Direct Observation of the C + S₂ Channel in CS₂ Photodissociation

Carbon disulfide (CS₂) is a typical triatomic molecule. Its photodissociation process has generally been assumed to proceed to CS and S primary products via single bond fission. However, recent theoretical calculations suggested that an exit channel to produce C + S₂ should also be energetically accessible. Here, we report the direct experimental evidence for the C + S₂ channel in CS₂ photodissociation by using the velocity map ion imaging technique with two-photon UV and one-photon vacuum UV (VUV) excitations. The detection of the C (³P) products illustrates that the ground state and the electronically excited states of S₂ coproducts are formed within highly excited vibrational states. The very weak anisotropic distributions indicate relatively slow dissociation processes. The possible dissociation mechanism involves molecular isomerization of CS₂ to linear-CSS from the excited ¹B₂ (2¹Σ⁺) state via vibronic coupling with the ¹Π state followed by an avoided crossing with the ground state surface. Our results imply that the S₂ molecules observed in comets might be primarily formed in CS₂ photodissociation.