Ab initio CI study of the photodissociation of nitrosyl chloride (CINO)

Abstract

Potential-energy curves for the ground and excited singlet states of nitrosyl chloride (CINO) in the energy region up to 8.5 eV have been calculated by means of the CIPSI method, which combines variation and perturbation techniques in order to take into account electron correlation effects. The calculated dissociation energy De for the ground state is 1.58 eV which can be compared with the experimental value of 1.55 eV. The three first A′' and two first A′ symmetry states at low energy are all repulsive along the Cl-N coordinate and are responsible for the direct dissociative processes obtained in the 6000-3000 Å energy range. At = 2000 Å a bound state has been observed which clearly indicates that the photofragmentation in NO(X)+Cl 2Po is not due to a direct dissociation but should involve a predissociative mechanism through a crossing with a triplet state or a rapid internal conversion to the hot ground state. Between 1700 and 1200 Å the electronic states are numerous and involve a large contribution of Rydberg orbitals. These states dissociate towards NO A2Σ−. C2Π and D2Σ− corroborating experimental observations.