Measurements of the rates of reactions of ground state atomic calcium, Ca[4s(2)(S-1(0))], with alkyl bromides at elevated temperature by time-resolved atomic resonance absorption spectroscopy [Ca(4 P-1(1)-4 S-1(0)); lambda=422.7 nm]

We present a kinetic study of reactions of ground state atomic calcium, Ca[ 4s(2)(S-1(0))], with alkyl bromides at elevated temperature by time-resolve d atomic resonance absorption spectroscopy. Atomic calcium in its electroni c ground state was generated by the broad band pulsed photodissociation of CaI2 vapour in the presence of various reactants and excess helium buffer g as and monitored in absorption at lambda = 422.673 nm {Ca[4p(P-1(1))] <-- C a[4s(2)(S-1(0))]}, Atomic decay profiles were recorded digitally in the 'si ngle-shot mode' in the time-domain using resonance radiation from a highly intense microwave-powered sealed atomic emission source and subject to comp uter analysis. Absolute second-order rate data at elevated temperature are reported for reactions of ground state calcium atoms with the following Br- containing reactants at T = 873 K: k(R)/cm(3) molecule(-1) s(-1) CH3Br (4.4 +/-0.3) (.) 10(-12), C2H5Br (1.4 +/-0.1) (.) 10(-12), C3H7Br (1.2 +/-0.1) (.) 10(-12), C4H9Br (8.5 +/-0.6) (.) 10(-13), C5H11Br (9.4 +/-0.7) (.) 10(- 13), C6H13Br (5.9 +/-0.5) (.) 10(-13), C7H15Br (6.6 +/-1.0) (.) 10(-13), CH 2Br2 (3.1 +/-0.2) (.) 10(-12) and 1,2-C2H4Br2 (1.0 +/-0.1 (.) 10(-12)). The se data, representing a totally new body of absolute rate measurements for the calcium atom, exhibiting small steric effects, are compared with analog ous rate data for reactions of atomic calcium with other halides determined hitherto by variants of time-resolved atomic resonance absorption spectros copy following pulsed irradiation at elevated temperatures in the 'single-s hot mode'.