The reaction of chlorine atoms, Cl(3 2p J), with nitric acid in the gas phase

Abstract

A kinetic investigation is presented of the reaction between ground state chlorine atoms Cl(3 2P J ), with a Boltzmann equilibrium in the J = 3 2 and J = 1 2 ( E = 881 cm −1) spin—orbit levels, and nitric acid vapour. Atomic chlorine was generated by the repetitive pulsed irradiation of molecular chlorine in the visible region of the spectrum in a flow system kinetically equivalent to a static system and monitored by time-resolved resonance absorption in the vacuum UV at λ = 138.79 nm (CL((3p) 4(4s), 2P 5 2 ) ← Cl((3p) 5, 2P 3 2 )). The absolute second-order rate constant for the reaction with methane, used here as kinetic standard, yielded k(Cl + CH 4) = (1.03 ± 0.22) × 10 −13 cm 3 molecule −1 s −1 (room temperature; error, 2σ) which is in good agreement with previous measurements of this quantity obtained by a variety of methods. The reaction rate constant with nitric acid was found to be k(Cl + HNO 3) = (3.4 ± 1.6) × 10 −14 cm 3 molecule −1 s −1 (room temperature; error, 2σ). This is compared with previous rate data derived from flow discharge with mass spectrometric measurements.