An ab initio investigation of non-adiabatic couplings and conical intersections among the lowest five electronic states of the NO₃ radical

ABSTRACT

In order to explore spectroscopic properties of a floppy molecule, it is necessary to compute accurate diabatic potential energy surfaces (PESs) around the Franck–Condon region of nuclear configuration space. In such cases, it is desirable to include the non-adiabatic coupling terms (NACTs) through Jahn–Teller (JT) and pseudo Jahn–Teller (PJT) effects as well as other accidental conical intersections (CIs) prevailing among the electronic states of the molecule. In this work, we investigate NACTs among the five lowest doublet electronic states of NO₃ radical [ and 2²B₂)], in which all those effects (JT, PJT and CIs) have prominent contributions. The study is carried out in terms of normal modes (Q_is) of NO₃ and the CIs (JT and accidental) are located in a plane of nuclear configuration space of two such coordinates (Q_i and Q_j). We have calculated ab initio adiabatic PESs and NACTs of those five states of NO₃ at the MRCI level as functions of pairwise Q_is. Further, to explore the nature of a given CI in terms of normal coordinates contributing to NACTs within a particular plane Q_i-Q_j, we have performed CP-MCSCF study computing analytic NACTs and characterised their contributions along various Q_ks.

KEYWORDS:

• Adiabatic potential energy surfaces
• non-adiabatic coupling terms
• Jahn–Teller effect
• pseudo Jahn–Teller effect
• conical intersections

Acknowledgments

Bijit Mukherjee (File No: 09/080(0960)/2014-EMR-I) acknowledges CSIR India for research fellowship and Saikat Mukherjee thanks IACS for the same. Subhankar Sardar acknowledges Dr Pabitra Kumar Mishra, Principal, Bhatter College, Dantan for providing research facility in his institution. K. R. Shamasundar acknowledges Satrajit Adhikari and his group members for the discussions and warm hospitality during his collaborative visits to IACS. Satrajit Adhikari acknowledges DST, India, through project no. File No. EMR/2015/001314 for the research funding. Satrajit Adhikari also acknowledges IACS for CRAY supercomputing facility.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

CSIR grant number 09/080(0960)/2014-EMR-I; DST grant number EMR/2015/001314; IACS, India.