Branching Ratio Measurements for Vacuum Ultraviolet Photodissociation of ¹²C¹⁶O

Abstract

The branching ratios for the spin-forbidden photodissociation channels of (12)C(16)O in the vacuum ultraviolet (VUV) photon energy region from 102,500 (12.709 eV) to 106,300 cm(-1) (13.180 eV) have been investigated using the VUV laser time-slice velocity-map imaging photoion technique. The excitations to three (1)Σ(+) and six (1)Π Rydberg-type states, including the progression of W(3sσ) (1)Π(v' = 0, 1, and 2) vibrational levels of CO, have been identified and investigated. The branching ratios for the product channels C((3)P) + O((3)P), C((1)D) + O((3)P), and C((3)P) + O((1)D) of these predissociative states are found to depend on the electronic, vibrational, and rotational states of CO being excited. Rotation and e/f-symmetry dependences of the branching ratios into the spin-forbidden channels have been confirmed for several of the (1)Π states, which can be explained using the heterogeneous interaction with the repulsive D'(1)Σ(+) state. The percentage of the photodissociation into the spin-forbidden channels is found to increase with increasing the rotational quantum number for the K(4pσ) (1)Σ(+) (v' = 0) state. This has been rationalized using a (1)Σ(+) to (1)Π to (3)Π coupling scheme, where the final (3)Π state is a repulsive valence state correlating to the spin-forbidden channel.