Showing papers by "Michael E. Jenkin published in 1991"
TL;DR: The individual involvement of 69 hydrocarbons in photochemical ozone and PAN formation in Europe is examined using the Harwell photochemical trajectory model in this paper, where a detailed chemical scheme has been built up involving 384 chemical species and 684 chemical reactions to describe formation of ozone and other photochemically generated secondary pollutants.
208 citations
TL;DR: In this article, the UV-visible absorption spectrum of methylglyoxal was measured by conventional UV spectroscopic techniques (220-490 nm) and in separate experiments in which gas phase methylglyoxide was produced is situ by the chlorine-atom-initiated oxidation of acetol (390-470 nm).
Abstract: The UV-visible absorption spectrum of methylglyoxal was measured by conventional UV spectroscopic techniques (220–490 nm) and in separate experiments in which gas phase methylglyoxal was produced is situ by the chlorine-atom-initiated oxidation of acetol (390–470 nm). In the region where the two sets of results overlap, reasonably good agreement is observed. These results indicate considerably high cross-sections than those previously reported in the literature.
55 citations
TL;DR: The molecular modulation technique coupled with UV absorption spectroscopy has been used to investigate the UV spectra and kinetics of reactions of the methylperoxy radical (CH{sub 3}O{sub 2}) and the 2-hydroxyethylperoxy radicals (HOCH-sub 2}CH{superoxyethyl peroxy radical) generated by the 254-nm photolysis of the organic iodides as mentioned in this paper.
Abstract: The molecular modulation technique coupled with UV absorption spectroscopy has been used to investigate the UV spectra and kinetics of reactions of the methylperoxy radical (CH{sub 3}O{sub 2}) and the 2-hydroxyethylperoxy radical (HOCH{sub 2}CH{sub 2}O{sub 2}), generated by the 254-nm photolysis of the organic iodides CH{sub 3}I and HOCH{sub 2}CH{sub 2}I: RI + h{nu}({lambda}=254 nm) {yields} R + I and R + O{sub 2} + M {yields} RO{sub 2} + M These are believed to be CH{sub 3}OOI and HOCH{sub 2}CH{sub 2}OOI formed as intermediates in the RO{sub 2}-chaperoned recombination of iodine atoms Both CH{sub 3}O{sub 2} and HOCH{sub 2}CH{sub 2}O{sub 2} were found to obey second-order kinetic behavior owing to removal by a series of reactions initiated by the self-reactions: CH{sub 3}O{sub 2} + CH{sub 3}O{sub 2} {yields} products and HOCH{sub 2}CH{sub 2}O{sub 2} + HOCH{sub 2}CH{sub 2}O{sub 2} {yields} products Additional measurements made over the temperature range 268-350 K indicated that this parameter displays a weak negative temperature dependence E/R was found to have a value of {minus}220 {plus minus} 72 K at 760 Torr, and a value of {minus}92 {plus minus} 53 K at 108 Torr The parameter k{sub 10obs}/{sigma} had a value of (68 {plus minus}more » 04) {times} 10{sup 5} cm s{sup {minus}1} at 230 nm (p = 760 Torr, T = 298 K) Assuming the photolysis of HOCH{sub 2}CH{sub 2}I leads exclusively to the production of HOCH{sub 2}CH{sub 2}O{sub 2}, the following values of {sigma}(230 nm) and k{sub 10obs} were concluded: {sigma}(230nm)= (235 {plus minus} 025) {times} 10{sup {minus}18} cm{sup 2} molecule{sup {minus}1} and k{sub 10obs} = (160 {plus minus} 017) {times} 10{sup {minus}12} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}« less
37 citations
TL;DR: In this paper, the rate coefficient for the reaction IO + HO2 → HOI + O2 was measured at 760 Torr and 289 K. The value obtained was k5= (6.4 ± 0.7) × 10−11 cm3 molecule−1 s−1.
34 citations
TL;DR: In this paper, the authors used a laser flash photolysis of H2O2 at 248 nm in the presence of C2H4 and O2 to determine the UV spectrum of HOCH2CH2O 2 radical.
Abstract: The UV absorption spectrum of the HOCH2CH2O2 radical has been determined by the laser flash photolysis of H2O2 at 248 nm in the presence of C2H4 and O2. The absorption cross-sections were determined relative to the known cross-section of C2H5O2 at 250 nm and are in good agreement with results of a molecular modulation study in which mixtures of H2O2, C2H4 and O2 were photolysed at 254 nm. The spectrum is similar in shape and magnitude to that of C2H5O2 with a peak cross-section of 5.1 × 10–18 cm2 molecule–1 occurring at ca. 245 nm. The cross-sections determined in these studies are a factor of two higher than determined previously in this laboratory by the modulated photolysis of 2-iodoethanol, although the shape of the spectra are similar. A plausible explanation has been proposed for the low cross-sections determined in the previous study. It is concluded that the 254 nm photolysis of 2-iodoethanol produces HOCH2CH2O2 with ca. 50% yield.The removal of HOCH2CH2O2 followed second-order kinetics with an observed rate coefficient, kobs=(3.0 ± 0.5)× 10–12 cm3 molecule–1 s–1 at 296 K and 740 Torr (N2), the error referring to precision only at the 95% confidence level. The ratio kobs/σ250 was calculated to be (6.6 ± 1.1)× 105 cm s–1 in very good agreement with values determined by the molecular modulation method in this study using H2O2[(6.8 ± 0.6)× 105 cm s–1] and in the previous study using 2-iodoethanol [(6.5 ± 0.4)× 105 cm s–1] as the radical sources. The decay of HOCH2CH2O2 is attributed to a sequence of reactions initiated by the self-reaction. HOCH2CH2O2+ HOCH2CH2O2→ products (6) A reinterpretation of the previous results, accounting for the 50% yield of HOCH2CH2O2, leads to a revised value of α= 0.36 ± 0.07 for the branching ratio of the alkoxy radical product channel, 2HOCH2CH2O + O2(6a). A value of k6=(2.2 ± 0.5)× 10–12 cm3 molecule–1 s–1(95% confidence level) is concluded based on this value of α and the above value of kobs.The 193 nm photolysis of 2-chloroethanol in the presence of O2 yields HOCH2CH2O2 and HO2 simultaneously and allowed the determination of the rate coefficient for reaction (7), k7=(1.2 ± 0.3)× 10–11 cm3 molecule–1 s–1. HOCH2CH2O2+ HO2→ products (7)
28 citations
TL;DR: In this paper, the molecular modulation technique coupled with UV spectroscopy was used to monitor the behavior of HO 2 radicals produced by near-UV-modulated photolysis of Cl 2 in the presence of H 2 and O 2.
Abstract: The molecular modulation technique, coupled with UV spectroscopy, was used to monitor the behaviour of HO 2 radicals produced by the near-UV-modulated photolysis of Cl 2 in the presence of H 2 and O 2 . Experiments were carried out at both the Max-Planck-Institut (Mainz) and AEA Technology (Harwell), allowing two separate determinations of the HO 2 UV absorption spectrum. These are in excellent agreement throughout the wavelength range 200–260 nm, with σ 220 (HO 2 ) = 3.4 × 10 −18 cm 2 molecule −1 . A comparison with previous measurements is made. Removal of HO 2 in the chemical system used in the present experiments occurs by self-reaction (eqn. (4)). The value of k 4 at 298 K and 760 Torr was found to be (2.44 ± 0.20) × 10 −12 cm 3 molecule −1 s −1 with O 2 as the bath gas, and (2.84 ± 0.30) × 10 −12 cm 3 molecule −1 s −1 with a bath gas of predominantly N 2 .
22 citations
2 citations