Computational studies of SiH2+SiH2 recombination reaction dynamics on a global potential surface fitted to ab initio and experimental data.

The recombination dynamics for the SiH2+SiH2→H2Si=SiH2 reaction are studied by quasiclassical trajectory methods using a global potential-energy 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 many-body 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 H2Si=SiH2, H2Si=SiH, H2Si=Si, HSi=Si, Si2, H2, and SiH2, 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 abinitio 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 H2Si=SiH2, H2Si=SiH, H2Si=Si, and SiH2 from the results reported by Ho et al. is 52.9 cm-1. The calculated barrier height for molecular hydrogen elimination from SiH2 is 34.27 kcal/mol with a backreaction barrier of 0.63 kcal/mol. The barrier for 1,2 elimination of H2 from H2Si=SiH2 is 115.3 kcal/mol with a backreaction barrier of 30.7 kcal/mol. The formation cross sections for H2Si=SiH2 decrease with both relative translational energy and internal SiH2 energy with translational energy being the more effective in reducing the cross sections. Thermally averaged formation cross sections vary from 66.3 Å2 at 300 K to 28.7 Å2 at 1500 K. The corresponding thermal rate coefficients lie in the range 2–4×1014 cm3/mol s over this temperature range and exhibit a maximum at an intermediate temperature. The... [ABSTRACT FROM AUTHOR]