Cold-surface photochemistry of primary and tertiary alkyl nitrites

Reflection-absorption infrared spectroscopy (RAIRS) is used to explore the photochemistry of primary and tertiary alkyl nitrites deposited on a gold surface. The primary alkyl nitrites examined for this study were n-butyl, isobutyl, and isopentyl nitrite. These compounds showed qualitatively similar spectra to those observed in previous condensed-phase measurements. The photolysis of the primary nitrites involved the initial formation of an alkoxy radical and NO, followed by production of nitroxyl (HNO) and an aldehydic species. In addition, the formation of nitrous oxide, identified from its distinctive transition near 2230 cm(-1), was observed to form from the self-reaction of nitroxyl. The reaction rates for cis and trans conformer decay, as tracked through their intense N═O stretching modes, were found to be significantly different, potentially due to a structural bias that favors HNO formation for the initial trans conformer photoproducts over recombination. Tert-butyl nitrite demonstrates only the trans conformer in the RAIRS spectra prior to photolysis; however, recombination of the initial NO and RO(•) photoproducts was observed to produce the cis conformer in the photolyzed samples. The primary photoproducts from tert-butyl nitrite can also react to form acetone and nitrosomethane, but the absence of HNO prohibits the formation of N(2)O that was observed for the primary alkyl nitrites. Additionally, the RAIRS spectrum of isobutyl nitrite co-deposited with water was measured to examine the photolysis of this species on a water-ice surface. No change in the identity of the photoproducts was observed in this experiment, and minimal frequency shifting (1-3 cm(-1)) of the vibrational modes occurred. In addition to being a known atmospheric source of NO and various aldehydes, our results point to cold surface processing of alkyl nitrites as a potential environmental source of nitrous oxide.