Kinetic investigation of chlorine atom-abstraction reactions by ground-state atomic rubidium, Rb(52S1/2), by time-resolved laser-induced fluorescence [Rb(52P3/2-52S1/2); λ=780 nm] following pulsed irradiation

We present a kinetic study of the collisional behaviour of atomic rubidium in its 5s(S-2(1/2)) electronic ground state with a series of alkyl chlorides at elevated temperatures by time-resolved laser-induced fluorescence (LIF). Rb(5(2)S(1/2)) atoms were generated by the pulsed irradiation of rubidium halide vapours at elevated temperatures in the presence of low concentrations of alkyl chlorides and excess helium buffer gas. The concentration of the metal atom was then monitored via the D-line transition at lambda = 780 nm [Rb(5(2)P(3/2)-5(2)S(1/2))] using a pulsed Nd-YAG pumped dye-laser with boxcar integration of the fluorescence signal. LIF decay profiles for Rb(S'S,,) were investigated at different total pressures with mixtures of an added alkyl chloride (RCl) of fixed relative composition f = [RCI]/([RCI] + [He]) with excess He bath gas from which absolute rate data were found, essentially for single temperatures for a series of alkyl chlorides. Decay profiles were also investigated in excess helium alone at Various temperatures in order to correct for diffusional loss for the atomic decays. The diffusion of Rb(5(2)S(1/2)) in krypton gas is also described. The following absolute second-order rate constants k(R) (cm(3) molecules(-1) s(-1)) are reported for the removal of Rb(5(2)S(1/2)) by the series of alkyl chlorides: CH3Cl, (7.8 +/- 0.3) X 10(-12) (908K); C2H5Cl, (1.5 +/- 0.1) X 10(-11) (906K); C3H7Cl, (7.1 +/- 0.1) X 10(-12) (842K); C4H9Cl, (10.0 +/- 0.3) X 10(-12) (896K); C5H11Cl, (6.6 +/- 0.1) X 10(-12) (866 K); C6H13Cl, (7.74 +/- 0.3) X 10(-12) (843 K); C7H15Cl, (7.9 X 0.1) X 10(-12) (851 K). Whilst the collisional behaviour of Rb(5(2)S(1/2)) with some reactants has been investigated by direct monitoring in the time-domain using various methods, to the best of our knowledge, with the exception of CH3Cl, no previous studies of these reactions have been reported, and we believe the present investigation constitutes the first study of these processes in the presence of the alkyl chlorides by LIE These rate constants, which represent a new body of rate data for Rb(5(2)S(1/2)) are compared, where possible, with analogous data for K(4(2)S(1/2)), Na(3(2)S(1/2)) and Cs(6(2)S(1/2)) which were variously measured by atomic resonance absorption spectroscopy and LIF.