Ion-molecule rate constants and branching ratios for the reaction of N3++O2 from 120 to 1400 K

Photodissociation dynamics of N3+

The photodissociation dynamics of [Formula: see text] excited from its (linear) 3[Formula: see text]/(bent) 3A″ ground to the first excited singlet and triplet states is investigated. Three-dimensional potential energy surfaces for the 1A′, 1A″, and 3A′ electronic states, correlating with the 1Δg and 3Πu states in linear geometry, for [Formula: see text] are constructed using high-level electronic structure calculations and represented as reproducing kernels. The reference ab initio energies are calculated at the MRCI+Q/aug-cc-pVTZ level of theory. For following the photodissociation dynamics in the excited states, rotational and vibrational distributions P( v′) and P( j′) for the N2 product are determined from vertically excited ground state distributions. Due to the different shapes of the ground state 3A″ potential energy surface and the excited states, appreciable angular momentum j′ ∼ 60 is generated in diatomic fragments. The lifetimes in the excited states extend to at least 50 ps. Notably, results from sampling initial conditions from a thermal ensemble and from the Wigner distribution of the ground state wavefunction are comparable.

The N3+ Reactivity in Ionized Gases Containing Sulfur, Nitrogen, and Carbon Oxides

The N(3)(+) reactivity with SO(2), N(2)O, CO(2), and CO is studied by mass spectrometric techniques under a wide range of pressures from 10(-7) to 10(-4) Torr. The kinetics, reaction mechanism, and role of vibrationally excited ions are investigated by experimental and theoretical methods. Key distinguishing features of the N(3) (+) reactivity are evidenced by comparison to N(+) and N(2)(+) ions, which mainly undergo charge-exchange reactions. The N(+) transfer to SO(2) prompts formation of NO(+) ions and neutral oxides NO and SO. The N(+) transfer to N(2)O also leads to NO(+) ions by a process not allowed by spin conservation rules. In both cases no reaction intermediate is detected, whereas CO(2) and CO are captured to form the very stable NCO(2) (+) and NCO(+) ions. NCO(2)(+) ions are characterized for the first time as strongly bound triplet ions of NOCO and ONCO connectivity. DFT and CCSD(T) computations have been carried out to investigate the structural and energetic features of the NCO(2) (+) species and their formation process.

Kinetic Study of the Reaction Ca+ + N2O from 188 to 1207 K

Ion-molecule reactions involving metallic species play a central role in the chemistry of planetary ionospheres and in many combustion processes. The kinetics of the Ca(+) + N(2)O --> CaO(+) + N(2) reaction was studied by the pulsed multiphoton dissociation at 193 nm of organo-calcium vapor in the presence of N(2)O, followed by time-resolved laser-induced fluorescence spectroscopy of Ca(+) at 393.37 nm (4(2)P(3/2) <-- 4(2)S(1/2)). This yielded k(188-1207 K) = 5.45 x 10(-11) (T/300 K)(0.53) exp(282 K/T) cm(3) molecule(-1) s(-1), with an estimated accuracy of +/-13% (188-600 K) and +/-27% (600-1207 K). The temperature dependence of this barrierless reaction, with a minimum in the rate coefficient between 400 and 600 K, appears to be explained by the role of N(2)O vibrational excitation. This is examined using a classical trajectory treatment on a potential energy surface calculated at the B3LYP/6-311+g(2d,p) level of theory.

Reexamination of ionospheric chemistry: high temperature kinetics, internal energy dependences, unusual isomers, and corrections

A number of aspects of ionospheric chemistry are revisited. The review discusses in detail only work performed at AFRL, but other work is mentioned. A large portion of the paper discusses measurements of the kinetics of upper ionospheric reactions at very high temperatures, i.e. the upper temperature range has been extended to at least 1400 K and in some cases to 1800 K. These temperatures are high enough to excite vibrations in O2, N2, and NO and comparing them to drift tube data allows information on the rotational temperature and vibrational level dependences to be derived. Rotational and translational energy are equivalent in controlling the kinetics in most reactions. Vibrational energy in O2 and N2 is often found to promote reactivity which is shown to cause ionospheric density depletions. NO vibrations do not significantly affect the reactivity. In a number of cases, detailed calculations accompanied the experimental studies and elucidated details of the mechanisms. Kinetics of two peroxide isomers important in the lower ionospheric have been measured for the first time, i.e. NOO+ and ONOO-. Finally, two examples are shown where errors in previous data are corrected.

Rate constants for the reactions of CO3- and O3- with SO2 from 300 to 1440 K

Rate constants for the reactions of CO(3) (-) and O(3) (-) with SO(2) have been measured between 300 and 1440 K in a high temperature flowing afterglow apparatus. The CO(3) (-) rate constants near to the collision rate at low temperatures and fall by about a factor of 50 with temperature until a broad minimum is reached at 900-1300 K. The highest temperature point shows the increasing rate constant. Comparison to drift tube data taken in a helium buffer shows that total energy controls the reactivity, presumably because the reaction goes through a long lived complex even at 1440 K. The reaction of O(3) (-) with SO(2) was studied up to 1400 K. The rate constant is collisional until 700 K and then decreases with increasing temperature. Rate constants measured at 1300 and 1400 K appear to show an increase, but that observation is questionable since O(3) (-) could not be made cleanly. The O(3) (-) data at 1200 K and below show that total energy controls reactivity in that range.

Ion chemistry of NOO+

The kinetics for the reactions of NOO+ ions with neutral molecules having ionization potentials (IPs) from 9.27 to 15.58 eV was measured in a selected ion flow tube at 298 K. The NOO+ ions are produced from the reaction of N3+ + O2 and have been reacted with the following: NO, C6F6, CS2, CF3I, C3F6, OCS, C2H6, Xe, SO2, O3, N2O, CO2, Kr, CO, D2, and N2. Numerous types of reactions were observed with the various neutral reagents, including production of NO+ (which may involve loss of an O from the ion or addition of O to the neutral reactant, although the two channels could not be distinguished here), charge transfer, isomerization of NOO+ to ONO+, and hydride abstraction. High level theoretical calculations of the structures and energetics of the various isomers, electronic states, and transition states of NOO and NOO+ were performed to better understand the observed reactivity. All neutral species with an IP< or =11.18 eV were observed to react with NOO+ in part by charge transfer. Detailed calculations showed that the recommended adiabatic and vertical IPs of NOO are 10.4 and 11.7 eV, respectively, at the MRCISDQ/AVQZ level of theory. The observed experimental limit for charge transfer of 11.18 eV agreed well with the energetics of the final products obtained from theory if dissociation of the neutral metastable product occurred, i.e., the products were X+ +[O(3P) + NO(2Pi)], where [O(3P)+NO(2Pi)] formed via dissociation of metastable NOO. Charge exchange with neutral reagent X would, therefore, be exothermic if IP(X)<[IPad(NOO)-DeltaE(O+NO)-NOO]= approximately 11.1 eV, where IPad(NOO) is the adiabatic IP. The potential energy surface for the reaction of NOO+ with C2H6 was also calculated, indicating that two pathways for formation of HNO2 + C2H5 (+) exist.