Two-photon photodissociation dynamics study of CS2: The S(1S) atom channel.

Two-photon photodissociation dynamics of carbon disulfide (CS2) were studied by means of the sliced velocity map ion imaging technique. The S(1S) + CS(X1Σ+) channel was directly observed from the measured images of S(1S) products in the wavelength range of 290.10-336.88 nm. The translational energy distributions and angular distributions of fragments have been derived. Rovibrational states of the CS(X1Σ+) co-products were partially resolved in the translational energy spectra and can be populated up to the energy limit of the available energy. Experimental results also show that the product anisotropy parameters are β2 > 0 and β4 ∼ 0. The latter indicates that the intermediate state reached by the first one photon excitation has a quite long lifetime, while the former suggests the molecules undergo a parallel transition from the intermediate state to the final state upon the second photon excitation and then experience a fast dissociation process. Combined with previous studies, we propose a possible dissociation mechanism: after absorbing two photons in the range of 290.10-336.88 nm, the CS2 molecule may undergo a sequential transition 1A1(1Σg+) ← 11B2(1Δu)/1A2(1Δu) ← X1Σg+, then directly dissociate or couple to other electronic states and dissociate.