Quenching kinetics of I(2P½) by cyanides. Isotope effect in the quenching by CH3(D)CN

Abstract

The quenching of electronically excited iodine atoms I(2P½ I*) by CH3CN, CD3CN, HCN, C2H5CN, and (CN)2 was studied. Good agreement was found for I* deactivation by acetonitrile and perdeuteroacetonitrile using two widely different techniques, namely time-resolved atomic absorption (TRAA) and chemical laser threshold gain (CLTG). The kinetic isotope effect determined, kH/kD, was 2.2 ± 0.5 for both methods. This low value would support the existence of a noticeable reactive path and a possible channel assisted by a curve-crossing mechnism. Values here reported for the second-order rate constants for I* deactivation are, respectively, (1.2 ± 0.1)× 10–13, (5.3 ± 0.5)× 10–14, (3.3 ± 0.2)× 10–14, (1.3 ± 0.1)× 10–13, (2.2 ± 0.2)× 10–15 cm3 molecule–1 s–1 for CH3CN, CD3CN, HCN, C2H5CN and (CN)2, according to the TRAA method. Results from CLTG measurements are (1.6 ± 0.1)× 10–13, (7.3 ± 0.2)× 10–14 and (8.3 ± 0.1)× 10–14 cm3 molecule–1 s–1 for CH3CN, CD3CN and HCN, respectively.