Highly vibrationally excited n-propylbenzene cations, C 9 H 12 + *, were prepared by the charge transfer reaction O 2 + + C 9 H 12 f O 2 + C 9 H 12 + * in a turbulent ion flow tube. The subsequent competition between fragmentation of C 9 H 12 + * into C 7 H 7 + + C 2 H 5 and stabilization in collisions with N 2 was studied at temperatures in the range 423-603 K and at pressures between 15 and 200 Torr. Most of the C 7 H 7 + is the aromatic benzylium isomer, while the fraction of the minor species, seven-membered-ring tropylium, increases with T, from 5 to 20%. Minor fragments are C 6 H 6 + , C 7 H 8 + , and C 8 H 9 + . Energy-transfer step sizes 〈∆E〉 for collisional deactivation are obtained by combining the stabilization versus fragmentation ratios measured as a function of pressure in this study with fragmentation rates from the literature. The values are compared with related information for other excited molecular ions and are similar to those of their neutral analogues. At the highest temperatures, C 9 H 12 + was also observed to pyrolyze after collisional stabilization. Employing unimolecular rate theory, the derived rate constants for thermal dissociation of C 9 H 12 + are related to values derived from the specific rate constants k(E,J) for fragmentation. Good agreement is found between measured and predicted pyrolysis rate constants. This allows us to confirm the dissociation energy of C 9 H 12 + into C 7 H 7 + (benzylium) and C 2 H 5 as 166.9 ((2.2) kJ mol -1 (at 0 K).

Rate constants and product ion branching fractions for the gas-phase reactions of O2 and O3 with the anions (a) PO2Cl-, (b) POCl3 -, (c) POCl2 -, and (d) PO2Cl2 - 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 PO2Cl- reacts with O2 to a measurable extent, having k(163−400 K) = 1.1 × 10-8(T/K)-1.0 cm3 molecule-1 s-1, while O3 reacts with all of the anions except PO2Cl2 -. The fitted rate constant expressions for the O3 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 cm3 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 PO2Cl- with O2 and O3 yield predominantly PO3 - and PO4 -. The reaction of POCl2 - with O3 yields mostly Cl- and PO2Cl2 -, while the POCl3 - reaction with O3 yields mostly O3 - and PO2Cl2 -.

Rate coefficients for the depletion of ground-state nitrogen atoms by O2 have been measured using a high-temperature photochemistry reactor. The N atoms were generated by VUV flash photolysis of N2O, and the relative concentrations were monitored by resonance fluorescence. The data are best fitted by the expression k(400−1220 K) = 2.0 × 10-18(T/K)2.15 exp(−2557 K/T) cm3 molecule-1 s-1 with 2σ precision limits varying from ±7% to ±20% depending upon temperature, and corresponding 2σ accuracy limits of ±23% to ±30%. Good agreement is found with earlier, electrical discharge initiated, rate coefficient measurements for the 280−910 K domain. Semiempirical theory-based calculations are presented that lead to a plot nearly indistinguishable from those of the present results and the Baulch et al. recommendation for the 300−5000 K temperature range. These yield a classical barrier E 0 ⧧ of 27.4 kJ mol-1. No reaction with CO2 could be observed; upper limit rate coefficients were obtained from 285 to 1140 K. These upper limits indicate that the reverse reaction is insignificant for models of nitrate ester and nitramine propellant dark zones.