Rate coefficients for quenching of the upper spin-orbit state of chlorine C1(2Pl12) by a variety of collision partners have been measured at room temperature. The method used was laser flash photolysis of NOCl or CIONO, with resonance fluorescence detection of chlorine atoms using a strongly reversed resonance lamp for preferential detection of C1(2Pl12). The rate coefficients were (units of cm3 molecule-' s-'): CF, , (2.3 & 0.3) x lo-'' ; CF,C12 , (3.3 & 0.5) x lo-''; CH, , (2.2 & 0.3) x lo-'' ; CIONO, , (1.7 It 0.3) x lo-''; 0 2 , (3.5 & 0.5) x N, , (5.0 & 1.5) x He, (6.0 & 1.0) x lo-',; Ar, (3.0 & 1.0) x lo-'". These values are in good overall agreementwith recent determinations which used IR laser detection of C1(2Pl12). Quenching by helium was found to be unusually fast, explaining in part discrepancies with earlier studies which used resonance absorption detection.The reaction with CH, was shown to proceed exclusively by quenching, and not to involve enhanced reactivity of C1(2Pl12) relative to the ground-state species. Additionally, the yield of C1(2Pl12) from the photolysis of chlorine nitrate was found to be 30% of the overall chlorine atom yield at 308 nm. The rate coefficient for the reaction of C1(2P312) with NOCl was measured to be (9.6 & 1.5) x lo-'' cm3 molecule-' s -I .
The rate coefficient for the reaction OH + ClO f products (1) was measured under pseudo-first-order conditions in OH. A discharge flow system was used to produce ClO, and its concentration was measured by UV/visible absorption. OH was produced by pulsed laser photolysis of O 3 (or ClO) at 248 nm in the presence of H 2 O and was monitored by laser-induced fluorescence. The value of k 1 between 234 and 356 K is given by k 1 (T) ) (8.9 ( 2.7) × 10 -12 exp[(295 ( 95)/T] cm 3 molecule -1 s -1 , where uncertainties are 95% confidence limits and include estimated systematic uncertainties. Our value is compared with those from previous investigations.
Rate coefficients have been measured for the reactions of Cl atoms with methanol (k 1 ) and acetaldehyde (k 2 ) using both absolute (laser photolysis with resonance fluorescence) and relative rate methods at 295 Ϯ 2 K. The measured rate coefficients were (units of 10Based on a critical evaluation of the literature data, the following rate coefficients are recommended: k 1 ϭ (5.4 Ϯ 0.9) ϫ 10 Ϫ11 and k 2 ϭ (7.8 Ϯ 1.3) ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 (95% confidence limits). The results significantly improve the confidence in the database for reactions of Cl atoms with these oxygenated organics. Rate coefficients were also measured for the reactions of Cl 2 with CH 2 OH, k 5 ϭ (2.9 Ϯ 0.6) ϫ 10 Ϫ11 and CH 3 CO, k 6 ϭ (4.3 Ϯ 1.5) ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 , by observing the regeneration of Cl atoms in the absence of O 2 . Based on these results and those from a previous relative rate study, the rate coefficient for CH 3 CO ϩ O 2 at the high pressure limit is estimated to be (5.7 Ϯ 1.9) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s
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