Investigation of OH dynamics in the argon sensitized pulse radiolysis of water vapor

Abstract

Articles you may be interested inAn investigation of collisional processes in a Dicke narrowed transition of water vapor in the 7.8 μ m spectral region by frequency down-chirped quantum cascade laser spectroscopy Reactions of OR radical were studied in systems containing 650-Torr Ar and from 0.5 to 9-Torr H 2 0 using the method of pulse radiolysis-absorption spectroscopy. It was found that initial concentrations of OH radical increased and the half-life for its loss decreased at higher water pressures. Dependence of OR half-life on OH concentrations occurs because homogeneous OR loss processes are second order in reaction intennediates, whose concentration increases with added H 2 0. rA contribution by water in chaperoning OR/OR and OH/H combination is also important. The kinetic scheme was examined with a Gear , integrator. A good fit of the experimental rate data was obtained using literature values for rate constants of OR + OR, OH + H, and H + H reactions, when experimental zero-time r absorbance values were converted to OR concentrations based on an extinction coefficient of 6.37 X 1 <r' 1 mol-I cm -I at 309.5 nm. Using the same extinction coefficient, an alternative empirical reduction of rate· data gives k (apparent bimolecular) for loss of OH at 650-Torr AT pressure of 5.06X 10-11 cm 3 molec-I S-I, consistent with literature rate constants within 10%. Dependence of OM yieJd on water concentration is interpreted on a two state model for , argon precursor, involving short-lived (resonance state) Ar· eP I and 3P I ) and longer-lived (metastable) Ar""" e p 2 and 3p o )' Adjustment of assumed initial Ar· and Ar" concentrations allowed predic1ion of measured Of{ conc,~ntrations within experimental error at aU water pressures studied.