Thermochemistry of HO2 + HO2 鈫?H2O4: Does HO2 Dimerization Affect Laboratory Studies?
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- 作者：Matthew K. Sprague ; Karl K. Irikura
- 刊名：Journal of Physical Chemistry A
- 出版年：2015
- 出版时间：July 9, 2015
- 年：2015
- 卷：119
- 期：27
- 页码：7052-7062
- 全文大小：366K
- ISSN：1520-5215
文摘
Self-reaction is an important sink for the hydroperoxy radical (HO2) in the atmosphere. It has been suggested (Denis, P. A.; Ornellas, F. R. J. Phys. Chem. A, 2009, 113 (2), 499鈥?06) that the minor product hydrogen tetroxide (HO4H) may act as a reservoir of HO2. Here, we compute the thermochemistry of HO2 self-reactions to determine if either HO4H or the cyclic hydrogen-bound dimer (HO2)2 can act as reservoirs. We computed electronic energies using coupled-cluster calculations in the complete basis set limit, CCSD(T)/CBS[45]//CCSD(T)/cc-pVTZ. Our model chemistry includes corrections for vibrational anharmonicity in the zero-point energy and vibrational partition functions, core鈥搗alence correlation, scalar relativistic effects, diagonal Born鈥揙ppenheimer, spin鈥搊rbit splitting, and higher-order corrections. We compute the Gibbs energy of dimerization to be (鈭?0.1 卤 1.6) kJ/mol at 298.15 K (2蟽 uncertainty), and (鈭?2.3 卤 1.5) kJ/mol at 220 K. For atmospherically relevant [HO2] = 108 molecules per cm3, our thermochemistry indicates that dimerization will be negligible, and thus H2O4 species are atmospherically unimportant. Under conditions used in laboratory experiments ([HO2] > 1012 molecules per cm3, 220 K), H2O4 formation may be significant. We compute two absorption spectra that could be used for laboratory detection of HO4H: the OH stretch overtone (near-IR) and electronic (UV) spectra.