Quantum Yields for Photochemical Production of NO2 from Organic Nitrates at Tropospherically Relevant Wavelengths

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• 作者：Christina M. Higgins ; Louise A. Evans ; Guy C. Lloyd-Jones ; Dudley E. Shallcross ; David P. Tew ; Andrew J. Orr-Ewing
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：April 17, 2014
• 年：2014
• 卷：118
• 期：15
• 页码：2756-2764
• 全文大小：372K
• 年卷期：v.118,no.15(April 17, 2014)
• ISSN：1520-5215

文摘

Absorption cross-sections and quantum yields for NO₂ production (桅_NO2) are reported for gaseous methyl, ethyl, n-propyl, and isopropyl nitrate at 294 K. Absorption cross-sections in the wavelength range of 240鈥?20 nm agree well with prior determinations. NO₂ quantum yields at photoexcitation wavelengths of 290, 295, and 315 nm are unity within experimental uncertainties for all of the alkyl nitrates studied and are independent of bath gas (N₂) pressure for total sample pressures in the range of 250鈥?00 Torr. When averaged over all wavelengths and sample pressures, values of 桅_NO2 are 1.03 卤 0.05 (methyl nitrate), 0.98 卤 0.09 (ethyl nitrate), 1.01 卤 0.04 (n-propyl nitrate), and 1.00 卤 0.05 (isopropyl nitrate), with uncertainties corresponding to 1 standard deviation. Absorption cross-sections for ethyl nitrate, isopropyl nitrate, and two unsaturated dinitrate compounds, but-3-ene-1,2-diyl dinitrate and (Z)-but-2-ene-1,4-diyl dinitrate in acetonitrile solution, are compared to gas-phase values, and over the wavelength range of 260鈥?15 nm, the gas-phase values are well-reproduced by dividing the liquid-phase cross-sections by 2.0, 1.6, 1.7, and 2.2, respectively. Reasonable estimates of the gas-phase absorption cross-sections for low-volatility organic nitrates can therefore be obtained by halving the values for acetonitrile solutions. The quantum yield for NO₂ formation from photoexcitation of but-3-ene-1,2-diyl dinitrate at 290 nm is significantly lower than those for the alkyl (mono) nitrates: a best estimate of 桅_NO2 鈮?0.25 is obtained from the experimental measurements.