Photodissociation dynamics of jet-cooled ClNO on S1(1 1A″): An experimental study

Abstract

We report measurements of photofragment yield (PHOFRY) spectra and NO E, V, R distributions following dissociation of jet-cooled ClNO on the S1(1 1A″) electronic surface. The dissociative S1(1 1A″)←S0(1 1A′) transition shows diffuse vibrational structure with a progression in ν1, the NO stretch. The absorption and PHOFRY spectra consist of two bands, corresponding to excitations into S1(000) and S1(100), whose widths are 1300±100 and 1000±70 cm−1, respectively. The relative partial absorption cross sections are S1(000):S1(100)=2.3:1.0. The narrowing of the absorption bands with increasing ν1 quanta is a consequence of the mismatch between ν1 and the free NO vibrational frequency. Dissociations on S1(000) and S1(100) yield NO in v″=0 and 1, respectively. The NO(X2∏) rotational distributions in v″=0 and 1 are inverted, peaking at J″∼30.5 with widths of 10±1 J″, and they do not vary significantly when the photolysis laser is scanned across the absorption band. The evolution of NO vibrational and rotational excitations appear to be largely uncoupled. In NO v″=0 and 1, the upper spin–orbit state 2∏3/2 is more populated than the lower state 2∏1/2. For both v″=0 and 1, the Λ-doublet ∏(A″) component of NO(2∏1/2) is more populated than the ∏(A′) component by a ratio of ∼3:1, as expected for excitation to a π* orbital of a″ symmetry, but this propensity is much lower for NO(2∏3/2), possibly due to perturbations with another surface. The absorption spectra and NO V, R distributions are in good agreement with recent dynamical calculations on a three-dimensional (3-D) potential-energy surface (PES) calculated ab initio. The vibrational distribution appears to be determined near the Franck–Condon (FC) region, while final-state interactions affect the rotational distributions at larger Cl–NO separations.