A.E. Croce

Kinetics of the recombination reaction between F atoms and FCO radicals

Abstract The laser flash photolysis-absorption technique has been used to study the F + FCO + M → CF 2 O + M recombination reaction between 20 and 700 Torr of M = CF 4 at 296 K. The values k rec,0 = (5.6 ± 1.2) × 10 −29 [CF 4 ] cm 3 molecule −1 s −1 and k rec,∞ = (7.9 ± 1.1) × 10 −11 cm 3 molecule −1 s −1 were determined by extrapolation of the fall-off curve. An analysis of k rec,0 with respect to energy-transfer properties has been carried out. The measured k rec,∞ value is in reasonable agreement with the predictions of the simplified statistical adiabatic channel model. For the FCO + FCO → CF 2 O + CO reaction a rate coefficient of (2.0 ± 0.2) × 10 −11 cm 3 molecule −1 s −1 was determined.

Pulsed laser photolysis study of the reaction Cl+FSO3+M→FSO2OCl+M

Abstract The recombination reaction Cl+FSO3+M→FSO2OCl+M has been studied by ArF excimer laser photolysis-visible absorption spectroscopy in the pressure range 24–708 Torr of the bath gases He and CF4 at 297 K. For M = CF4 the limiting high-pressure rate constant is (6.0±0.7) × 10−11 cm3 molecule−1 s−1. Small fall-off effects are apparent for He diluent. An analysis of the in terms of the statistical adiabatic channel model leads to α/β=0.52 for the ratio of the looseness and Morse parameters. For Cl+FSO2OCl→Cl2+FSO3 a rate constant of (1.3±0.2) × 10−11 cm3 molecule−1 s−1 was determined.

Spectrokinetic determination of fluorosulphate radical absorption cross-sections

Abstract The absorption cross-sections of fluorosulphate radicals (FSO 3 ) were measured in the wavelength range 340 – 450 nm at 295 K using a technique of combined ArF excimer laser flash photolysis and absorption spectroscopy. The absorption cross-sections of fluorine fluorosulphonate (FSO 2 OF) between 193 and 360 nm are also reported.

Kinetics of formation and unimolecular decomposition of the FS(O2)OOO radical

Abstract The kinetics and mechanism of the 193 nm laser flash photolysis of FSO 2 OF in the presence of O 2 and the bath gases N 2 and CF 4 were studied at 295 and 383 K. FSO 3 radicals and F atoms are formed in the primary photolytic process. Subsequently, the FO 2 radicals, produced by the combination of F with O 2 , react with FSO 3 leading to the intermediate trioxide FS(O 2 )OOOF. To explain the build-up of the roomtemperature, time-resolved absorption signals observed at 450 nm, the formation of the novel FS(O 2 )OOO radical, via F atom abstraction from the trioxide by FO 2 , is proposed. FS(O 2 )OOO then dissociates unimolecularly on a millisecond timescale into FSO 3 and O 2 . This radical is not formed by recombination of FSO 3 with O 2 . At 383 K, the faster thermal decomposition of FO 2 radicals precludes the formation of FS(O 2 )OOO.

Experimental and theoretical study of the recombination reaction of FC(O)O radicals

Abstract The kinetics of the recombination reaction of FC(O)O radicals has been experimentally and theoretically investigated. The FC(O)O radicals were generated by excimer laser flash photolysis of mixtures of (FCO) 2 and O 2 in excess of CO at 297 K and monitored by absorption spectroscopy at 545 nm. In agreement with the predictions from unimolecular rate theory, no appreciable falloff effects were observed for total pressures ranging from 117 to 727 Torr. The measured limiting high pressure rate coefficient, k rec, ∞ = (7.0 ± 1.1) × 10 −13 cm 3 molecule −1 s −1 , agrees very well with that predicted by a simplified version of the statistical adiabatic channel model. The influence of the dominant potential energy surface features on k rec, ∞ was examined between 200 and 600 K.

Absorption cosfficients for the fluorosulphate radical

Abstract The absorption coefficients of ground state FSO 3 radicals have been measured in the wavelength range 340–470 nm at 295 K. The radicals are formed after fast collisional deactivation of the excited FSO 3 radicals initially generated in the photodissociation at 193 nm of F 2 S 2 O 6 in He. The absorption coefficients increase monotonically from 7.21×10 1 to 1.16×10 3 M −1 cm − over the spectral range investigated. The present results are in good agreement with previous determinations from this laboratory.

Kinetics of the reaction of Cl atoms with FC(O)O and FC(O) OCl

Abstract The kinetics of the Cl + FC(O) O + M → FC(O)OCl + M recombination reaction has been studied by using an ArF excimer laser flash photolysis technique over the 3–650 mbar pressure range of the bath gases He and SF 6 at 295 K. The reaction was found to be close to the second-order regime at total pressures greater than about 100 mbar. The derived limiting high-pressure rate coefficient is (3.1 ± 0.3) × 10 −11 cm 3 molecule −1 s −1 . For the Cl + FC(O)OCl → FC(O)O + Cl 2 reaction a rate coefficient of (1.5 ± 0.2) × 10 −11 cm 3 molecule −1 s −1 was determined. An analysis of the results in terms of the simplified versions of the statistical adiabatic channel model has carried out.

Collisional quenching of excited FSO3 radicals produced by laser photodissociation of F2S2O6 at 193 nm

Abstract Collisional deactivation of excited FSO 3 radicals generated by 193 nm excimer laser photodissociation of F 2 S 2 O 6 was studied by examining absorption decay times at 450 nm for the He, N 2 , O 2 and F 2 S 2 O 6 collision partners. Double exponential decays were observed which were attributed to FSO 3 radicals in different states of excitation. The following quenching rate constants for the short-lived species were measured for the He and N 2 quenchers at 295 K: (5.8 ± 0.8) × 10 −15 and (9.7 ± 1.4) × 10 −15 cm 3 molecule −1 s −1 respectively. For the long-lived species the values (1.5 ± 0.2) × 10 −15 , (3.2 ± 0.3) × 10 −15 , (2.6 ± 0.4) × 10 −14 and (1.6 ± 0.2) × 10 −13 cm 3 molecule −1 s −1 were determined for He, N 2 , O 2 and F 2 S 2 O 6 respectively. Arguments are presented which suggest that the present quenching data correspond to the vibrational relaxation of highly excited FSO 3 radicals.

Quenching of FSO3(B̃2E) generated by 193 nm photodissociation of FSO2OF and F2S2O6

Abstract The collisional relaxation of electronically excited FSO3 radicals, generated by laser photodissociation of FSO2OF and F2S2O6 at 193 nm, was studied by examination of the absorption rise profiles due to the appearance of ground state vibrationally excited FSO3 radicals. Room temperature quenching rate constants for collision partners He, N2, O2, Cl2, CO2, CF4, FSO2OF and F2S2O6 were measured (in units of 109 dm3 mol−1 s−1); they are 2.0 ± 0.2, 1.4 ± 0.2, 1.6 ± 0.2, 3.6 ± 0.4, 3.2 ± 0.4, 2.7 ± 0.4, 11 ± 1 and 20 ± 2 respectively. Both precursors employed yield electronically excited radicals with essentially the same kinetic properties and a radiative lifetime (4.2 ± 0.5 μs) which agrees very well with that evaluated from the integrated oscillator strength for the B2E state of the FSO3 radical. The experimental quenching cross-sections are well correlated with the well depth of the FSO3(B2E)-quencher interaction.

The photochemical reaction between chlorine and chlorine perchlorate at 366 nm

Abstract The photolysis of Cl 2 in the presence of Cl 2 O 4 at 366 nm in the gaseous phase has been investigated at 303 K. The UV absorbance of the gas mixture has been recorded spectrophotometrically after each photolysis interval to monitor the reactant Cl 2 O 4 pressure and determine quantitatively the chlorinated reaction products. A quantum yield for Cl 2 O 4 consumption of 2.0±0.2 has been determined. The main reaction products are Cl 2 O 7 , Cl 2 and O 2 , accompanied by small quantities of Cl 2 O 6 and OClO. A mechanism involving ClO 4 radicals formed in the Cl atom abstraction from Cl 2 O 4 by Cl is proposed.