Absolute Rate Coefficients and Branching Percentages for the Reactions of POxCly- + N (4S3/2) and POxCly- + O (3P) at 298 K in a Selected-Ion Flow Tube Instrument

Abstract

The absolute rate coefficients and product ion branching percentages at 298 K for the reactions of several POxCly- species with atomic nitrogen (N (4S(3/2))) and atomic oxygen (O (3P)) have been determined in a selected-ion flow tube (SIFT) instrument. POxCly- ions are generated by electron impact on POCl3 in a high-pressure source. O atoms are generated by quantitative titration of N atoms with NO, where N atoms are produced by microwave discharge on N2. The experimental procedure allows for the determination of rate coefficients for the reaction of the reactant ion with N (4S(3/2)) and O (3P) as well as with N2 and NO. None of the ions react with N2 or NO, giving an upper limit to the rate coefficient of <5 x 10(-12) cm3 molecules(-1) s(-1). POCl3- and POCl2- do not react with N atoms, giving an upper limit to the rate coefficient of <1 x 10(-11) cm3 molecules(-1) s(-1). The major product ion for POCl3- and POCl2- reacting with O involves loss of Cl from the reactant ion, accounting for >85% of the products. PO2- is a minor product (<or=4%) from POCl2- + O. Only PO2Cl- reacts with both N and O, directly giving PO2- and PO3- as major products. In addition, calculations of the structures and energies for PO2N, PO2N-, and NCl have been performed at the G3 level of theory to obtain estimates for the energetics of the PO2Cl- reactions. PO2-, PO3-, and PO2Cl2- are all unreactive with both N and O. Comparisons of the reactivity of POxCly- ions with O atoms are made to previous reactivity studies of these ions. In particular, routes that yield the very stable PO2- and PO3- ions are discussed.