Theoretical studies of absorption cross sections for the C 1B2-X 1A1 system of sulfur dioxide and isotope effects

摘要

The C 1B2-X 1A1 photoexcitation of SO2 was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections σ~s of seven isotopologues (32S 16O2 , 33S 16O2 , 34S 16O2 , 36S 16O2 , 32S16O17O, 32S16O18O, 34S16O18O) were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces of the X andC states, which were calculated using the ab initio molecular orbital configuration interaction method. Numerous wave packet simulations were carried out under the adiabatic approximation and used to calculate the σ~s of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO2 can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated σ~s are in reasonable agreement with the recent experiment in the 190–228 nm region, and the isotope shifts of the peaks for 33S 16O2 and 34S 16O2 relative to the corresponding peaks for 32S 16O2 are in good agreement with the observed data. Relative to the of 32S 16O2, isotopic substitution shows a significant increment for those of 34S 16O2 and 36S 16O2 in the 190–228 nm region. This trend is consistent with the observed data.