Dynamics of the ionization processes of benzene-H2O clusters:: A direct ab initio dynamics study

Ionization processes of benzene-water cluster Bz(H2O)(n) (n = 1 and 2) have been studied by means of direct ab initio dynamics calculations. The ab initio calculations for the BzH(2)O 1:1 neutral complex show that in the minimum energy structure the water hydrogens point toward the center of mass of the benzene ring (the dipole orientation form). The potential energy curve calculated as a function of the benzene-H2O center of mass distance (R-cm) indicates that the H2O molecule is weakly bound to the benzene ring. The potential energy curve for the cationic system BzH(2)O(+) constrained to the dipole orientation form is purely repulsive, whereas the curve calculated for the oxygen orientation form has a fairly deep well. The complex has a wide Franck-Condon (FC) region for the ionization. Dynamics of the ionization process of the BzH(2)O complex was studied by means of direct ab initio dynamics calculations. A total of 11 points in the FC region were chosen as initial points. The trajectories started from both the equilibrium point of BzH(2)O (R-cm 3.395 Angstrom) and the outer classical turning point in the FC region (R-cm = 3.60 Angstrom) gave a strongly bound BzH(2)O(+) complex as a product, whereas the trajectory from the inner classical turning point (R-cm = 2.95 Angstrom) leads to the dissociation product (Bz(+) + H2O). The reaction mechanism of the ionization processes of the BzH(2)O complex was discussed on the basis of these theoretical results.