The ultraviolet and vacuum-ultraviolet photolyses of CH2O and CD2O in argon, CO, and CO-doped argon matrices have been performed between 8 and 10 K. The results of these experiments suggest that the photodecomposition mechanism of CH2O is a function of photon energy. The major products of photolysis are CO, H2, HCO, and H which presumably result from the two primary processes: CH20 + hv -* H + HCO (1) and CH20 + hv -* H2 + CO (2). No infrared detectable products were observed as a result of photolysis with a medium-pressure Hg lamp from exciting wavelengths above ~3000 Á. Photolysis into the continuum between 3000 Á and the air cutoff (~1 780 Á) with major lines at 2654 and 2537 Á resulted solely in the production of CO. Similar results were obtained from excitation into one of the Rydberg states with a hydrogen resonance lamp at 1215 A; thus it appears that reaction 2 is the major primary photodissociative process occurring in these wavelength regions. Based on relative intensities, more CO than HCO was obtained from photolysis at 1634 A; it appears that process 2 > 1 at this wavelength, although the possibility of secondary photolysis also exists (HCO -* + CO). A discussion of the photophysical processes occurring as a function of specific electronic absorptions is presented based on the results obtained from excitation into their continua by various resonance and filtered multiline light sources.

The vacuum-ultraviolet photolysis of propylene (C3Hg) in argon, nitrogen, CO, and CO-doped argon matrices has been performed between 8 and 10 K. The results of these experiments suggest that the photodecomposition of propylene occurs principally from the absorption of the 1215-Á hydrogen resonance line. Although this energy is above the ionization threshold (9.6 eV), no evidence of ionization was observed. The major products of photolysis are methylacetylene, aliene, methane, and acetylene, which presumably result from three primary processes: C3H6 + hv -*• CH4 + C2H2 (1); C3H6 + hv -H2 + CH2=C=CH2 (2); and C3Hg + hv -» H2 + CH3C=CH (3). Processes 1, 3, and possibly 2 are also the major reactions resulting from photolysis at 1745, 1634, 1580, and 1495 Á with various vacuum-ultraviolet resonance lamps. Based on relative intensities, process 1 > 3 > 2 as a result of photolysis with the 1215-Á line, but 1 > 2 3 for the other resonance line sources.

The ultraviolet and vacuum-ultraviolet photolyses of cyclobutanone (c-CsHeCO) in argon, carbon monoxide, and nitrogen matrices have been performed between 8 and 10 K. The results of these experiments suggest that the photodecomposition mechanism of cyclobutanone is a function of photon energy. The major products of photolysis observed are CO, c-CsHe, CH2CO, C2H4, and CsHg. These products result from at least two and possibly three primary photolysis processes: c-CsHeCO + hv -C2H4 + CH2CO (1); c-CsHeCO + hvc-CsH6 + CO (2), and possibly c-CsHgCO + hv -»• CsHe + CO (3). In process 2, propylene may also result from the isomerization of vibrationally excited cyclopropane, c-CsHe* * C3HÍ6 (2c), if it is not first quenched by the matrix, c-CsHg* + M -* c-CsHe + M (2b); where M is the matrix. No infrared detectable products were observed as a result of photolysis with a medium-pressure Hg lamp from exciting wavelengths above ~3100 Á. Photolysis into the predissociative region of the n ->• ir* (3350-2632 Á) band with the 3022-Á Hg line produced CO and c-CgHe only, while exposure to the full Hg arc with major lines at 3022, 2967, 2894, and 2804 Á resulted in infrared detectable products of CO, c-CsHe, CH2CO, and C3H6. Processes 1, 2, and possibly 3 are also the major reactions resulting from photolysis at 1745, 1634, 1580, and 1495 Á with various vacuum-ultraviolet resonance lamps, while no net photodecomposition or photoionization resulted at 1215 Á with a hydrogen resonance lamp. Based on relative intensities, the combination of processes 2 and 3 > 1 at all wavelengths employed in this study and (2c) and (3) are indistinguishable sources of CsHe. Although we obtained no direct evidence for the occurrence of (3) in this study nor have we been able to find any, we include its consideration because it is energically possible. Additional products obtained, due to secondary vacuum-ultraviolet photolysis below 1500 Á are methane, methylacetylene, aliene, and C20. The results from experiments using the CO matrix as a triplet quencher suggest that (2) may also proceed through ISC from the 1B2 state as observed for the first excited singlet, 1A2. A discussion of the photophysical and photochemical processes occurring as a function of specific electronic absorptions is presented. Some tentative vibrational assignments for the infrared frequencies of matrix-isolated cyclobutanone have also been made.

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