D ` formation we arrive at
2
2
AP \ 13.233 eV at 0 K. Combining the AP of C H ` from
7
D. Smith, N. G. Adams and E. E. Ferguson, Int. J. Mass
2
2
Spectrom. Ion Proc., 1984, 61, 15.
Lias et al. with the shift of 69 meV discussed in the previous
paragraph leads to an expected AP of the C D ` of 13.214 eV
which is about 20 meV below the value derived in this work.
Again, one should note that the AP determined in our experi-
ment could be higher than the thermochemical limit due to a
small barrier.
8
9
M. Hawley and M. A. Smith, J. Chem. Phys., 1992, 96, 1121.
K. Yamashita and E. Herbst, J. Chem. Phys., 1992, 96, 5801.
2
2
10 E. Herbst and K. Yamashita, J. Chem. Soc., Faraday T rans.,
1993, 89, 2175.
11 D. Smith, J. Glosik, V. Skalsky, P. Spanel and W. Lindinger, Int.
J. Mass Spectrom. Ion Proc., 1993, 129, 145.
12 S. A. Maluendes, A. D. McLean and E. Herbst, Chem. Phys. L ett.,
1994, 217, 571.
The k(E) curves measured directly in this work for the Ðrst
time are in agreement with MIKES experiments14h16 showing
a metastable ion signal as well as with QET calculations.15,16
SigniÐcantly larger k(E) values were calculated by Lorquet et
al.19 However these calculations were based on a planar struc-
ture of the ethene ion, while ab initio QCISD calculations12
show that the ethene ion has a non planar equilibrium
geometry. Unfortunately the normal frequencies of C H `
13 R. Stockbauer and M. G. Inghram, J. Chem. Phys., 1975, 62,
4862.
14 D. H. Williams and G. Hvistendahl, J. Am. Chem. Soc., 1974, 96,
6755.
15 I. Nenner, H. Nguyen Nghi and R. Botter, Adv. Mass Spectrom.,
1975, 6, 885.
16 N. Vial, I. Nenner and R. Botter, J. Chim. Phys. Phys.ÈChim.
Biol., 1979, 76, 1091.
2
4
have not been listed in ref. 12. In the future new k(E, J) calcu-
lations of the unimolecular decay of ethene ions based on
these ab initio frequencies may contribute to a better under-
standing of the reaction mechanism.
17 R. G. Cooks, J. H. Beynon, R. M. Caprioli and G. R. Lester,
Metastable Ions, Elsevier, Amsterdam, 1973.
18 C. Sannen, G. Raseev, C. Galloy, G. Fauville and J. C. Lorquet,
J. Chem. Phys., 1981, 74, 2402.
19 M. Desouter-Lecomte, C. Sannen and J. C. Lorquet, J. Chem.
Phys., 1983, 79, 894.
4
Summary
20 J. Mahnert, F. Guthe and K.-M. Weitzel, Ber. Bunsen Ges. Phys.
Chem., 1996, 100, 1899.
The H /D loss reaction from h -ethene and d -ethene has
21 F. Guthe, M. Malow, K.-M. Weitzel and H. Baumgartel, Int. J.
Mass Spectrom. Ion Proc., 1998, 172, 47.
2
2
4
4
been investigated by the TPEPICO technique in a reÑecting
ion time of Ñight spectrometer. The RETOF spectra presented
in this work show that the title reactions take place on the ls
timescale, i.e. are metastable reactions. By direct simulation of
the breakdown curves complete k(E) curves for the two reac-
22 T. Baer, J. A. Booze and K.-M. Weitzel, in V acuum Ultraviolet
Photoionization and Photodissociation of Molecules and Clusters,
ed. C. Y. Ng, World ScientiÐc, Singapore, 1991.
23 K.-M. Weitzel, J. Mahnert and M. Penno, Chem. Phys. L ett.,
1994, 224, 371.
tions have been derived. The threshold values are k(E ) \ 7.0
24 K.-M. Weitzel, T rends Chem. Phys., 1997, 6, 143.
25 F. Guthe and K.-M. Weitzel, Ber. Bunsen Ges. Phys. Chem., 1997,
101, 484.
26 S. G. Lias, J. E. Bartmess, J. F. Liebmann, J. L. Holmes, R. D.
Levin and W. G. Mallard, J. Phys. Chem. Ref. Data, 1988, 17,
Suppl. 1.
0
] 105 s~1 for the h -ethene and k(E ) \ 2.5 ] 104 s~1 for the
4
0
d -ethene. The dissociation energy of the C H ` ion is E \
4
2
4
0
2.628 eV, that of the C D ` ion is E \ 2.714 eV. The k(E)
2
4
0
curve of d -ethene is shifted by 86 meV to higher excitation
4
energy with respect to that of h -ethene. The major part of
27 U. Boesl, R. Weinkauf and E. W. Schlag, Int. J. Mass Spectrom.
4
that shift can be explained by the di†erence in *ZPVE for the
Ion Proc., 1992, 112, 121.
two reactions. For the future more detailed k(E, J) calcu-
lations based on high level ab initio molecular parameters
seem rewarding.
28 K.-M. Weitzel, Habilitationsschrift, 1997, Freie Universitat
Berlin, Shaker Verlag, Aachen, 1998.
29 K.-M. Weitzel, J. A. Booze and T. Baer, Int. J. Mass Spectrom.
Ion Proc., 1991, 107, 301.
30 K.-M. Weitzel, J. A. Booze and T. Baer, Chem. Phys., 1991, 150,
263.
31 T. Beyer and D. F. Swinehart, Commun. Assoc. Comput.
Acknowledgement
Financial support by the Deutsche Forschungsgemeinschaft
(We 1330/6) is gratefully acknowledged.
Machines, 1973, 16, 379.
32 T. Shimanouchi, T ables of Molecular V ibrational Frequencies,
Nat. Stand. Ref. Data Ser., NBS No. 39, 1972, 1.
33 R. A. Marcus, J. Chem. Phys., 1952, 20, 359.
34 H. M. Rosenstock, K. Draxl, B. W. Steiner and J. T. Herron, J.
Chem. Ref. Data, 1977, 6, Suppl. 1.
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