The temperature dependence of ’’single collision’’ bimolecular beam–gas chemiluminescent reactions. I. Theory

Abstract

We consider a ’’single collision’’ bimolecular beam–gas chemiluminescent reaction in which a metal beam formed effusively intersects a tenuous atmosphere of oxidant gas (10−4 to 10−6 torr) resulting in the emission of visible radiation from excited electronic states of the reaction products. The kinetics of this beam–gas chemiluminescent reaction are studied in order to derive the relationship between the chemiluminescent intensity and the parameters of the beam–gas reaction. A formula is derived which relates the relative single collision chemiluminescent intensity to reactant mass and temperature, the enthalpy of vaporization or sublimation of the (metal) beam source material (ΔHsub, ΔHvap), and the Arrhenius activation energy (Eexp) for formation of products in particular, chemiluminescing, excited electronic states. The determination of the temperature dependence of the observed chemiluminescence provides an upper bound to ΔH vaporization (ΔHsub). If ΔH is accurately known through independent studies, and heat capacity data is available, Eexp may be evaluated. The significance of Eexp determined from chemiluminescence experiments is considered for metal beams with and without thermally populated internal states.