Vibrationally mediated photodissociation of HCN

The dissociation mechanism of HCN by vibrationally mediated photodissociation has been examined. Exciting the C–H stretch with four quanta and photodissociating the molecule with 220 nm light generates CN in the first excited electronic A 2Π state rather than the ground X 2Σ+ state. The CN fragment is detected by probing the B 2Σ+←A 2Π(1–0) band and monitoring the laser-induced fluorescence (LIF) via the B 2Σ+→X 2Σ+(1–1) transition. The CN product distributions are found to be rotationally cold indicating that HCN dissociates from a linear geometry.