SPECTROSCOPY AND PHOTODISSOCIATION DYNAMICS OF THE PREDISSOCIATING $^{1}B_{2}$ STATE OF THE $CS_{2}$

Abstract

Author Institution: Department of Chemistry, University of Waterloo; Department of Chemistry, Laboratoire de Chimie Th\'{e}oriquePhotofragment spectroscopy has been used to study the spectroscopy and detailed photodissociation dynamics of the predissociating $^{1}B_{2}$ state of $CS_{2}$. The target is prepared in a seeded supersonic expansion, yielding a rotationally cold sample with variable vibrational temperature. Photolysis by a pulsed dye laser in the 215-200 nm wavelength range gives rise to two possible channels: CS_{2}+h\nu\rightarrow CS_{2}^*(^{1} B_{2})\rightarrow CS (X^{1}\Sigma^*)+S(^{1} D_{2})\rightarrow CS (X^{1}\Sigma^{+})+ S(^{3} P_{1}) with a quantum yield for photodissociation of -100\%. These channels can be probed separately by excitation of sulfur resonance lines at 144.8 nm for the $^{1}D_{2}$ channel, and between 147.4nm and 148.7nm for the three spin-orbit sublevels of the $^{3}P_{1}$ channel, using frequency upconverted pulsed dye laser radiation. By fixing the detection wavelength to a specific product channel, we can measure an excitation spectrum for that channel. Thus, We were able to msp out the absorption spectrum of jet-cooled $CS_{2}$, and we are using a semi-rigid bender treatment to analyse the very complicated spectrum. After identifying the different bands, we probed the dynamics of the photodissociation process by fixing the photolysis wavelength and scanning the VUV probe laser radiation. We observed a strong product channel selectivity resulting from exciting different vibrational levels in the $^{1}B_{2}$ state. The S($^{3}P_{2}$) product is strongly favoured over all other possible products for $K=0$ levels, whereas a more democratic product distribution is observed for $K=1$ levels. Although this selectivity is general for the $^{1}B_{2}$ state, it gets stronger for lower vibrational levels