Dynamics of ionization processes of the ethylene–HF complex: a direct ab-initio dynamics study

Abstract

Ionization processes of the ethylene–HF (C2H4–HF) complex have been studied by means of both ab-initio molecular orbital and direct ab-initio dynamics methods. The ab-initio calculations of C2H4–HF show that the H-end of HF orients toward the center-of-mass of C2H4 by the dipole interaction (i.e. the H-orientation form). For the ionized state of C2H4–HF, it was found that the cation complex [C2H4–FH]+ with a planer structure is formed as the most stable form. The potential energy curve (PEC) calculated as a function of C2H4–HF center-of-mass distance (Rcm) indicates that the HF molecule is weakly bound on C2H4 at the neutral state, whereas the PEC for the cation system constrained to the H-orientation form is entirely repulsive. On the other hand, the PEC constrained to the F-orientation form is strongly bound. Also, it was found that the complex on PES at the ground state has a wide Franck–Condon region for the ionization. The direct ab-initio dynamics calculations (HF/6-311G(d,p) level) have been carried out for the ionization dynamics of C2H4–HF. The calculations showed that two reaction channels were obtained as products: one is a complex formation channel in which the complex composed of C2H4+–FH was formed, and the other one is a dissociation channel in which the trajectory leads to directly the dissociation product C2H4++HF without complex formation. The mechanism, in particular the preference for the reaction channels, is discussed on the basis of the theoretical results.