An ab-initio direct trajectory study on the ionization processes of the benzene–NH3complexes: Electronic state dependence on the complex formation processes

Abstract

Ionization processes of benzene–ammonia 1 ∶ 1 complex (BzNH3) have been investigated by means of full dimensional direct ab-initio trajectory, ab-initio molecular orbital (MO) and density functional theory (DFT) calculations. The static ab-initio MO calculations showed that a dipole of NH3 orients toward the center-of-mass of Bz in a stable structure of BzNH3. Trajectories on the potential energy surfaces (PESs) for the ground and first excited states of BzNH+3, expressed schematically by Bz(NH+3) and (Bz+)NH3, respectively, were calculated at the UHF/4-21G(d) level. The calculations for the (Bz+)NH3 state indicated that two reaction channels are competitive with each other as product channels. One is the dissociation channel in which the NH3 molecule is directly dissociated from Bz+. The other one is complex formation channel in which the trajectory leads to a strongly bound complex where NH3 is bound to one of the carbon atoms of Bz+ and a N–C bond is newly formed. On the other hand, a weakly bound complex composed of Bz and NH+3 was formed in the ionization to the Bz(NH+3) state. A hydrogen of NH+3 orients toward one of the carbon atoms of Bz. The dissociation product (Bz + NH+3) was not obtained in this state. The mechanism of the ionization of BzNH3 is discussed on the basis of the theoretical results.