Michael F. Golde

Quenching of metastable Ar, Kr, and Xe atoms by oxygen‐containing compounds: A resonance fluorescence study of reaction products

Quenching of electronically excited Ar, Kr, and Xe(3P0,2) atoms by diatomic and triatomic oxygen‐containing compounds has been studied by atomic resonance fluorescence in a discharge‐flow system at room temperature. Absolute branching ratios for molecular fragmentation in the quenching reactions have been obtained, showing that this channel is dominant in many cases. While single R–O bond cleavage is usually the favored process, cleavage of both bonds of H2O occurs in nearly 50% of quenching collisions with Ar*, and evidence is obtained for analogous atomization of NO2 and SO2 by Ar*. Emission by electronically excited fragment species has been found to be mostly weak; thus, dissociative excitation is a minor channel except for the reactions of Ar* with N2O and H2O.

Product distributions in the reactions of excited noble‐gas atoms with hydrogen‐containing compounds

The products of the reactions of electronically excited Ar(3P0, 3P2), Kr(3P2), and Xe(3P2) atoms with the chloromethanes, chlorofluoromethanes, CF3H, CF2HCl, CFHCl2, CF2Cl⋅CF2Cl, CF3⋅CCl3, and HCl have been investigated by the discharge‐flow technique, using atomic resonance fluorescence to probe dissociation channels and emission spectroscopy. Energy transfer leading to cleavage of C–H or C–Cl bonds is extremely efficient, particularly in the reactions of Xe(3P2) with CF2Cl2 and CFCl3 and of Ar(3P0, 2) with CFCl3, in which more than two Cl atoms are released per primary reactive event. The observation of contrasting behavior in the reactions of Xe(3P2) with CF3H and CF4 has led to the discovery of a qualitative correlation between the rate constants, the products of the energy transfer process, and the accessibility of dissociative or ionizing states of the reagent molecule, as revealed by its vacuum UV absorption spectrum.

Electron-ion recombination rate coefficient measurements in a flowing afterglow plasma

Abstract The flowing-afterglow technique in conjunction with computer modelling of the flowing plasma has been used to determine accurate dissociative-recombination rate coefficients α for the ions O2+, HCO+, CH5+, C2H5+, H3O+, CO2+, HCO2+, HN2O+, and N2O+ at 295 K. We find that the simple form of data analysis that was employed in earlier experiments was adequate and we largely confim earlier results. In the case of HCO+ ions, published coefficients range from 1.1 × 10−7 to 2.8 × 10−7 cm3/s, while our measurements give a value of 1.9 × 10−7 cm3/s.

Absolute rate constant for the O + NO chemiluminescence in the near infrared

Infrared chemiluminescence from the process O + NO (+ M) → NO2 + h ν (+ M) has been studied between 1.3 and 4.1 μm. The wavelength dependence of the continuum between 1.3 and 3.3 μm is in fair agreement with previous studies and the measured radiative rate constant at 1.51 μm, I1.510 = I1.51 / [O][NO], of (2.4 ± 0.8) × 10−17 cm3 sec−1 · μm−1 establishes the NO–O glow in this spectral range as a secondary emission standard. Comparison with previous studies of the visible region of the glow implies that the over‐all radiative rate constant Io lies in the range (9.4–11.2) × 10−17 cm3 sec−1. In the region 3.3–4.1 μm, the previously observed broad band, peaking at 3.7 μm, shows a complex kinetic dependence on [O] and [M].

Rate constants for electronic quenching of N2(A 3Σ+u, v=0–6) by O2, NO, CO, N2O, and C2H4

Rate constants for the title reactions have been measured using the discharge‐flow technique, with N2(B 3Πg –A 3Σ+u) laser‐excited fluorescence detection. C2H4 is an efficient quencher and exhibits little dependence of rate constant on vibrational quantum number v in N2(A). The rate constants for NO, O2, and N2O increase with v at low v, but are nearly independent of v for v≥3. CO shows a very strong dependence, with a peak in the rate constant at v=2 and a trough at v=5. These are the first data for the reactions of N2(A, v=2–6) with N2O. The other data are compared with previous measurements and discussed in terms of models of electronic‐to‐electronic energy transfer.Rate constants for the title reactions have been measured using the discharge‐flow technique, with N2(B 3Πg –A 3Σ+u) laser‐excited fluorescence detection. C2H4 is an efficient quencher and exhibits little dependence of rate constant on vibrational quantum number v in N2(A). The rate constants for NO, O2, and N2O increase with v at low v, but are nearly independent of v for v≥3. CO shows a very strong dependence, with a peak in the rate constant at v=2 and a trough at v=5. These are the first data for the reactions of N2(A, v=2–6) with N2O. The other data are compared with previous measurements and discussed in terms of models of electronic‐to‐electronic energy transfer.

Study of the products of the reactions of N2(A3Σu+): The effect of vibrational energy in N2(A)

Abstract The reactions of electronically excited N 2 (A 3 Σ u + ) molecules with selected small molecules have been studied in a discharge-flow system. A method is described for probing, with high sensitivity, the dependence of total quenching rate constants and reaction pathways on vibrational energy in the N 2 (A) state. Highly characteristic behavior is observed in the reactions with NH 3 , CH 3 OH, NO and O 2 .

Measurement of the absolute yield of CO(a 3Π)+O products in the dissociative recombination of CO2+ ions with electrons

A flowing-afterglow technique is described for measuring the absolute yield of a radiative product state from ion–electron recombination. The technique is applied to CO2++e− dissociative recombination. The measured yield of CO(a 3Π)+O(3P) is 0.29±0.10. This includes cascade from higher triplet states of CO. The vibrational distribution in CO(a 3Π,v=0–3) is approximately Boltzmann, with an effective temperature of 4200±300 K. The measured rate constant for quenching of CO(a) by CO2 is (1.0±0.2)×10−11 cm3 s−1, somewhat lower than previous measurements.

Chemiluminescence of argon bromide. I. The emission spectrum of ArBr

In this first systematic study of the ArBr molecule, chemiluminescence spectra are generated by the reactions of metastable argon atoms with bromine‐containing compounds. Three continua, due to the B (1/2)−X (1/2), B (1/2)−A (1/2) and C (3/2)−A3/2) transitions are characterized, their pressure dependences examined, and the extent of their overlap discussed in some detail. From the temperture dependence of the spectra, an upper limit for the electronic energy of the B (1/2) state is derived: TeB?61 850 cm−1.

Experimental study of the reactions of N2(A 3Σ+u) with H atoms and OH radicals

The reactions of N2(A 3Σ+u) with H atoms and OH radicals have been studied by the discharge‐flow technique. The concentrations of the radicals were measured by resonance fluorescence and N2(A) was monitored by (A−X) emission. The rate constant of the N2(A)+H reaction was measured as (2.1±0.3)×10−10 cm3 s−1. Chemical reaction to NH+N was shown to be unimportant. The total rate constant for quenching of N2(A) by OH was measured as (1.1±0.4)×10−10 cm3 s−1. The channel leading to OH(2Σ+) has a rate constant of (1.0±0.3)×10−10 cm3 s−1. Approximately 16% of the OH(A) is formed in v’=1. The mechanisms of these two very rapid reactions are discussed.

Chemi‐ionization reactions of metastable Ar(3P0,2) atoms

Using a discharge‐flow system and the saturation ion‐current technique, branching fractions for chemi‐ionization of a wide range of reagents by electronically‐excited Ar(3P0,2) atoms have been measured. In contrast to excited He and Ne atoms, ionization by excited Ar atoms is in no case the dominant channel, most branching fractions lying in the range 0.1 to 0.4. Significantly lower branching fractions are shown by the three reagents Cl2, Br2, and NO2 with the largest electron affinities. The results are discussed in terms of the charge transfer model for electronic quenching.