Wavelength Dependent Photodissociation of OCS via F 3^1\Pi Rydberg State: CO(X^1\Sigma^+)+S(^1D_2) Product Channel

The vacuum ultraviolet photodissociation of OCS via the F 3^1\Pi Rydberg states was investigated in the range of 134-140 nm by means of the time-sliced velocity map ion imaging technique. The images of S(^1D_2) products from the CO(X^1\Sigma^+)+S(^1D_2) dissociation channel were acquired at five photolysis wavelengths, corresponding to a series of symmetric stretching vibrational excitations in OCS(F 3^1\Pi, v_1=0-4). The total translational energy distributions, vibrational populations and angular distributions of CO(X^1\Sigma^+, v) coproducts were derived. The analysis of experimental results suggests that the excited OCS molecules dissociate to CO(X^1\Sigma^+) and S(^1D_2) products via non-adiabatic couplings between the upper F 3^1\Pi states and the lower-lying states both in the C_\infty \textrmv and C_\rms symmetry. Furthermore, strong wavelength dependent behavior has been observed: the greatly distinct vibrational populations and angular distributions of CO(X^1\Sigma^+, v) products from the lower (v_1=0-2) and higher (v_1=3, 4) vibrational states of the excited OCS(F 3^1\Pi, v_1) demonstrate that very different mechanisms are involved in the dissociation processes. This study provides evidence for the possible contribution of vibronic coupling and the crucial role of vibronic coupling on the vacuum ultraviolet photodissociation dynamics.