Temperature dependences of the reactions of the nitrate radical with some alkynes and with ethylene

Abstract

The temperature dependences of the rate constants for the reactions of NO₃ with ethylene and a series of alkynes have been studied using a time-resolved flow method over the temperature range 295–523 K. In all these reactions the variations of the rate constants follow closely the Arrhenius expression, for which the parameters A and E_a, have been calculated. The activation energies were compared with literature values for the addition reactions of OH, O(³P), CH₃, CH₃O₂ and CH₃COO₂ with alkenes and alkynes as well as with those for the reactions of NO₃ with CH₃SH, CH₃SH, and CH₃SSCH₃. We conclude that the behaviour of the nitrate radical towards alkenes and alkynes resembles that of the addition of CH₃O₂ and CH₃COO₂ to alkenes. Unexpected gas-phase or wall losses of NO₃ contribute a first-order decay rate of less than 0.04 s^–1 at 523 K. We also obtained upper limits for the rate constants for the interactions of NO₃ with O₂ and SO₂ at 473 K of 1.2×10^–17 cm³ molecule^–1 s^–1.