Accurate Einstein coefficients for electric dipole transitions in the first negative band of N₂⁺

¹ Groupe de Spectrométrie Moléculaire et Atmosphérique, GSMA, UMR CNRS 7331, U.F.R. Sciences Exactes et Naturelles, University of Reims Champagne-Ardenne, 51100 Reims, France
e-mail: olfa.ferchichi@univ-reims.fr; alexander.alijah@univ-reims.fr
² Laboratoire de Spectroscopie Atomique, Moléculaire et Applications, LSAMA, Departement of Physics, Faculty of Sciences, University of Tunis – El Manar, 1060 Tunis, Tunisia
e-mail: najoua.derbel@gmail.com
³ Institut UTINAM, UMR 6213 CNRS-Univ. Bourgogne Franche-Comté, OSU THETA, BP 1615, 25010 Besançon Cedex, France

Received: 8 December 2021
Accepted: 14 February 2022

Abstract

Context. The N₂⁺ fluorescence spectrum of comet C/2016 R2 is modelled in a companion paper. That work relies on accurate Einstein coefficients for electric dipole transitions between the B²∑_u⁺ and X²∑_g⁺ electronic states of N₂⁺.

Aims. These coefficients are provided in the present paper.

Methods. The potential energy curves and transition dipole moments were computed at a high level of ab initio theory and include relativistic corrections. Rovibrational wavefunctions were then obtained without assuming separability of vibrational and rotational motions.

Results. Vibrationally and rotationally resolved Einstein coefficients are presented in a convenient three-parameter functional form for three isotopologues. A possible explanation is given for the large variation in the experimental radiative lifetimes.