Direct identification of photofragment structures formed in the 193 nm photodissociation of thiophene

Article abstract of DOI:10.1021/j100006a019

An experimental scheme which involves vacuum ultraviolet photoionization mass spectrometric sampling of laser photodissociation products in a pulsed supersonic molecular beam has been used to identify the isomeric structures of the 193 nm photofragments from thiophene. The primary products observed are vinylacetylene (H₂C=CH-C≡CH), acetylene (C₂H₂), and thioketene (H₂C=C=S). Using the 2 + 1 resonance-enhanced multiphoton (REMPI) scheme, we find that S atoms are produced predominantly (≥96%) in ³P_J states with a fine structure distribution of ³P₂:³P₁:³P₀ = 0.82 ± 0.03:0.15 ± 0.03:0.03 ± 0.03. These experimental results indicate that the major dissociation channels are CH₂=CH-C≡CH + S(³P) and CH=CH + CH₂=C=S. Ab initio multiconfiguration self-consistent-field calculations have been made to rationalize these experimental observations.