Ab initio calculations of low-lying electronic states of vinyl chloride

摘要

The equilibrium geometries, vibrational frequencies, excitation energies, and oscillator strengths of vinyl chloride in the ground and five lowest-lying excited singlet states have been calculated using MP2, CIS, CASSCF, and MRCI methods with the 6-311 ++ G~** basis set. The geometries and vibrational frequencies of the ground and excited states are utilized to compute Franck-Condon factors. Calculated vibronic spectra for the transitions from the ground state to these five excited states are in agreement with experiment at 52 500-60 000 cm~(-1), with major contributions from the A(1 ~1A") <- X(1 ~1A') and C(2 ~1A') <- X(1 ~1A') transitions. In this study, two spin-forbidden transitions of b(1 ~3A") <- X(1 ~1A') and c(2 ~3A") <- X (1 ~1A') are calculated to locate in 45 000 - 54 000 cm~(-1), and could be responsible for the observed one-photon adsorption spectrum due to an intensity borrowing caused by the spin-orbit coupling of the Cl atom. Based on calculation, we speculate that upon the excitation of vinyl chloride at 193 nm the b (1 ~3A") or c(2 ~3A") excited state, instead of the (#pi#, #pi#~*), is initially prepared prior to the subsequent photodissociation processes.