Photodissociation tudy of CS_2 at 193 nm using slice imaging

摘要

The photodissociation of CS_2 at 193 nm (51700) cm~(-1)) is studied using the slice imaging technique, and velocity distributions for state selected S(~3P_(2,1,0) and S(~1D_2) photofragments are measured. From the analysis of the speed distributions we determine the S(~3P_(2,1,0)/S(~1D_2) branching ratio to be 1.5+-0.4. The partially resolved S-atom speed distributions peak at intermediate speeds, indication substantial rovibrational excitation of the CS sibling fragment. By modeling this CS propensity using a Franck-Condon analysis between the X(~1#SIGMA#_g~+) and the excited ~1B_2 state, we estimate the origin of the excited state to be located at approx45600 cm~(-1). From the S-atom angular distributions, we determine the spatial anisotropy parameter #beta#, and find that the value for S(~3P_(2,1,0) is slightly8 speed dependent with an average value of approx0.2. The #beta# values for S(~1D_2) are strongly speed dependent, reaching the value of 0.6 at intermediate speeds and an average value of 0.2 at low and high speeds, From the observed #beta# values we conclude that the CS_2 molecule is highly bent (approx115deg) prior to dissociation, while the dissociation lifetime is on the order of a rotational period.