The Unimolecular Loss of HF by Simple Inorganic Ions: A Computational Dynamic Reaction Path Study

Abstract

The metastable dissociations of a series of simple inorganic gaseous ions of general formula (H,F,M)+, including NF3H+ (M = NF2), N2F2H+ (M = FN2), F2NOH2+ (M = FNOH) and FNOH+ (M = NO) have been investigated using classical dynamics in order to rationalise their mass-analysed ion kinetic energy (MIKE) spectra which, from earlier experimental studies, showed the systematic loss of neutral hydrofluoric acid, HF, accompanied by a fairly large release of translational energy ( T). All the simulations were initiated in correspondence of the transition structures involved in the above decompositions and expanded on the related Hartree–Fock potential energy surfaces, calculated “on the fly” during the evolution of the trajectories according to the Dynamic Reaction Path methodology. The initial associated momenta were deduced by performing a standard kinetic analysis of the above dissociations taking into account the specific features of the MIKE experiments. For all the above ions, the resulting computed Ts are in reasonable agreement with the experimental values. In addition, from a more accurate analysis of the trajectories, it could be possible to appreciate qualitatively both the specific role of the internal degrees of freedom of the decomposing ions and the dynamic and energetic influence of the HF–M+ ion–neutral complex located between the dissociation products and the tight transition structure involved in the above decompositions.