Electronically excited iodine atoms, I(5 p52P [formula omitted]): a kinetic study of some chemical reactions by atomic absorption spectroscopy using time-resolved attenuation of resonance radiation at λ = 206.23 nm {I[5 p46 s( 2P [formula omitted]) ← 5 p5( 2P 0[formula omitted])

Abstract

Electronically excited iodine atoms, I(5 p 5 2P 1 2 ), 0.943 eV above the lower spin orbit level (J = 3 2 ) of the 5 p 5 ground state configuration, have been generated by the ultra-violet pulsed irradiation of CF 3I in the presence of excess helium buffer gas. The optically metastable atoms were monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation at λ = 206.23 nm {I[5 p 46 s ( 2P 3 2 ) ← 5 p 5( 2P 0 1 2 )]}. The kinetic decay of the excited atoms in the presence of the added gases Cl 2, Br 2, ICl, IBr, NOCl and NOBr has been investigated in detail and second order rate constants for chemical reaction with these molecules are reported and compared with rate data obtained hitherto from plate photometry. Further, the temperature dependence of the reaction rate constants has been studied in the range 294–421 K, the results for the chemical reactions of I(5 2P 1 2 ) with Cl 2 and Br 2 being most detailed. The Arrhenius parameters for these two reactions were found to be as follows: ▪