An ab-initio direct trajectory study on the ionization processes of the benzene–NH3 complexes: 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.