Reaction Kinetics of PO₂Cl⁻, PO₂Cl₂⁻, POCl₂⁻, and POCl₃⁻ with O₂ and O₃ from 163 to 400 K

Rate constants and product ion branching fractions for the gas-phase reactions of O 2 and O 3 with the anions (a) PO 2 Cl -, (b) POCl 3 -, (c) POCl 2 -, and (d) PO 2 Cl 2 - were measured in a selected-ion flow tube (SIFT). The kinetics were measured at temperatures of 163−400 K and a He pressure of 0.4 Torr. Only PO 2 Cl - reacts with O 2 to a measurable extent, having k (163−400 K) = 1.1 × 10 -8 ( T /K) -1.0 cm 3 molecule -1 s -1, while O 3 reacts with all of the anions except PO 2 Cl 2 - . The fitted rate constant expressions for the O 3 reaction with anions a−c are as follows: k a (163−400 K) = 3.5 × 10 -6 ( T /K) -1.6, k b (163−400 K) = 4.0 × 10 -7 ( T /K) -1.2, and k c (163−400 K) = 3.7 × 10 -7 ( T /K) -1.4 cm 3 molecule -1 s -1 . Calculations were performed at the G3 level of theory to obtain optimized geometries, energies, and electron affinities (EAs) of the reactant and product species, as well as to determine the reaction thermochemistry to help understand the experimental results. The PO x Cl y - anions that have lower electron binding energies (eBE) and higher spin multiplicities are more reactive. The doublets are more labile than the singlets. How the extra electron density is distributed in the anion does not predict the observed reactivity of the ion. The reactions of PO 2 Cl - with O 2 and O 3 yield predominantly PO 3 - and PO 4 - . The reaction of POCl 2 - with O 3 yields mostly Cl - and PO 2 Cl 2 -, while the POCl 3 - reaction with O 3 yields mostly O 3 - and PO 2 Cl 2 - .