Predissociation in the Ã′ A″ State of HNO

Abstract

The ùA″ – X¹ A’ band system of HNO (υ_oo=13154 cm⁻¹) has been studied at high resolution in absorption using the technique of flash photolysis [1–3], and at lower resolution in emission from chemiluminescent reactions [4,5]. Clement and Ramsay [4] observed breaking-off in emission in the coarse rotational structure of two vibronic levels of HNO and one vibronic level of DNO, and hence deduced an upper limit of ~17000 cm^−l (203 kJ mol⁻¹) for the energy of dissociation of HNO to H + NO. Broadening of the absorption line widths was also observed in the 101-000 vibronic band, with origin at 16970 cm⁻¹ [2]. Freedman extended these line width measurements [3], and concluded that the predissociation probably involves a two-step mechanism involving intermediate levels either of the ground state or of the postulated ã ³A” state. Numerous small rotational perturbations are also evident throughout the Ã−X band system, and may involve the same intermediate state. From observations of 0₂(¹ Δg) sensitization of HNO chemiluminescence Ishiwata et al. [5] have concluded that the origin of the ³A” state lies in the region of 6800 cm^−l above the ground state. The aim of our work is to elucidate these perturbative and predissociative mechanisms.