Richard C. Oldenborg

Spectroscopy and reaction kinetics of HS radicals

Abstract A laser-induced fluorescence technique is used to monitor the HS radical concentration. The rate constants at room temperature have been determined for the reaction of HS radical with various added scavengers.

Quenching of oxalyl fluoride (3Au) molecules

Abstract Rate constants for quenching of oxalyl fluoride (3Au) molecules by selected classes of quenchers have been investigated using the technique of laser-induced time-resolved phosphorescence. Various inorganic, alkane, halogenated alkane, alkene, halogenated alkene, diene and alkyne quenchers were studied. NO was found to have a much larger quenching rate constant than O2 (6.8 × 1010 and 1.4 × 108 l mol−1 s−1 respectively). The alkane data are consistent with a hydrogen atom abstraction mechanism. Both alkene and halogenated alkene rate constants were found to increase as the triplet energy of the particular quencher decreased. Similar correlations of rate constants and triplet energy levels were found for the diene and alkyne compounds studied. The phosphorescence emission spectrum was recorded and the 3Au state of oxalyl fluoride was found to lie at 85.6 kcal mol−1. A single progression in the ground state ν1 (CO symmetric stretch) is the dominant feature of the spectrum.

UV laser photochemistry of CF2Br2

CF2Br2 has been irradiated at room temperature with KrF (248.4 nm) and ArF (193.3 nm) lasers. The fluorescence produced by the KrF laser irradiation appears to consist of only two ν2 progressions, v′2=6 and 5 for the CF2 (1B1−X 1A1) transition. The collision‐free lifetime of the CF2 emission was found to be 59 ns. The fluence dependence of the emission is quadratic. Upon irradiation of CF2Br2 with an ArF laser various emitting species were noted. Emission from CF(A 2Σ+–X 2Π), CF(B 2Δ–X 2Π), CF2(2B1–X 1A1), and Br2(3Πo+u–1Σ+ g) molecules was noted. Laser‐induced fluorescence excitation spectra confirmed the presence of CF2. The ArF laser fluence dependence of CF2(X 1A1) formation was found to be 1.0.

Laser‐induced fluorescence of gaseous UF6 in the A–X̃ band

The A–X band of gaseous UF6 has been studied using the laser‐induced fluorescence technique. Excitation and fluorescence spectra are presented for various pressures of UH6 at room temperature. The fluorescence spectra show little change over the pressure range 0.2–20 torr, with a peak wavelength at 421 nm. In contrast, the peak wavelength of the excitation spectra shows a noticeable shift from 391 to 385 nm when the UF6 pressure is increased from 2 to 20 torr. A Stern–Volmer plot of UF6 self‐quenching data shows a pronounced nonlinear behavior over this same pressure region. From an analysis of the laser‐induced fluorescence spectra, we develop a simple kinetic model for UF6 excited‐ state dynamics. A standard kinetic treatment of this scheme yields a prediction for the dependence of the fluorescence decay lifetime on total pressure that is in good agreement with experimental results.

Laser-induced time-resolved emission of electronically-excited UF6☆

Abstract Lifetimes of electronically excited UF6 molecules have been determined at room temperature from 0.01–80 torr. An estimate for the collision free lifetime ⪕40 μs for UF6 excited at 393 nm was determined. The Stern—Volmer plots for UF6 self-quenching revealed from regions of curvature.

Optically pumped NO (A 2Σ+→X 2π) ultraviolet laser

Lasing action on the (0,1) and (0,2) γ bands of NO at 237 and 248 nm, respectively, has been obtained by longitudinal pumping of 0.5 Torr of NO on the (0,0) γ‐band transition at 227 nm. Typical output pulse energies were 13 μJ at an intrinsic energy conversion efficiency of approximately 15%.Lasing action on the (0,1) and (0,2) ..gamma.. bands of NO at 237 and 248 nm, respectively, has been obtained by longitudinal pumping of 0.5 Torr of NO on the (0,0) ..gamma..-band transition at 227 nm. Typical output pulse energies were 13 ..mu..J at an intrinsic energy conversion efficiency of approximately 15%.

Quenching of electronically-excited UF6 emission by selected organics☆

Abstract Rate constants at 25°C have been evaluated for the quenching of electronically excited UF6 by selected organic molecules. Values for the rate constants at 25°C (units of 1011 ρ/mole s) for CH4, C2H6, C2F6, CHF2CHF2, C2H2, and C2H4 are 0.061, 3.8, 0.022, 0.072, 6.0, and 5, respectively.

Characterization of several ultraviolet–visible emission lines from a lead hollow-cathode lamp

The Fourier-transform spectra (0.015-cm−1 resolution) of the nonresonant 405.8-, 368.4-, and 364.0-nm lines and the resonant 283.3-nm line from a lead hollow-cathode lamp are reported. The splittings for the various isotopic and nuclear hyperfine transitions for all four lines are found to be consistent with previous measurements and assignments. At the recommended lamp operating current of 4 mA, all peak shapes within all four lines studied were satisfactorily fitted with Gaussian functions corresponding to the same Doppler temperature of 750 ± 30 K, indicating no significant self-absorption of the 283.3-nm resonant line. At a much-elevated lamp current the peaks for the nonresonant lines are increased in intensity and slightly broadened, whereas the peaks for the resonant line have approximately the same intensity as at 4 mA but are no longer Gaussian shaped.

Spectra and modeling of laser‐induced emission from multiple‐photon (λ=248.4 nm) irradiation of UF6

The laser‐induced emission from KrF‐laser irradiation of gaseous, room temperature UF6 has been studied as a function of time, wavelength, pressure, and laser fluence. Spectra in the 200–900 nm region are presented at several sampling times. One group of 17 emission peaks in the 650–900 nm range has been assigned to the 3Γ6→1Γ7 transition in UF5. A possible kinetic mechanism is presented that is qualitatively consistent with the time‐resolved emission data over the experimental pressures and laser fluences investigated.

Quenching of electronically-excited UF6 by selected inorganics

Abstract Rate constants at 25°C have been evaluated for the quenching of electronically-excited UF 6 by selected inorganic molecules. Values for the rate constants at 25°C (units of 10 11 ρ/mole s) for O 2 , N 2 , and Ar are 1.0, 0.025, and 0.0097, respectively. N 2 and Ar quenching exhibit a saturation effect at high pressures and their rate constants were evaluated from low pressure data where the quenching follows a linear Stern-Volmer relationship.