An experimental study of the gas-phase reactions of the NO3 radical with three sesquiterpenes: isolongifolene, alloisolongifolene, and alpha-neoclovene

Isolongifolene, alloisolongifolene, and alpha-neoclovene are sesquiterpenes , hydrocarbons of general formula C15H24; these sesquiterpenes contain a si ngle carbon-carbon double bond. They are emitted to the atmosphere by plant s during the night and the day. Rate coefficients for the reactions between the night-time atmospheric oxidant, the NO3 radical, and isolongifolene (k (1)), alloisolongifolene (k(2)), and alpha-neoclovene (k(3)) have been dete rmined at T = 298 +/- 2 K and P = 760 +/- 10 Torr by the relative-rate meth od. The values of the rate constants measured were k(1) = (3.9 +/- 1.6) x 1 0(-12) cm(3) molecule(-1) s(-1), k(2) = (1.4 +/- 0.7) x 10(-12) cm(3) molec ule(-1) s(-1) and k(3) = (8.2 +/- 4.6) x 10(-12) cm(3) molecule(-1) s(-1). The reference reaction for determining k(1) and k(3) was the reaction betwe en NO3 and alpha-pinene (k(9)), and the reference reaction for determining k(2) was the reaction between NO3 and cyclohexa-1,4-diene (k(10)). The valu es used for the rate constants for the reference reactions are k(9) = 6.2 x 10(-12) cm(3) molecule(-1) s(-1) and k(10) = 6.6 x 10(-13) cm(3) molecule( -1) s(-1), with likely errors of 30% on each. Error limits quoted on our me asured rate constants (k(1)-k(3)) include these potential errors on k(9) or k(10). The chemical atmospheric lifetimes of these sesquiterpenes are cons idered. They are short, and are dominated by the reaction with the NO3 radi cal by night; OH and O-3 both make significant contributions by day.