BROMINE ATOM-ABSTRACTION REACTIONS AT ELEVATED-TEMPERATURES BY GROUND-STATE ATOMIC RUBIDIUM, RB(5(2)S(1 2)), INVESTIGATED BY TIME-RESOLVED LASER-INDUCED FLUORESCENCE (RB(5(2)P(3/2)-5(2)S(1/2)) LAMBDA = 780 NM)/

The collisional behaviour of atomic rubidium in its 5s(S-2(1/2)) elect ronic ground state with a series of alkyl bromides has been investigat ed at elevated temperatures by time-resolved laser-induced fluorescenc e (LIF). Rb(5(2)S(1/2),,) was generated by the pulsed irradiation of r ubidium halide vapours and monitored by time-resolved laser induced fl uorescence (LIF) using the D-line transition at lambda = 780 nm (Rb(5( 2)P(3/2)-5(2)S(1/2))) excited with a pulsed Nd-YAG pumped dye-laser co upled with boxcar integration of the fluorescence signal. LIF decay pr ofiles for Rb(5(2)S(1/2)) were recorded at different total pressures w ith mixtures of an added alkyl bromide (RBr) of fixed relative composi tionf= [ RBr]/([RBr] + [He]) with excess He bath gas, from which absol ute rate data were found, essentially for single temperatures. The fol lowing absolute second-order rate constants k(R), (cm(3) molecule(-1) s(-1)) are reported for the removal of Rb(5(2)S(1/2)) by the series of alkyl bromides: CH3Br, (2.0+/-0.1)x10(-11) (875 K); C2H5Br, (1.4+/-0. 1)x10(-11) (875 K); C3H7Br, (1.2+/-0.1)x10(-11) (876 K); C4H9Br, ( 1.0 +/- 0.1) x 10(-11) (875 K); C5H11Br, ( 1.0 +/- 0.1) x 10(-11) (876 K) ; C6H13Br, ( 1.4 +/- 0.1) x 10(-11) (876 K). To the best of our knowle dge, with the exception of CH3Br and C2H5Br, no previous studies of th ese reactions with Rb(5(2)S(1/2)) have been reported, and we believe t he present investigation to be the first study of these processes by L IF. These rate constants 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)), principally measured by atomic resonance absorption spectroscopy and also by LIF. (C) 1997 Elsevier Science S.A.