An ab-initio direct trajectory study on the ionization processes of the benzene-NH3 complexes:: Electronic state dependence on the complex formation processes

Ionization processes of benzene ammonia 1 : 1 complex (BzNH(3)) 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 BzNH(3). Trajectories on the potential energy surfaces (PESs) for the ground and first excited states of BzNH(3)(+), expressed schematically by Bz(NH3+) 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 NH3+ was formed in the ionization to the Bz(NH3+) state. A hydrogen of NH3+ orients toward one of the carbon atoms of Bz. The dissociation product (Bz + NH3+) was not obtained in this state. The mechanism of the ionization of BzNH(3) is discussed on the basis of the theoretical results.