Cluster Ion Thermal Decomposition (II): Master Equation Modeling in the Low-Pressure Limit and Fall-Off Regions. Bond Energies for HSO4-(H2SO4)x(HNO3)y

Abstract

The thermal decomposition kinetics of a wide range of cluster ions in and near the low-pressure limit were modeled with a master equation analysis based on an exponential up energy transfer model and an orbiting transition state. Cluster ion bond energies and helium-cluster ion energy transfer parameters were derived. Analysis of the temperature and pressure dependent decomposition kinetics of a set of clusters, for which bond enthalpies have been measured, showed that the master equation approach reproduces the literature bond energies to better than 1 kcal mol-1. The helium-cluster ion energy transfer was found to be very efficient, resembling the predictions of ergodic collision theory. On the basis of the results of the modeling of the calibration clusters, the analysis was extended to derive bond energies for the important atmospheric cluster ions of the form HSO4-(H2SO4)x(HNO3)y, ((x, y) = (1−5, 0), (0, 1−2), and (1, 1)).