VIBRONIC EXCITATION OF OXYGEN-ATOM TRANSFER FROM NO2 TO ETHYLENE BY LONG-WAVELENGTH VISIBLE-LIGHT IN A CRYOGENIC MATRIX

Chemical reaction has been observed upon irradiation of ethylene-NO2 pairs in solid Ar with continuous-wave dye laser light at visible wavelengths as long as 574 nm, well below the 398-nm dissociation limit of isolated NO2. Reaction products were acetaldehyde, ethylene oxide, NO, and ethyl nitrite radical, as established by FT infrared spectroscopy. Kinetic analysis of product absorbance growth showed that acetaldehyde is the prevalent final oxidation product of direct, single-photon photolysis of ethylene·NO2 pairs, while ethylene oxide is exclusively produced by yellow and shorter wavelength induced photodissociation of trapped ethyl nitrite radical. Experiments with trans- and cis-CHD=CHD yielded nitrite radical CHD-CHD-ONO under retention of stereochemistry but with scrambling in the epoxide product. On the basis of these results and those of our earlier work on NO2 photooxidation of cis- and trans-2-butene, a reaction path is proposed that involves O-atom transfer trom NO2 to the C=C bond to give a short-lived singlet oxirane biradical. The photolysis wavelength dependence of the reaction quantum efficiency indicates that NO2 reactant vibrational excitation plays an essential role and opens a reaction path that is unique to visible light induced alkene + NO2 chemistry in a matrix. © 1990 American Chemical Society.