Photolysis of 2-pentyl nitrite : quantum yield and relevance to atmospheric chemistry
One of the remaining problems associated with the photo-degradation of organic species in the atmosphere, is concerned with the mechanisms of C5 and larger fragments. In this respect the 2-pentoxy radical has been chosen as a model radical. The subsequent mechanisms for it are thought to be similar to those for all other larger species. The photolysis of 2-pentyl nitrite in the near ultraviolet (UV) region at 328-383 nm resulted in the formation of 2-pentoxy radicals and nitric oxide with the quantum yield of 0.97 ± 0.08 at 298-393K, consistent with the assumption that the quantum yield was unity for alkyl nitrites. In the present work, tert-butyl nitrite has been shown to be unity. The reactions of the model radical were investigated in inert (CF4), and oxygen atmospheres, by end product analysis using on-line gas-liquid chromatography. The expected reaction routes were: decomposition, oxidation (β-H atom abstraction), and 1,5-H shift isomerisation which would produce acetaldehyde, 2-pentanone and acetone respectively. Its reaction scheme was evaluated by comparing the experimental with model results, derived by the Gear Algorithm. The estimated or calculated rate constants in the literature were "brute force" adjusted to adapt the modelling results to the experimental results. Our investigations suggested, among the rate constants for the 2-pentoxy radical: kdec 9.2 x 103s-1: CH3CH(O)(CH2)2CH3 → n-CH3CHO + n-C3H7, k02 7.0 x 105M-1s-1: CH3CH(O)(CH2)2CH3+02 → CH3C(O)(CH2)2CH3 + HO2, and kisom 1.4 x 104s-1; CH3CH(O)(CH2)2CH3 → CH3CH(OH)(CH2)2CH2) The 1,5-H shift isomerisation is relatively fast. The Arrhenius parameters of these rate constants were also modified.