J. L. Durant

Collisional electronic quenching of NO A 2Σ+ by N2 from 300 to 4500 K

We report rate coefficients for electronic quenching of NO A 2Σ+ v’=0 by N2 measured at room temperature and at high temperatures behind reproducible shock waves. The quenching cross section increases from 0.007 A2 at 300 K to 7 A2 at 4500 K, and the temperature dependence in the range 300–2300 K is best understood using a charge‐transfer (harpoon) collision model. We also record dispersed fluorescence spectra and time‐resolved fluorescence from both the directly pumped level (v’=0) and a collisionally populated level (v’=1); from these results we obtain rate coefficients for vibrational energy transfer in NO (A) and electronic quenching of v’=1 at 1900 K.

Collisional electronic quenching rates for NO A2Σ+ (ν = 0)

Abstract We report rate coefficients for electronic quenching of NO A2Σ+ (ν = 0) by CO, CO2, H2, H2O, O2, NO, N2O, NO2, and Ar measured at room temperature and at elevated temperatures behind reproducible shocks. The magnitudes of the rates and the observed temperature dependencies of NO A2Σ+ quenching by these collision partners are found to be in accord with a charge-transfer (harpoon) collision model for the process.

Collisional electronic quenching of OH A 2Σ (v’=0) measured at high temperature in a shock tube

Rate coefficients are reported for electronic quenching of OH A 2Σ v’=0 by N2, O2, CO, CO2, NO, Ar, Kr, and Xe measured at high temperatures behind reproducible shock waves. The cross section for quenching by Ar was found to be less than 0.06 A2. The cross sections for quenching by N2 and Kr were found to be 0.5 and 1.0 A2, respectively. The cross sections for the remaining species were found to be of order gas kinetic. For all of the species the cross sections were found to be very weak functions of temperature from 1900 to 2300 K. The measured cross sections are compared with previous measurements at lower temperatures. The observed variation with species and with temperature is observed to be consistent with a charge‐transfer model for the process.

Electronic quenching rates for NO(A 2Σ+) measured in a shock tube

Abstract We report rate coefficients for electronic quenching of NO(A 2Σ+) by NO(X 2Π), CO2, Ar and He measured at high temperature behind reproducible shock waves. NO and CO2 are efficient quenchers at temperatures between 300 and 2100 K while the rare gases quench much less efficiently. We develop a model to predict the temperature dependence of NO(A 2Σ+) quenching by collision partners that have a large electron affinity and thereby enable a charge-transfer complex (NO+X−) to mediate the transition between the A 2Σ+ ν′ =0 and X 2Π states of NO.

The electric dipole moment of NO A 2Σ+ v’=0 measured using Stark quantum‐beat spectroscopy

We report measurements and analysis of Stark quantum beats observed in the fluorescence of nitric oxide (NO) from which we determine the electric dipole moment of the A 2Σ+ v’=0 state. A pulse‐amplified cw dye laser was used to excite the A–X (0,0) Q1(1) transition of 14N16O in electric fields up to 22.5 kV/cm. Fourier analysis of the time‐resolved laser‐induced fluorescence signals yielded Stark tunings for each of the six ‖MF‖ hyperfine sublevels in the N=1, J=3/2 spin‐rotational level. The measurements were fit to a model Hamiltonian including fine, hyperfine, and Stark matrix elements. The resulting dipole moment was then corrected for polarizability effects to yield a value for the A 2Σ+ v’=0 state of μA=1.08±0.04 D. This result compares favorably to a previous measurement of μA in v’=3 and to our quantum theoretical calculations of the A 2Σ+ v’=0 state reported here.

Near‐resonant electronic energy transfer in the electronic quenching of NO A 2Σ+ by hydrocarbons and ammonia

We report rate coefficients for the electronic quenching of NO A 2Σ+ v=0 by several hydrocarbon fuel gases, methane, ethane, propane, ethene, and ethyne, and by ammonia over a wide temperature range (300–2300 K). High temperature data is obtained behind reproducible shock waves. High‐temperature quenching of NO by many species has previously been explained by a charge‐transfer (harpoon) model. However, we find such a model unable to explain a portion of the quenching behavior reported here. Instead, we propose that a near‐resonant electronic energy transfer mechanism is active.

The reaction of NH2 (X 2B1) with O (X 3P): A theoretical study employing Gaussian 2 theory

The ground 2A‘ and excited 4A’ surfaces for the reaction of NH2 (X 2B1) with O (X 3P), have been characterized by calculating energies, geometries, and frequencies for all important stationary points connecting reactants and products. The Gaussian 2 methodology was used for all calculations with further refinement for transition state properties made by calculating energies using QCISD/6–311G(d,p) geometries and frequencies. The results predict that, on the 2A‘ surface, an H2NO intermediate is formed which is 87.6 kcal/mol below the separated NH2+O reactants. This intermediate may either fragment to form H+HNO or H2+NO, or undergo a 1,2 hydrogen shift to form trans‐HNOH. This second intermediate may dissociate to either NH+OH or H+HNO, or isomerize to cis‐HNOH which, in turn, may dissociate into the same products. The abstraction reaction NH2+O→NH+OH was found to have a transition state 6.7 kcal/mol above the energy of the separated reactants.