Macroscopic extension of RRK and Weisskopf models of unimolecular evaporation

Université de Toulouse; UPS; Laboratoire Collisions Agrégats Réactivité, IRSAMC F-31062 Toulouse, France, EU and CNRS; UMR 5589 - F-31062 Toulouse, France, EU

^(a) j-m.lhermite@irsamc.ups-tlse.fr

Received: 17 September 2012
Accepted: 9 October 2012

Abstract

The macroscopic behavior of two microscopic unimolecular evaporation models is examined. The temperature dependences of bulk equilibrium vapor pressures deduced from the Rice-Ramsperger-Kassel (RRK) model and from the Weisskopf model, respectively, are compared. The bulk vapor pressures of sodium given by both models are compared, over a wide temperature range, with the experimental vapor pressures. The Weisskopf model is in better agreement with the experimental data than the RRK theory: from the melting temperature to the critical temperature (∼ 370 K–2500 K), the vapor pressures of sodium calculated using the Weisskopf model agree with experimental values within 2%, whereas the RRK theory leads to errors of more than 40%. The Weisskopf theory satisfying the detailed balance principle, whereas the RRK theory does not, may explain this result.