Peroxy radical can complex with water vapor. These complexes affect the chemistry of the troposphere. In this study, (β-HEP; hydroxyethyl peroxy radical) serves as a model system for investigating the effect of water vapor on the kinetics and product branching ratio of the self reaction of peroxy radicals. The effect of water vapor on the self-reaction rate coefficient was investigated in the range 274–296 K with water vapor between 1.0 x 1015 and 2.5 x 1017 molecules cm-3 at 200 Torr total pressure by slow-flow laser flash photolysis coupled with UV time-resolved spectroscopy and long-path, wavelength modulated, diode-laser spectroscopy. The overall self-reaction rate constant expressed as the product of both a temperature dependent and water vapor dependent term is k = 7.8x10-14 (e(8.2±2.5kJ/mol)/RT) x (1 + (1.7 ± 0.2 x 10-30) x e(71.2 ± 17 kJ/mol)/RT [H2O]) suggesting formation of a β-HEP-H2O complex is responsible for the increase in the self-reaction rate coefficient with increasing water concentration. Complex formation is supported by computational results identifying three local energy minima for the β-HEP-H2O complex. As the troposphere continues to get warmer and wetter, more of the peroxy radicals will be complexed with water. Thus it is important to investigate the effect of water vapor on kinetics of other atmospherically relevant radicals and to determine the effects of these altered kinetics on tropospheric ozone concentrations.

Water vapor enhancement of peroxy radical reactions

249th National Meeting (2015)

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