OBSERVATION OF AN ELECTRONIC STATE OF C2H NEAR 9 EV BY RESONANCE IONIZATION SPECTROSCOPY

A new electronic state of C2H, tentatively assigned as the 3p-sigma-2-PI Rydberg state, has been observed by resonance-enhanced multiphoton spectroscopy (REMPI). The observed absorptions originate from vibrationally excited C2H and C2D formed in the photodissociation of C2H2, C2D2, and C2HD at 193 nm in a molecular beam. Two-laser experiments and REMPI spectroscopy of photofragments of the dissociation of C2HD were used to assign the carriers of the observed spectra to C2H and C2D. Two-photon resonant, three-photon ionization (2 + 1 REMPI) of C2H and C2D is accompanied by substantial fragmentation to C2+ ions caused by multiple photon absorption by resonantly excited C2H and C2D. The identity of the lower C2H electronic state(s) (A approximately 2-PI or X approximately 2-SIGMA +) was not established.