Carbon dioxide in the pressure range of 50–600 Torr has been photolyzed at 1470 Å. An initial quantum yield of Φ(CO) = 1.0 was observed. The O2/CO ratio was 0.35 ± 0.02. While the O2/CO ratio remained constant, the rate of CO formation decreased significantly with an increase in the photolysis time. Such a lowering of the conversion rate is attributed to a light attenuation due to solid deposit being formed on the lamp window.

Liquid cyclohexane and cyclohexane solutions were photolyzed at 1236 and 1470 Å. The products and quantum yields for cyclohexane photolysis at 1470 Å are hydrogen (1.0), cyclohexene (0.94), dicyclohexyl (0.06), ethylene (0.003) and butadiene (0.001). Products and relative yields at 1236 Å are hydrogen (1.0), cyclohexene (0.93), dicyclohexyl (0.05), ethylene (0.06) and butadiene (0.02). The addition of benzene or cyclohexene as solutes caused drastic reductions in the rate of cyclohexane decomposition. A significant fraction of the decreases in the product yields is attributed to the scavenging of hydrogen atoms by the solute. The ratio of the rate constant for hydrogen atom addition to benzene to that of hydrogen abstraction from cyclohexane is about 300. Neutral excited cyclohexane molecules are found to be important intermediates, and the major effects of benzene and cyclohexene as solutes are accounted for by quenching of these excited species. The rate-constant ratio for energy transfer to the solute and dissociation of the excited intermediate is about 3.2 liter/mole.

The photochemistry of azoisopropane is reinvestigated at 366 nm over an extended pressure range by using n-butane as an added bath gas, and over a range of temperature from 217" to 180°C. The Stern-Volmer type plot of the NS product quantum yield is interpreted in terms of the decomposition of the vibrationally excited upper singlet and triplet states, with the onset of the dissociation of the vibrationally equilibrated triplet state as the temperature is increased. The energy barrier for the dissociation of the vibrationally equilibrated first triplet state is found to be 8.8 kcal/mole. Triplet sensitization experiments with biacetyl correlate with our observations, and it is suggested that the proposed mechanism is generally applicable to the photodissociation of acyclic azoalkanes at 366 nm, based on a comparison of our data with those of Wu and Rice on hexafluoroazomethane. 99

Abstract'The T * t n excited state kinetics of hexafluoroacetone are reinvestigated in the presence of a vibrational relaxer and sufficient triplet state quencher so that only the reactions of the electronically excited upper singlet state are examined. From a Stern-Volmer type analysis it is concluded that vibrational relaxation of the initially formed vibrationally and e)ectronically excited upper singlet state is via a multistage collisional mechanism. An activation energy of about 6 kcal/mole is reported for the unimolecular decomposition of the upper singlet state.

Nitrous oxide, in the pressure range of 1–760 torr, has been photolyzed at 1470 Å. The rates of N2, O2, and NO formations are independent of the N2O pressure. The quantum yields are φN2=1.40±0.02, φO2=0.58±0.03, and φNO=0.78±0.03. A reaction scheme for the photodecomposition of nitrous oxide is given, and a quantitative correlation of the observed product yields with those expected from the proposed mechanism is demonstrated.