Conical intersections involving the lowest 1πσ* state in aniline: Role of the NH2 group

At low excitation energies of under 5 eV, conical intersections (CIs) involving the lowest three electronic states of aniline, viz. the (1)pi pi*/(1)pi sigma* and (1)pi sigma*/GS intersections, are accessible. Signatures of ultrafast dynamics, including H atom loss, are observed experimentally with energies above the (1)pi sigma* threshold. Ab initio results corroborate the view that the intersections are involved in the rapid population flow. In the present computational study, we characterize these intersections using the CASSCF and XMS-CASPT2 methods. We locate the CIs and analyse the important vibronic couplings at these geometries from a normal mode as well as an NH2 local mode perspective. Through our findings, we suggest that modes largely local to the NH2 group couple the electronic states the strongest at these intersections. (C) 2018 Elsevier B.V. All rights reserved.