Photoabsorption and fluorescence cross sections of SiCl4 in the region of 6.2–31 eV

Abstract

Absolute photoabsorption and fluorescence cross sections of gaseous SiCl4 have been measured in the energy region 6.2–31 eV using synchrotron radiation as the light source. Higher order light from the 1-m Seya monochromator was suppressed by use of an Ar gas filter in the energy range 11.3–15.5 eV (110–80 nm) and a LiF window at hν<11.8 eV (105 nm). Emissions have been observed for the C̃ 2T2→à 2T2 and C̃ 2T2→X̃ 2T1 processes of the SiCl4+ molecular ion and the à 1B1→X̃ 1A1 and B13→X̃ 1A1 of the SiCl2 radical. The total fluorescence cross section has been determined to be 22.4±1.0 Mb at 21.22 eV. By comparing with the partial cross section for formation of the C̃ 2T2 ionic state [Carlson et al., J. Chem. Phys. 84, 641 (1986)], it has been concluded that the SiCl4+(C̃ 2T2) formed decays via radiative processes with quantum yield φ≈1. The experimental results provide information on the breakdown pathways of the SiCl4+(C̃ 2T2) ion state. The bands observed in photoabsorption and fluorescence excitation spectra have been assigned as the (4s, np, and np)←3t2, (4s and np)←1e, (4s and np)←1e, (4s and 4p)←2t2, and (np and nd)←2a1 Rydberg series. The ionization energies for the (2t2)−1 and (2a1)−1 processes have been found to be 15.04±0.03 and 18.17±0.03 eV, respectively.