A study of the reactions of chlorine and fluorine atoms with SiH 2Cl 2 and SiHCl 3, with ultraviolet photoelectron spectroscopy

Abstract

The reactions Cl + SiHCl 3 and Cl + SiH 2Cl 2 have been investigated with UV photoelectron spectroscopy and bands associated with the primary reaction products SiCl 3 and SiHCl 2 have been observed. The first vertical ionization energies of SiCl 3 and SiHCl 2 have been measured as (9.24 ± 0.03) and (9.06 ± 0.02) eV respectively. The corresponding band onsets are (8.45 ± 0.05) and (8.40 ± 0.05) eV. Evidence is presented, based on the results of ab initio molecular orbital calculations at the 6–31G **/MP2 level, that the experimental band onsets are upper limits of the adiabatic ionization energies. For each radical, by comparing the computed vertical ionization energy with the measured value, the calculated adiabatic ionization energy has been corrected to yield an estimate of the experimental adiabatic ionization energy. Using this procedure, the adiabatic ionization energies of SiCl 3 and SiHCl 2 are evaluated as (8.05 ± 0.10) and (7.90 ± 0.10) eV respectively. HCl and SiCl 4 are found to be stable products of the Cl + SiHCl 3 reaction, and HCl, SiCl 2 and SiCl 4 are products of the Cl + SiH 2Cl 2 reaction sequence. Similar studies have been made for the F + SiH 2Cl 2 and F + SiHCl 3 reactions. F + SiH 2Cl 2 is notable in that it produces SiF 2, SiFCl, and SiCl 2 as secondary reaction products. The assignment of a reaction product band at (10.57 ± 0.01) eV vertical ionization energy to SiFCl has been supported by the results of ab initio molecular orbital calculations. For each reaction, spectra recorded at different reaction times allow a reaction scheme to be proposed.