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)

The thermal decomposition kinetics of a wide range of cluster ions in and n ear the low-pressure limit were modeled with a master equation analysis bas ed on an exponential up energy transfer model and an orbiting transition st ate. Cluster ion bond energies and helium-cluster ion energy transfer param eters were derived. Analysis of the temperature and pressure dependent deco mposition kinetics of a set of clusters, for which bond enthalpies have bee n measured, showed that the master equation approach reproduces the literat ure bond energies to better than 1 kcal mol(-1). The helium-cluster ion ene rgy transfer was found to be very efficient, resembling the predictions of ergodic collision theory. On the basis of the results of the modeling of th e calibration clusters, the analysis was extended to derive bond energies f or the important atmospheric cluster ions of the form HSO4-(H2SO4),(HNO3)(y ), ((x, y) = (1-5, 0), (0, 1-2), and (1, 1)).