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

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 o rients toward the center-of-mass of C2H4 by the dipole interaction (i.e. th e 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 mo st stable form. The potential energy curve (PEC) calculated as a function o f C2H4-HF center-of-mass distance (R-cm) indicates that the HF molecule is weakly bound on C2H4 at the neutral state, whereas the PEC for the cation s ystem constrained to the H-orientation form is entirely repulsive. On the o ther 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 calc ulations (HF/6-311G(d,p) level) have been carried out for the ionization dy namics of C2H4-HF. The calculations showed that two reaction channels were obtained as products: one is a complex formation channel in which the compl ex composed of C2H4+-FH was formed, and the other one is a dissociation cha nnel in which the trajectory leads to directly the dissociation product C2H 4++HF without complex formation. The mechanism, in particular the preferenc e for the reaction channels, is discussed on the basis of the theoretical r esults.