Photodissociation Dynamics of C2H2, C2D2, and C2HD at 121.6 nm

Abstract

The product translational energy distribution P(Et) and the recoil anisotropy parameter β(Et) for acetylene (and isotopic variants) photodissociation at 121.6 nm have been obtained by detecting the H(D) atom fragment using the Doppler-selected time-of-flight (TOF) technique. A strong propensity toward the formation of the C2H(Ã 2Π) fragment was revealed. The resolution of this technique is sufficiently high to resolve the vibrational structures of a small polyatomic molecule. The vibrational spectroscopic constants of the C−H and C−C stretching modes for the C2H(Ã 2Π) state were obtained for the first time, and the mode-specific vibrational state distributions were deduced. It is conjectured that two distinct dissociation pathways, arising from the Rydberg−valence surface intersections, are involved in the title processes. The branching of these two pathways is governed by the initial absorption step.