Computational studies of SiH_{2}+SiH_{2} recombination reaction dynamics on a global potential surface fitted to ab initio and experimental data
Abstract
The recombination dynamics for the SiH_{2}+SiH_{2}→H_{2}Si=SiH_{2} reaction are studied by quasiclassical trajectory methods using a global potentialenergy surface fitted to the available experimental data and the results of various ab initio calculations. The potential surface is written as the sum of 18 manybody terms whose functional forms are motivated by chemical and physical considerations. The surface contains 41 parameters which are fitted to calculated geometries, fundamental vibrational frequencies, and energies for H_{2}Si=SiH_{2}, H_{2}Si=SiH, H_{2}Si=Si, HSi=Si, Si_{2}, H_{2}, and SiH_{2}, and to various calculated and/or measured reaction barrier heights and activation energies. In general, the equilibrium bond lengths and angles given by the global surface are in agreement with ab
initio results to within 0.03 Å and 0.5°, respectively. The calculated exothermicities for various reactions involving silicon and hydrogen atoms are in excellent agreement with previous MP4 calculations and with experimental data. The average absolute error is 1.90 kcal/mol. The average absolute deviation of the predicted fundamental vibrational frequencies for H_{2}Si=SiH_{2}, H_{2}Si=SiH, H_{2}Si=Si, and SiH_{2} from the results reported by Ho et al. is 52.9 cm^{}^{1}. The calculated barrier height for molecular hydrogen elimination from SiH_{2} is 34.27 kcal/mol with a backreaction barrier of 0.63 kcal/mol. The barrier for 1,2 elimination of H_{2} from H_{2}Si=SiH_{2} is 115.3 kcal/mol with a backreaction barrier of 30.7 kcal/mol. The formation cross sections for H_{2}Si=SiH_{2} decrease with both relative translational energy and internal SiH_{2} energy with translational energy being the more effective in reducing the cross sections. Thermally averaged formation cross sections vary from 66.3 Å^{2} at 300 K to 28.7 Å^{2} at 1500 K. The corresponding thermal rate coefficients lie in the range 24×10^{1}^{4} cm^{3}/mol s over this temperature range and exhibit a maximum at an intermediate temperature. The trajectory details indicate that the reaction exothermicity is primarily partitioned into the SiSi stretch and the HSiH bending modes upon formation of Si_{2}H_{4}. Energy transfer from the SiSi stretch to the SiH stretching modes is a relatively slow process occurring on a time scale of 10^{}^{1}^{2} s, which is about three to four times that previously computed for other polyatomic systems. Transfer from the SiSi stretch to the HSiH bending modes is a faster process.
 Publication:

Journal of Chemical Physics
 Pub Date:
 May 1988
 DOI:
 10.1063/1.454508
 Bibcode:
 1988JChPh..88.5948A
 Keywords:

 Computational Chemistry;
 Exothermic Reactions;
 Hydrogen Compounds;
 Recombination Reactions;
 Silicon Compounds;
 Chemical Reactions;
 Laser Induced Fluorescence;
 Potential Energy;
 Temperature Dependence;
 Atomic and Molecular Physics