PHOTOCHEMISTRY OF 2-BUTYNE IN SOLID XENON AT 10-K

The photochemistry of 2-butyne was studied by FTIR spectroscopy at 10 K in xenon matrices. The 2-butyne undergoes the following overall photochemical reactions: CH3-C≡C-CH3 → 2H-C≡C-H + H2; 2CH3-C≡C-CH3 → CH4 + CH3-C≡C-H + 2H-C≡C-H; and 2CH3-C≡C-CH3 → CH3-CH2-CH≡CH2 + 2H-C≡C-H. The reactions are observed in xenon, but not in argon, when 2-butyne is excited between 200 and 230 nm for M/R = 1/50, 1/100, 1/200, and 1/300. We postulate the lowest triplet excited state of 2-butyne becomes accessible in this region by spin-orbit coupling due to the external heavy-atom effect of xenon, resulting in triplet-state photochemistry. © 1990 American Chemical Society.