Dimerhyphen;formation rate coefficients from measurements of terminal dimer concentrations in freehyphen;jet expansions

摘要

Dimer formations in free jets of rare gases are considered as a simple example of recombination processes. In order to extract values of the local recombinationhyphen;rate coefficientkffrom measurements of the terminal dimer mole fractionxA2, a suddenhyphen;freeze model is used. Of the several kinetic models considered, only Bunkerrsquo;s model of stabilization of virtual orbiting pairs by collisions with third bodies yields realistic values of the collision effectiveness. Procedures are developed for (1) predicting the terminal value ofxA2for given source conditions and knownkf, (2) deducingkffor given source conditions and measuredxA2, and (3) selecting appropriate source conditions for specifiedxA2and knownkf. Data for Kr, Ar, and Ne from six experimental studies and one computer study are correlated by a steric factor of 0.4 and an activation energy of 0.6 times the potentialhyphen;well depth egr;. The simplified relationxA2quest;0.5lsqb;nosgr;3(egr;/kTo)7/5(dast;/sgr;)2/5rsqb;5/3, wherenois the source number density,Tois the source temperature,dast; is the sourcehyphen;orifice diameter, sgr; is the zerohyphen;potential interaction radius, andkis Boltzmannrsquo;s constant, predicts terminal dimer mole fractions to an approximation suitable for technical applications. It is suggested that a critical value ofxA2, namely, about 0.01, is associated with the initiation of significant trimer formation.