Propylene, excited state reactions

Since rapid reaction is expected and found between oxygen and molecules excited to their triplet state (i.e., 0.01 mm. oxygen has a marked effect) a less pronounced effect, such as is observed with 2-pentanone, may naturally be ascribed to a reaction with excited singlet states. The evidence is not conclusive, but the addition of 560 mm. oxygen to 2-hexanone at room temperature using 3130 A. radiation resulted in only a slight decrease in the acetone and propylene yields, so that Brunet and Noyes2 concluded that an excited triplet state was not involved in the type II process. Recent evidence from other sources seems to support this point of view. (Editor s Note Added in Proof However, a recent article by Ausloos and Rebbert [J. Am. Chem. Soc., 86, 4512(1964)] indicated that the type II process occurs via a triplet excited state.)... 

Primary process (11) is also believed to proceed through a vibrationally excited ground-state molecule since it is also subject to pressure quenching, even at low pressures. This would fall in line with studies on the pyrolysis of l,S cyclohexadiene, which show that hydrogen, acetylene, ethylene, and benzene are products of the thermal reaction. Besides self-quenching, the use of inert gases such as xenon, carbon dioxide, propylene, and diethyl ether as quenchers has been investigated. ... 

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