Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett Research paper The valence and ion-pair states of the N 2 I 2 van der Waals complex V.V. Baturo, R. Kevorkyants, S.S. Lukashov, S.S. Onishchenko, S.A. Poretsky, A.M. Pravilov ⁎ Department of Physics, Saint Petersburg State University, SPbSU, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia HIGHLIGHTS • The N 2 I 2 (E0 + g ) van der Waals complexes have been studied for the frst time. • Potential parameters of the N 2 I 2 (E;v E =0,3;n E ) complexes have been determined. • Binding energies of the N 2 I 2 (X0 + g and B0 + u ,v B =19) complexes have been estimated. • Ab initio calculation for the N 2 I 2 (X) complex have been performed. ABSTRACT The N 2 I 2 (E + 0 g ) van der Waals complexes have been observed and studied for the frst time. Analysis of the luminescence excitation spectra as well as luminescence spectra themselves in the spectral ranges, where the I 2 (D + 0 u → X + 0 g , β1 g → A1 u and D’2 g → A’2 u ) transitions can occur, has been carried out. Branching ratios of the iodine molecule state formation and vibronic level population have been determined. Ab initio calculations of the N 2 I 2 (X + 0 g ) complex ground state at complete basis set limit are performed. It is shown that it has two stable, parallel and linear, isomers separated by an energy barrier. The parallel isomer is observed in our experiments. Binding energies of the N 2 I 2 (X + 0 g ,v X =0,n X =0, B + 0 u ,v B =19,n B = 0) as well as the some spectroscopic parameters of the N 2 I 2 (E,v E =0, 3) complexes have been also estimated. 1. Introduction Many studies of triatomic van der Waals (vdW) complexes have been carried out. They turned out to be ideal model systems for an understanding of energy transfer processes and weak intermolecular forces. Spectroscopic characteristics, potential energy surfaces (PESs) as well as dynamics of rare gas-dihalogen complexes, RgXY, have been extensively studied both in experimental (see [1–4] and references) and theoretical works (see [5–7] and references). As to vdW complexes of XY and molecules, to the best of our knowledge, there are four papers in which H 2 I 2 ,D 2 I 2 ,N 2 I 2 ,andHeN 2 I 2 vdW complexes have been studied. Kenny et al. [8] studied fuores- cence excitation as well as fuorescence spectra ofH 2 I 2 (B + 0 u ,v B =16, 20–23, 26, 27) and D 2 I 2 (B + 0 u ,v B =16, 20–23, 26, 27) complex vibra- tional predissociation (VP) products. They determined binding energies of the complexes in the ground and excited states as well as VP product state distributions and lifetime of the H 2 I 2 (B) state. M. Gutman et al. report on picoseconds time-resolved studies of the H 2 I 2 (B + 0 u ,v B =17) VP [9]. Johnson and Levy [10] studied fuorescence excitation as well as fuorescence spectra ofN 2 I 2 (B + 0 u ,v B =21) and HeN 2 I 2 (B + 0 u ) complex VP products. They showed that the = + + + B v B v v NI(0, 21) N I(0, ), u B u B B 22 2 2 Δv B ≥3, VP channels are possible, only, and binding energies of the N 2 I 2 (B + 0 u ,v B =21) and N 2 I 2 (X + 0 g ,v X =0) complexes are (188–284) cm −1 and (218–313) cm −1 , respectively. Beattie et al. [11] measured (2+1) REMPI spectrum of the [ 2 Π 1/2 ] c 6s;1 g Rydberg state of the N 2 I 2 complex and determined some spectroscopic constants of the complex Rydberg as well as ground states. Recently, we started a program of studies of RgI 2 vdW complexes, Rg=He, Ne, Ar, Kr in ion-pair (IP) states using supersonic molecular beam technique and two-step two-color optical-optical double re- sonance (OODR) excitation scheme [12–16]. We observed lumines- cence of products of the VP and electronic predissociation (EP) of the RgI 2 (X + 0 g ) complexes, determined vibrational populations and branching ratios of the VP and EP products (relative contributions of diferent decay channels to the total decay rate), estimated binding energies of the complexes and several spectroscopic constants of the vdW stretching mode of KrI 2 (E) complex. Luminescence of the HeI 2 (E) and NeI 2 (E) complexes was observed. In this letter, we report on frst observation and study oftheN 2 I 2 (X, B and E)vdWcomplexes. Ab initio calculationsoftheN 2 I 2 (X + 0 g )complex ground state at the complete basis set limit are performed. It is shown https://doi.org/10.1016/j.cplett.2018.10.084 Received 12 September 2018; Received in revised form 31 October 2018; Accepted 31 October 2018 ⁎ Corresponding author. E-mail address: a.pravilov@spbu.ru (A.M. Pravilov). Chemical Physics Letters 714 (2019) 213–218 Available online 02 November 2018 0009-2614/ © 2018 Elsevier B.V. All rights reserved. T