S.V. Filseth

Collisional Deactivation of O(1S)

Absolute rate coefficients for the collisional deactivation of O(1S) have been measured for CO2, CO, SF6, O2, H2O, NH3, CH4, C2H4, C2H6N2O, NO, NO2, H2, N2, He, Ne, Ar, Kr, and Xe. The measurements have been made with a lifetime technique in which O(1S) is produced in the photodissociation of CO2 by a pulsed vacuum‐ultraviolet light source The rate coefficients were obtained from time‐resolved measurements of the intensity of the O(1S → 1D) line at 5577 A. Deactivation of O(1S) by collision induced radiation has been observed for H2, N2, Ar, Kr, and Xe.

Absolute rate constants for the reactions of CH(X2II) with NO, N2O, NO2 and N2 at room temperature

Abstract The reaction of CH with N 2 is the initial step in what is thought to be one of the principal mechanisms for the formation of nitrogen oxides in flames, and reactions of CH with these oxides also influence the final composition of the burnt gases. In order to study these reactons, we produced CH radicals by infrared multiple photon dissociation (pulsed CO 2 laser) of CH 3 NH 2 , CH 3 CN, and cyclo-C 3 H 6 . The subsequent removal of CH by reaction with NO, N 2 O, NO 2 and N 2 was observed by laser induced fluorescence. For the first three reactions, the rates at 300 K are fast: k NO = (2.0 ± 0.3) × 10 −10 cm 3 s −1 k N 2 O = (7.8 ± 1.4) × 10 −11 cm 3 3 s −1 , and k NO 2 = (1.67 ± 0.11) × 10 −10 cm 3 s −1 . The reaction with N 2 is endothermic and the observed pressure-dependent rate constants at 300 K are interpreted in terms of a collision-stabilised recombination mechanism, for which we estimate the limiting low press-are rate constant k 3 = (2.6 ± 0.3) × 10 −31 cm 6 s −1 and the high pressure rate constant k 2 = (6.3 ± 1.3) × 10 −13 cm 3 3 −2 .

Absolute rate constant for the reaction of CH with O2

Abstract CH(X3II) has been produced in the multiple-photon dissociation of methylamine by a TEA CO2 laser. Laser-induced fluorescence has been used to measure relative CH concentrations as a function of time and added gas pressures. Chemiluminescence which accompanies the reaction is due to the production of OH(A 2Σ+) in the reaction. The rate constant obtained from the fluorescence experiments is (3.3 ± 0.4) × 10−11 cm3 molecule−1 s−1 at 298 K, in agreement with that deduced from the chemiluminescence signal.

Erratum: Flash Photolytic Production, Reactive Lifetime, and Collisional Quenching of O2(b 1Σg+, v′=0)

Collisional quenching of O2(b 1Σg+, υ′ = 0) at room temperature by O2 and a variety of foreign gases has been investigated with a pulsed lifetime measurement technique. O2(b 1Σg+, υ′ = 0) has been produced in a pulsed mode through flash photolysis of O2 in the vacuum uv and has been detected through the emission of the (0, 0) band at 7620 A of the forbidden O2(b 1Σg+ → X 3Σg− transition. The (0, 0) band intensity has been measured as a function of time after the photolysis flash and as a function of the O2 and foreign gas pressures. Quenching rate constants are derived from the reactive lifetimes. The photolytic production of O2(b 1Σg+, υ′ = 0) from O2 and the quenching by O2 has been studied at O2 pressures from 0.02–100 torr. The observations at low O2 pressures from 0.02 to about 1 torr are consistent with the previously established fast O2(b 1Σg+) production mechanism, O2 + hν → O(1D) + O(3P), O(1D) + O2(X 3Σg−) → O(3P) + O2(b 1Σg+), in the Schumann–Runge continuum region. No emission of the (1, 1) an...

Absolute rate constants for the reactions of CH with O and N atoms

CH(X 2R) was produced by multiple infrared photon dissociation of CH3OH in the presence of excess atomic oxygen or nitrogen. Time‐resolved measurements of relative CH concentrations were made at 298 K with a tunable dye laser. Rate constants deduced from the dependence of CH decay rate on atom concentration are (9.5±1.4)×10−11 cm3 s−1 for CH+O and (2.1±.5)×10−11 cm3 s−1 for CH+N.

Photodissociation of ICN at 351, 337, and 308 nm. Rotational and vibrational energy disposal in CN(X2Σ+)

Abstract The rotational and vibrational population distributions of CN(X 2 Σ + ) produced in the photodissociation of ICN vapor have been measured by the technique of laser-induced fluorescence. The distributions were obtained at 351, 337 and 308 nm where production of electronically excited fragments is not energetically possible. The average energy disposal in rotation of CN(X 2 Σ + , υ = 0) increases as the photon energy increases and is ≈ 16% of the available energy. For vibrationally excited CN which is produced at 308 nm, the rotational energy corresponds to 30 and 33% of the available energy for υ = 1 and 2 respectively. Energy disposal in vibration was measured at 308 nm and the fractional vibrational populations were found to be 2, 10, and 88% for υ = 2, 1 and 0 respectively. Measurements of the absorption coefficient of ICN at 337 and 351 nm were obtained, relative to that at 249 nm. Our rotational and vibrational distributions are compared with other studies of ICN and with applicable theory.

Direct measurement of thermal rate constants for state‐to‐state rotational energy transfer in collisions of CN(X 2Σ+, v=2, N) with He

Stimulated emission pumping state preparation and laser induced fluorescence state detection in the CN(B 2Σ+–X 2Σ+) violet system have been employed to study relaxation of single rotational states of CN(X 2Σ+, v=2) in collisions with He at 295 K. Approximately 2/3 of the value of the total removal rate constant for CN(X 2Σ+, v=2, N=2, 11, or 14) corresponds to changes in the rotational quantum number of ‖ΔN‖≤3 and a strong propensity is evident which favors even changes in N for ‖ΔN‖≤4. The measured rate constants are consistent with detailed balance, can be described with statistical power‐gap and exponential energy‐gap fitting functions and, where compared, are in accord with an IOS‐based scaling function. No significant difference is found between a sum of state‐to‐state rate constants and separately measured total removal rate constants for N=2, 11, and 14. The total removal rate constants decrease monotonically between N=0 and N=41 to about 1/3 of their value at N=0.

Photodissociation of BrCN and ICN in the a continuum: Vibrational and rotational distributions of CN(X 2Σ+)

Abstract We report results of experiments on photodissociation of ICN and BrCN in the long-wavelength (A) continuum in which primary rotational and vibrational distributions of CN in its electronic ground state are determined. For the CN fragment from ICN, our observations at 222 and 249 nm, reported here, together with our earlier results at longer wavelengths, show that the fraction of energy which goes into rotation (in the ground-state channel) is very nearly independent of exciting wavelength in the range 222–351 nm. This holds for each of CN vibrational levels 0, 1, and 2, where the fractions are 15, 25, and 33% respectively. The vibrational distributions decrease monotonously with υ, but show little change as a function of exciting wavelength. CN distributions are also presented for the photodissociation of BrCN at 193, 222, 249, and 308 nm. Results for both parent molecules are briefly discussed in relation to other recent experimental and theoretical work.

Quenching of C2(a 3Πu) produced in an intense infrared laser field

Abstract C 2 (a 3 Π u ) has been produced in the multiple-photon dissociation of acrylonitrile, C 2 H 3 CN, by a TEA CO 2 laser. Laser-induced fluorescence has been used to determine time-resolved relative C 2 concentrations in the presence of added Ar and O 2 and second-order rate constants of 2 × 10 −15 and 3.4 × 10 −12 cm 3 molecule −1 5 −1 have been obtained for these two quenchers, respectively. Vacuum-ultraviolet chemiluminescence is observed in the quenching by O 2 .

Rotation‐Vibration Energy Transfer in Collisions between OH(A 2Σ+) and Ar and N2

Collisional relaxation of OH(A 2Σ+, υ′, K′) in high rotational levels of υ′ = 0 and 1 has been investigated with respect to transitions from rotational levels in υ′ = 0 to levels in υ′ = 1. Initial nonequilibrium rotational distributions of OH(A 2Σ+) in υ′ = 0 and 1 were produced by monochromatic photodissociation of H2O with the radiation of a krypton resonance lamp at 1236 and 1165 A. The effect of added foreign gases (Ar and N2) on the population of individual levels in υ′ = 0 and 1 has been studied under steady‐state conditions by observing the emission intensities of individual lines in the (0, 0) and (1, 1) bands of the OH(A 2Σ+→X 2Π) transition. The essential observation was made on the population of the rotational level K′ = 15 in υ′ = 1. The population of this level increased significantly in the presence of Ar and N2 beyond the initial population produced from H2O alone. In comparison, the population of adjacent levels remained relatively unchanged or decreased when foreign gas was added. The ef...