Michael A. A. Clyne

Rate constants for specific product channels from metastable Ar(3P2,0) reactions and spectrometer calibration in the vacuum ultraviolet

The product channels from interaction of metastable argon atoms (3P2,0) with a series of chlorine containing molecules (Cl2, NOCl, ClO, HCl, CCl4, PCl3, and SnCl4), as well as some other molecules (Br2, N2O, NO2, H2S, and COS), have been investigated by emission spectroscopy. The rate constants for product channels were established by comparison of the emission intensities from the excited state products to the emission intensities from excited state Kr atoms, which have known rate constants for excitation by metastable argon atoms. Comparison of the individual product rate constants with previously determined total quenching rate constants of Ar(3P2,0) gave the branching ratios for emitting product channels. Although our measurements include the wavelength range from 120–800 nm, emphasis is placed upon the vacuum ultraviolet region and upon the ArCl*, ArBr*, and ArO* product channels. The highest ArCl* yield, ∼50%, was obtained for Cl2 and ClO. Quenching mechanisms for the halogen containing reagents are...

Laser-induced fluorescence of the BO and BO2 free radicals

Abstract The first observation of quantum-resolved laser-induced fluorescence of the BO free radical is described. The source of ground-state X 2 Σ + BO radicals was the reaction of BCl 3 with a mixture of O 3 P and N 4 S atoms in the absence of O 2 . Laser excitation spectra involving the vibrational levels 11 ⩾ ν′ ⩾ 0 of the A 2 Π state are reported, using excitation wavelengths varying from 425 nm down to 277 nm, from a YAG-pumped narrow-band dye laser. The radiative lifetime of BO A 2 Π (11 ⩾ ν′ ⩾ 0) was determined to be (1.7 6 ± 0.1 3 ) μs (1σ), based on fluorescence decay studied. Implications of this relatively long lifetime for lasing on the AX transition of BO are discussed. Quenching of BO A 2 Π by N 2 is relatively slow, with k N 2 −11 cm 3 molecule −1 s −1 . Laser excitation spectra of BO 2 radicals are reported from the reaction of O 3 P atoms with BCl 3 with O 2 present; no BO radicals were detected under these conditions. The radiative lifetime of the 002 vibronic level of BO 2 A 2 Π has been determined to be (182 ± 20) ns (1σ). Quenching of this excited level of BO 2 by O 2 is efficient.

Quantum-resolved dynamics of excited states. Part 4.—Radiative and predissociative lifetimes of IF B3Π(0+)

The kinetics of decay of excited IF B3Π(0+) molecules in defined ro-vibrational states (v′, J′) have been determined under collision-free conditions. Laser-induced fluorescence was used to directly determine the dynamics of excited IF(B); the laser bandwidth was 1 pm, using excitation wavelengths between 440 and 530 nm.Collision-free lifetimes τ0 were measured for all stable states of IF(B). The mean values text-decoration:overlineτ0(1σ) varied monotonically with v′ from (8.80 ± 0.89)µs (6 J′ 0) for v′= 9, down to (6.96 ± 0.47)µs (45 J′ 5) for v′= 0. The mean value of the electric dipole moment |Re|2 for the B–X transition was calculated to be (0.101 ± 0.010) D2.As for BrF(B), the higher-energy vibrational levels of IF(B) showed predissociation. This predissociation of IF in the states v′= 8, J′ 52 and v′= 9, J′ 7 was observed as a shortening of lifetime. All accessible rotational states in the (8,J′) and (9,J′) manifolds above the onset of predissociation had similar lifetimes near 1 µs. However, the (10,J′) manifold showed a rotationally dependent predissociation, with a nearly linear dependence of 1/τ0 upon J′(J′+ 1). The magnitudes of the predissociation energies in the (8,J′) and (9,J′) manifolds indicate that the predissociating state is a shallow, bound state [Herzberg case 1(b)]. Narrow limits for the (previously uncertain) dissociation energy of IF X1Σ+ can thus be obtained: D00(IF)=(22 333 ± 2) cm–1.The low-lying states of IF are considered in relation to the present and previous results. It is concluded that the predissociation of the (8,J′) and (9,J′) states is probably due to interaction of the B state with a weakly-bound 0+ state, designated here as C3Π(0+), which dissociates diabatically to I2P+ F2P½ atoms. Lifetime shortening is ascribed to interaction at long r-values of the bound C3Π(0+) state with a repulsive 0+ state, that correlates with I2P+ F2P atoms. The strong predissociation in IF(B) found previously at higher energies [in the (11, 45) and higher states] is due to direct interaction of the B state and the repulsive 0+ state. Similarities with BrF are indicated.

Electronic energy transfer from metastable argon atoms to krypton atoms

The interaction between metastable argon atoms (3P2,0) and krypton atoms has been studied at room temperature using the flowing afterglow technique. Measurements of the emission intensities from the excited‐krypton levels show that only Kr(5p[3/2]2) and Kr(5p[3/2]1) are primary products from Ar* (3P2). The pressure dependence of the emission intensities from other 5p krypton states shows that these are produced by collisional cascade from the 5p[3/2]2,1 levels; some rate constants for these cascade processes are reported. Absorption measurements using the 123.6 nm resonance transition of Kr demonstrate that the emitting Kr(5s 3P1) state carries no excess translational energy; therefore, it must be produced only via radiative cascade from Kr(5p) levels. Thus Ar (3P2) excitation rate constants of 5.6 and 0.65×10−12 cm3  molecule −1⋅sec−1 are established for excitation to Kr(5p[3/2]2) and Kr(5p[3/2]1), respectively. The Ar(3P2)+Kr reaction can serve as a reference for obtaining rate constants for excitation ...

Atomic resonance fluorescence for rate constants of rapid bimolecular reactions. Part 5—Hydrogen atom reactions; H + NO2 and H + O3

Direct determinations of the rate constants k1 and k2(cm3 molecule–1 s–1) are reported, for the reactions of H 2S atoms with NO2 and O3, using atomic resonance fluorescence in a discharge–flow system to detect hydrogen atoms. Measurements of k1 for reaction (1) at four temperatures from 298 to 653 K were made: H + NO2[graphic omitted] NO + OH; (1) the following overall Arrhenius expression was obtained: log10k1=(–9.319 ± 0.084)–(174 ± 31)/T(2σ). Measurements of k2 for reaction (2) were made at three temperatures between 298 and 638 K: H + O3[graphic omitted] O2+ OH.(2) These results gave the expression: log10k2=(–10.005 ± 0.102)–(224 ± 26)/T(2σ).

Radiative lifetimes of metastable states of free radicals. I. NF b 1Σ

Abstract Metastable excited NF b 1 Σ + radicals were generated by means of a pulsed Tesla discharge in a slowly-flowing dilute mixture of NF 3 or N 2 F 4 in argon. The excited NF radicals are believed to be generated by energy transfer between Ar 3 P 0,2 metastable atoms and NF 3 (or N 2 F 4 ). The decay of NF spontaneous emission near 530 nm, b 1 Σ + (υ′=0)-X 3 Σ(υ″=0), was used to determine the lifetime of NF b 1 Σ + . The results gave a radiative lifetime τ rad equal to (22.6±1.7)×10 −3 s (95% confidence limit). The square of the electronic transition moment | R e | 2 was calculated to be (2.1 ± 0.2)×10 −5 D 2 . Rate coefficients ( k M ) for quenching of NF b 1 Σ + were found to be k NF , = (1.8 ± 0.7) × 10 −12 cm 3 s −1 and k Ar −17 cm 3 s −1 . The method described here is expected to be useful for the study of other excited states whose lifetimes are inthe range 300 μs to 1 s.

B 3 Π(0+) states of IF, ICI and IBr. Part 1 —Calculation of the RKR turning points and Franck–Condon factors for the B–X Systems

Values of the spectroscopic constants for the B3Π(0+)–X1∑+ systems of IF, ICI and IBr have been evaluated and used to determine the RKR turning points for the B3Π(0+) and X1∑+ states of the iodine monohalides. The RKR potential functions have been used to calculate r-centroids and Franck–Condon factors for the B–X systems.

Theoretical treatment of the spontaneous predissociation of Br2, B 3Π(0u+)

The spontaneous heterogeneous predissociation of the B 3Π(0u+) state of bromine is discussed. Theoretical treatment of the heterogeneous interaction is presented, with emphasis placed on the role of the Franck–Condon principle in predissociation. Numerically generated vibrational wave functions are used to calculate predissociation probabilities for the B state. From these calculations the parameters of the repulsive potential responsible for the predissociation are determined, and this potential curve is identified as the 1Π(1u) state. Good agreement with experimental results was obtained with a 1Πu potential of the form U(R) = 1.594×104/R9.384. This crosses the B state curve between v′ = 4 and 5, which is two levels higher than indicated in previous work. The new 1Πu curve is compatible with other theoretical and experimental results.

Kinetic behaviour of OH X2Π and A2σ+ using molecular resonance fluorescence spectrometry

A method for the investigation of OH X2Π(v″= 0) radical kinetics in a discharge-flow system at 300 K, with detection of OH by molecular resonance fluorescence, using the OH A2Σ+–X2Π(0, 0) transition, is described. Quenching cross sections for OH A2Σ+(by H2O, N2, Ar and He) were determined from steady-state kinetic analysis, and the effects of electronic quenching on the kinetic measurements were shown to be unimportant. The intensity of resonance fluorescence, under the conditions used, varied in direct proportion to [OH, X2Π, v″= 0] up to concentrations of 5 × 1014 cm–3.The kinetics of decay of OH radicals near 120 N m–2 total pressure include second order (2) and first order wall (w) reactions, OH + OH [graphic omitted] H2O + O (2), OH [graphic omitted] products. (w) Two independent methods of determination of k2 are described, allowing for kw, and based on fitting of experimental data to computed concentration profiles derived from a reaction scheme incorporating the major elementary reactions which can affect [OH]. These methods gave values for k2(300 K, cm3 molecule–1 s–1) of (1.27 ± 0.21)× 10–12 and (1.50 ± 0.34)× 10–12, leading to a mean value from our results, k2=(1.4 ± 0.2)× 10–12. Consideration of the present and previous data for k2 leads to a proposed overall value k2=(1.7 ± 0.6)× 10–12 cm3 molecule–1 s–1 at 300 K.

Mass spectrometric determinations of the rates of elementary reactions of NO and of NO2 with ground state N4S atoms

Kinetic studies of the reactions of NO, (1) and of NO2, (2), with N 4S atoms have been made using direct mass spectrometric detection of N atoms in a discharge flow system. The rate constant k1(cm3 molecule–1 s–1) for the rapid reaction (1), N + NO [graphic omitted] N2+ O (1), has been determined with pseudo first-order kinetic analysis ([NO]0/[N]0 1). The mean value for k1 was (2.2 ± 0.2)× 10–11 at 298 K, and between 298 and 670 K, k1 was given by the expression (8.2 ± 1.4)× 10–11 exp[–(410 ± 120) K/T].Similar kinetic studies of the N + NO2 reaction, using pseudo first-order analysis with very large excesses of NO2([NO2]0/[N]0 > 80), showed the rate constant for this reaction to be an order of magnitude less than the literature value. However, at lower values of [NO2]0/[N]0, much greater apparent rate constants for the N + NO2 reaction were obtained, similar to those found previously. These high values are attributed to a rapid catalytic cycle capable of removing both N atoms and NO2, i.e., N + NO2 [graphic omitted] N2O + O (2A), O + NO2 [graphic omitted] NO + O2(3), N + NO [graphic omitted] N2+ O (1). Reactions (1)+(3) have the stoichiometry, N + NO2→ N2+ O2: No evidence was found from N2O yields in the N + NO2 reaction for any reactive channel involving N + NO2 other than reaction (2A). The results give a mean value for k2A equal to (1.4 ± 0.2)× 10–12 cm3 molecule–1 s–1 at 298 K.