Reactions of ground state atomic calcium, Ca[4s2()], investigated by time-resolved atomic resonance absorption spectroscopy at elevated temperature

Autor: David Husain, J. W. Adams, Junfeng Geng
Rok vydání: 2001
Předmět:
Zdroj: Journal of Photochemistry and Photobiology A: Chemistry. 141:93-99
ISSN: 1010-6030
DOI: 10.1016/s1010-6030(01)00449-x
Popis: 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 3 H 7 Cl (3.5±0.1)×10 −12 ; 1-C 4 H 9 Cl (2.5±0.2)×10 −12 ; 1-C 5 H 11 Cl (2.2±0.4)×10 −12 ; 1-C 6 H 13 Cl (2.8±0.3)×10 −12 ; CHF 2 Cl (4.8±0.2)×10 −12 ; and CH 3 I (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.
Databáze: OpenAIRE
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