Kinetic and Mechanistic study of the Reactions of O( 1 D 2 ) with HCN and CH 3 CN

A laser flash photolysis–resonance fluorescence (LFP‐RF) technique is employed to investigate the kinetics and mechanism of the reactions of O( 1 D 2 ) with HCN [reaction (1)] and CH 3 CN [reaction (2)] as a function of temperature over the range 193–430 K. The experiments involve time‐resolved RF detection of O( 3 P J ) or H( 2 S 1/2 ) following LFP of O 3 /X/He mixtures (X=HCN or CH 3 CN), some of which also contain N 2 , H 2 , and/or NO 2 . Measured rate coefficients for total removal of O( 1 D 2 ) by HCN and CH 3 CN are well‐described by the following Arrhenius expressions (units are 10 −10 cm 3  molecule −1  s −1 ): k 1 ( T )=1.08exp(+105/ T ) and k 2 ( T )=2.54exp(−24/ T ). Temperature‐dependent product yields of O( 3 P J ), k 1a / k 1 and k 2a / k 2 are well‐described by the following Arrhenius‐type expressions: k 1a / k 1 =0.150exp(+200/ T ) and k 2a / k 2 =0.0269 exp(+137/ T ). The H( 2 S 1/2 ) yield from reaction (2) is found to be 0.16±0.03 independent of temperature (200–423 K). Large 298 K yields of H( 2 S 1/2 ), 0.68±0.12 produced per O( 1 D 2 ) destroyed by HCN, are observed for reaction (1). However, observed kinetics suggest that only about half of detected H( 2 S 1/2 ) is generated as a primary product of the O( 1 D 2 )+HCN reaction, with the remainder generated via a fast secondary reaction. The implications of the reported kinetic and mechanistic results for understanding the atmospheric chemistry of HCN and CH 3 CN are discussed.