Absorption spectra and aqueous photochemistry of [beta]-hydroxyalkyl nitrates of atmospheric interest

• Published in: Molecular physics Vol. 113; no. 15-16; p. 2179
• Main Authors: Romonosky, Dian E, Nguyen, Lucas Q, Shemesh, Dorit, Nguyen, Tran B, Epstein, Scott A, Martin, David B.C, Vanderwal, Christopher D, Gerber, R. Benny, Nizkorodov, Sergey A
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Ltd 01-08-2015
• Subjects: Nitrates; Photochemistry
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2015.1017020

Molar absorption coefficients were measured for select alkyl nitrates and [beta]-hydroxyalkyl nitrates in methanol. The presence of the [beta]-hydroxyl group has a relatively minor effect on the absorption spectrum in the vicinity of the weak n -> π* transition, which is responsible for photolysis of organic nitrates in the atmosphere. For both alkyl nitrates and [beta]-hydroxyalkyl nitrates, there is an enhancement in the absorption coefficients in solution compared to the gas-phase values. The effect of the [beta]-hydroxyl group on the spectra was modelled with molecular dynamics simulations using an OM2/GUGA-CI Hamiltonian for ethyl nitrate and [beta]-hydroxyethyl nitrate. The simulation provided a qualitatively correct shape of the low energy tail of the absorption spectrum, which is important for atmospheric photochemistry. The role of direct aqueous photolysis in removal of [beta]-hydroxyalkyl nitrates in cloud and fog water was modelled using a relative rate approach, and shown to be insignificant relative to gas-phase photochemical processes and aqueous OH oxidation under typical atmospheric conditions.