Velocity map imaging studies of the photodissociation of CS2 by two-photon excitation at around 303–315 nm

Two-photon dissociation dynamics of carbon disulfide (CS2) have been studied by using the time-sliced velocity map ion imaging technique. Images of the S (1D2) and S (3P0) photoproducts formed in the CS2 photodissociation are acquired at four photolysis wavelengths from 303 nm to 315 nm. Vibrational states of the CS co-products are partially resolved and identified in the images. The CS (X1Σ+) products are highly vibrationally excited with moderate rotational excitation. The spin–orbit state-specific dissociation dynamics are also investigated by measuring the images of three S (3PJ) spin–orbit states (J=0, 1, and 2) at photolysis wavelength 303.878 nm. The branching ratios of CS (a3Φ)/CS (X1Σg+) are determined to be 0.05 ± 0.02, 0.17 ± 0.04, and 0.26 ± 0.05 for the three spin–orbit states S (3P0), S (3P1), and S (3P2) respectively, implying a strong spin–orbit coupling exists in the dissociation process. The averaged anisotropy parameters β2>0 and β4∼0 suggest that the CS2 molecules undergo a sequential transition 21B2(21Σ+)←11B2(1Δu)←X1Σg+ with the intermediate state 11B2 having a long lifetime, followed by nonadiabatic and spin–orbit couplings to other electronic states and then dissociate.