Communication: State-to-state photodissociation study by the two-color VUV-VUV laser pump-probe time-slice velocity-map-imaging-photoion method

摘要

We demonstrate that combining two independently tunable vacuum ultraviolet (VUV) lasers and the time-slice velocity-map-imaging-photoion (VMI-PI) method allows the rovibronically state-selected photodissociation study of CO in the VUV region along with the state-selective detection of product C(~3P_(0,1,2)) using the VUV-UV (1+1′) resonance-enhanced photoionization and the VUV Rydberg autoionization methods. Both tunable VUV lasers are generated based on the two-photon resonance-enhanced four-wave mixing scheme using a pulsed rare gas jet as the nonlinear medium. The observed fine-structure distributions of product C(~3P_J), J = 0, 1, and 2, are found to depend on the CO rovibronic state populated by VUV photoexcitation. The branching ratios for C(~3P_0) + O(~3P_J): C(~3P_0) + O(~1D _2), C(~3P_1) + O(~3P_J): C(~3P_1) + O(~1D_2), and C(~3P_2) + O(~3P_J): C(~3P _2) + O(~1D_2), which were determined based on the time-slice VMI-PI measurements of C+ ions formed by J-state selective photoionization sampling of C(~3P_(0,1,2)), also reveal strong dependences on the spin-orbit state of C(~3P _(0,1,2)). By combining the measured branching ratios and fine-structure distributions of C(~3P_(0,1,2)), we have determined the correlated distributions of C(~3P_(0,1,2)) accompanying the formation of O(~1D_2) and O(~3P_J) produced in the VUV photodissociation of CO. The success of this demonstration experiment shows that the VUV photodissociation pump-VUV photoionization probe method is promising for state-to-state photodissociation studies of many small molecules, which are relevant to planetary atmospheres as well as fundamental understanding of photodissociation dynamics.