Renner-Teller nonadiabatic coupling terms:An ab-initio study of the HNH molecule

摘要

In this Communication we present the first theoreticalumerical treatment of nonadiabatic coupling terms (NACT) that originate from the Renner-Teller (RT) model,namely,those that follow from the splitting of an electronic level of a linear molecule when it becomes bent.These two newly formed states are characterized by different symmetries and are designated as A and B.Our main findings:(1) The RT NACTs are quantized as long as they are calculated close enough to collinear configuration of the molecule (in this case HNH).Their value is tau=1 (the Jahn-Teller values in similar situations,are tau=1/2).(2) Calculation of RT NACTs at bent configurations (i.e.,at a distance from the linear axis) yield decreased values,sometimes by more than 50%.This last finding implies that in strongly bent configurations the two-state Hilbert subspace (formed by the above mentioned A and B states) is affected by upper states,most likely via Jahn-Teller conical intersections.(3) This study has also important practical implications.The fact that the RT NACTs decrease in (strongly) bent situations implies that analyzing spectroscopic data employing only the two PI-states may not be sufficient in order to achieve the required accuracy.