15min:

NATHAN G. KUCHMAS AND C. A. BAUMANN, Department of Chemistry, The University of Scranton, Scranton, PA 18510-4626.

Visible irradiation (520 nm> >485 nm) of matrix-isolated biacetyl (C₄H₆O₂) results in the formation of a complex of cis -methylhydroxycarbene (CH₃COH) and ketene (CH₂CO), as well as other products. The wavelengths used in this study are longer than those necessary for the S₀-S₁ (X¹A_g -ùA_u) transition, indicating that the photolysis is the result of a multiphoton process. One such process is sequential, where the spin-forbidden S₀-T₁ (X¹A_g -ã³A_u) transition is followed by the allowed T₁-T₂ (ã³A_u -b³B_g) transition, with photoproducts emerging from the higher triplet (or following a radiationless transition to another state). A simultaneous two-photon process is also possible through the symmetry-forbidden S₀-S₂ (X¹A_g -B¹B_g) transition. Photoproduct formation as a function of irradiation flux and wavelength was used to sort out the relative contributions of each of these processes.