LONG-WAVELENGTH PHOTOCHEMISTRY OF MATRIX-ISOLATED BIACETYL

Author Institution: Department of Chemistry, The University of Scranton, Scranton, PA 18510-4626Visible irradiation (520 nm$>\lambda>$485 nm) of matrix-isolated biacetyl (C$_4$H$_6$O$_2$) results in the formation of a complex of \textit{cis}-methylhydroxycarbene (CH$_3$COH) and ketene (CH$_2$CO), as well as other products. The wavelengths used in this study are longer than those necessary for the S$_0$-S$_1$ (\~{X}$^1$A$_g$ -\~{A}$^1$A$_u$) transition, indicating that the photolysis is the result of a multiphoton process. One such process is sequential, where the spin-forbidden S$_0$-T$_1$ (\~{X}$^1$A$_g$ -\~{a}$^3$A$_u$) transition is followed by the allowed T$_1$-T$_2$ (\~{a}$^3$A$_u$ -\~{b}$^3$B$_g$) 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 S$_0$-S$_2$ (\~{X}$^1$A$_g$ -\~{B}$^1$B$_g$) transition. Photoproduct formation as a function of irradiation flux and wavelength was used to sort out the relative contributions of each of these processes