Reactions of ground state atomic calcium, Ca[4s 2( [formula omitted])], investigated by time-resolved atomic resonance absorption spectroscopy at elevated temperature

Abstract

Absolute second-order rate data at elevated temperature are reported for reactions of ground state calcium atoms, Ca[4s 2( 1 S 0 )], generated by broad band pulsed photodissociation of CaI 2 vapour in the presence of various reactants and excess helium buffer gas and monitored by time-resolved atomic resonance absorption spectroscopy at λ=422.673 nm ( Ca[4 p( 1 P 1)]← Ca[4 s 2( 1 S 0)] ). Unlike most previous time-resolved atomic resonance absorption measurements on ground state atomic calcium at this wavelength, complete decay profiles were recorded digitally in the ‘single-shot mode’ in the time-domain using resonance radiation from a highly intense microwave-powered sealed atomic emission source. The following second-order rate constants for the reactions of Ca( 1 S ) are reported: k R (cm 3 s −1 per molecule) (873 K), 1-C 3H 7Cl (3.5±0.1)×10 −12; 1-C 4H 9Cl (2.5±0.2)×10 −12; 1-C 5H 11Cl (2.2±0.4)×10 −12; 1-C 6H 13Cl (2.8±0.3)×10 −12; CHF 2Cl (4.8±0.2)×10 −12; and CH 3I (16.3±3.0)×10 −12 (errors 1 σ). These data are compared with analogous rate data for reactions of atomic calcium with other halides. Estimates are also reported for diffusion coefficients for Ca( 1 S 0 ) in various buffer gases, D 12 (cm 2 s −1) (STP): He, 0.47±0.05; Kr, 0.14±0.02; Xe, 0.09±0.02; and N 2, 0.26±0.02. These are found to be in sensible accord with analogous values of D 12 ( Ba( 1 S 0)+ He , Kr and Xe) derived hitherto by laser methods.