Infrared laser enhanced reactions: Temperature resolution of the chemical dynamics of the O3† + NO reaction systen

Abstract

The rate constant for the decay of vibrationally excited ozone, O₃^†, in the O₃^† + NO reaction system has been measured from 153 to 373 K. Vibrationally excited O₃ was produced in the asymmetric stretch normal mode by absorption of square wave modulated emission from a CO₂ laser tuned to the P (30) 9.6 μm transition. Under appropriate experimental conditions, a rapid V→V coupling process involving all three normal modes of O₃ is believed to set up a Boltzmann population distribution among them. Reaction or relaxation of O₃⁺ out of this subset of normal modes is observed to proceed through a weighted average of rate constants. From the effects of temperature and buffer gas pressures an assessment can be made as to the predominant loss mechanism for the various modes. While there are three separate convolution schemes which appear to fit our data, we are persuaded to emphasize one whereby all three modes contribute via a reaction channel described by k_D = (2.0×10⁻¹¹) exp(−1525/T) cm³ molecule⁻¹⋅sec⁻¹ while ν₂ alone is active in a V→T relaxation process given by k_A = (1.0×10⁻¹³) exp(−39.2/T cm³ molecule⁻¹⋅sec⁻¹. A comparison of the Arrhenius parameters for the reaction channels of O₃^† with parameters for the corresponding processes involving thermal O₃ yields specific information about the effect of vibrational energy on the reaction dynamics.