W. W. Rice

Laser-induced fluorescence excitation spectra of CCl2 and CFCI radicals in the gas phase

Abstract Laser-induced fluorescence excitation spectra in the gas phase have been obtained for CCl 2 and CFCI radicals. The observed spacings in the excitation spectra reported here agree well with previous absorption work in the matrix.

Reactions of CCl, CCl2 and CClF radicals

Abstract The rate constants at room temperature have been determined for the reaction of CCl, CCl 2 , and CClF radicals with various added scavengers. We have employed the technique of laser-induced fluorescence to permit the evaluation of these rate constants.

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.

UV laser photochemistry of CCl4 and CCl3F

The ArF (193.3 nm) irradiation of CCl4 and CCl3F has been investigated. The laser photolysis of CCl4 yields emission from CCl (A 2Δ–X 2Π), CCl2(1B1–X 1A1), Cl2[A 3Π (0u+)–X 1Σg+], and other systems. A dye laser was used to obtain the fluorescence excitation spectrum of the CCl radical near the 0–0 band center (A 2Δ–X 2Π). The CCl (A 2Δ) radicals are formed by at least a three photon absorption process and laser fluence dependences are reported for various photofragments. The ArF laser photolysis of CCl3F yields results very similar to those of CCl4. Possible mechanistic channels are presented for both CCl4 and CCl3F photolysis which are consistent with the observed photofragments, laser fluence dependences, and known thermochemical data.

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.

UV laser photochemistry of CF2Cl2

Abstract The focused ArF laser irradiation of CF 2 Cl 2 at room temperature has been investigated and emission from the CF(A 2 Σ + -X 2 Π), CF(B 2 Δ-X 2 Π), and CF 2 ( 1 B 1 -X 1 A 1 ) systems has been found. Also, under conditions of a high pressure of Ar diluent, C( 1 P 1 - 1 S 0 ) emission has been noted.

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.

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.