Measurement of the Reaction Rate of BrNO + Br →Br₂ + NO by the Thermal Lens Method

Abstract

The photochemistry of nitrosyl halides has been intensively investigated by many workers; especial interest has been concentrated on the mechanisms of vibrationally excited NO production. Direct formation of vibrationally excited NO is now confirmed by the UV photolysis studies of C1NO by many investigators, including Basco and Norrish [1] and Moser et al. [2]. However, the photolysis of BrNO at visible wavelengths has not been completely established. Grimley and Houston [3] reported that vibrationally excited NO (v=2-3) was produced in the photolysis of BrNO for wavelengths greater than 480 nm. They assigned the mechanism of the formation of NO(v) as

$$Br\, + \,BrNO\, \to \,B{r_2}\, + NO\,\left( {\Delta H\, = \, - 17.4kcal/mol} \right)$$

(1)

by monitoring IR emissions in the 5.2 μm region through a cold gas filter of NO. The rate constant of this process evaluated by them was k₁ = 5.16 × 10⁻¹² [cm³molecule⁻¹s⁻¹], which was consistent with that measured by flash photolysis/mass spectrometry by Price and Ratajczak [4], but about two orders of magnitude smaller than that reported by Hippler et al. [5] who monitored Br₂ absorption.