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Visible irradiation (520 nm$>\lambda>$485nm)ofmatrix-isolatedbiacetyl(C$_4$H$_6$O$_2$)resultsintheformationofacomplexofcis-methylhydroxycarbene(CH$_3$COH)andketene(CH$_2$CO),aswellasotherproducts.ThewavelengthsusedinthisstudyarelongerthanthosenecessaryfortheS$_0$-S$_1$ (~{X}$1$A -~{A}$1$A) 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 -~{a}$3$A) transition is followed by the allowed T$1$-T$2$ (~{a}$3$A -~{b}$3$B) 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 -~{B}$1$B) transition. Photoproduct formation as a function of irradiation flux and wavelength was used to sort out the relative contributions of each of these processes.