Disclosing rovibrational couplings and overlaps from irregularities in action spectra: Photodissociation of the 4v_CH rovibrational manifold of C₂H₂

The sim;243 nm photodissociation of rovibrationally excited acetylene molecules was exploited for detection of the 4ν_CH rovibrational manifold. The rovibrationally excited acetylene molecules were promoted to the FC region past the barrier on the ̃A¹A_u state and were subsequently dissociated adiabatically to C₂H(̃A²∏)+H and to a smaller extent nonadiabatically to C₂H̃X²Σ⁺+H. The efficient photodissociation of the prepared states led to enhanced H production and, in particular, resulted in larger photolysis cross sections for the rovibrational transitions of the (1214°0°) state than that of low J′ transitions of the (1030°0°) state.