Direct ab initio dynamics study on the rate constants and kinetic isotope effect for the reactions of H atoms with GeD n (CH 3 ) 4− n ( n = 1–4)

Direct ab initio dynamic calculations are performed on the reactions of atomic hydrogen with GeD n (CH 3 ) 4− n ( n = 1–4) over the temperature range 200–2000 K at the PMP4SDTQ/6‐311 +G(3df,2p)//MP2/6‐31 +G(d) (for n = 2–4) and G2//MP2/6‐31 +G(d) (for n = 1) levels. The corresponding k H / k D ratios are then calculated in order to determine the kinetic isotope effect for the four reactions. For the simplest GeD 4 +H reaction, the only one that has available experimental data, the calculated canonical variational transition state theory incorporates small‐curvature tunneling correction (CVT/SCT) thermal rate constants, and the k H / k D values are in good agreement with the experimental values within the experimental temperature range 293–550 K. For the four GeD n (CH 3 ) 4−4 ( n = 1–4) reactions, the variational effect is small over the whole temperature range, whereas the small‐curvature effect is important in the lower temperature range. Finally, the overall rate constants are fitted to the three‐parameter expression over the whole temperature range 200–2000 K as 5.8 × 10 8 T 1.68 exp(−929/ T ), 1.7 × 10 8 T 1.80 exp(−691/T), 2.58 × 10 8 T 1.71 exp(−706/ T ), and 1.0 × 10 7 T 2.08 exp(−544/ T ) cm 3 mol −1 s −1 for the n = 4, 3, 2, and 1 reactions. Our work may represent the first theoretical study of the kinetic isotope effect for the H‐attack on the GeH bonding. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1366–1374, 2002