Pressure effects on the relaxation of an excited hydrogen peroxyl radical in an Argon bath

Molecular dynamics simulations were used to study the effect of pressure on the vibrational deactivation of HO2 embedded in an Ar bath gas at 800 K and at pressures ranging from 10 atm to 400 atm. The time dependent decay of vibrational energy is found to be poly-exponential for all of the simulated pressures. Plots of the relaxation rate constants as a function of density show deviation from the expected linear de-pendence at similar to 250 atm. A combinatorial multi-bath-gas collisional model suggests this deviation is due to the breakdown in the isolated binary collision approximation. Comparisons to studies with similar findings and additional considerations for understanding this behavior are discussed. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.