RATE COEFFICIENTS FOR QUENCHING OF CL(P-2(1/2)) BY VARIOUS ATMOSPHERIC GASES

Rate coefficients for quenching of the upper spin-orbit state of chlorine Cl(P-2(1/2)) by a variety of collision partners have been measured at room temperature. The method used was laser flash photolysis of NOCl or ClONO2 with resonance fluorescence detection of chlorine atoms using a strongly reversed resonance lamp for preferential detection of Cl(P-2(1/2)) The rate coefficients were (units of cm(3) motecule(-1) s(-1)):CF4, (2.3 +/- 0.3) x 10(-11); CF2Cl2, (3.3 +/- 0.5) x 10(-10) CH4, (2.2 +/- 0.3) x 10(-11); ClONO2, (1.7 +/- 0.3) x 10(-10); O-2, (3.5 +/- 0.5) x 10(-13); N-2, (5.0 +/- 1.5) x 10(-15); He, (6.0 +/- 1.0) x 10-(14); Ar, (3.0 +/- 1.0) x 10(-16). These values are in good overall agreement with recent determinations which used IR laser detection of Cl(P-2(1/2)). Quenching by helium was found to be unusually fast, explaining in part discrepancies with earlier studies which used resonance absorption detection. The reaction with CH4 was shown to proceed exclusively by quenching, and not to involve enhanced reactivity of Cl(P-2(1/2)) relative to the ground-state species. Additionally, the yield of Cl(P-2(1/2)) 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 Cl(P-1(3/2)) with NOCl was measured to be (9.6 +/- 1.5) x 10(-11) cm(3) molecule(-1) s(-1).