Predissociation mechanism for the lowest Πu1 states of N2

Abstract

Separate coupled-channel Schrödinger-equation (CSE) models of the interacting (1)Pi(u) (b,c,o) and (3)Pi(u) (C,C(')) states of N(2) are combined, through the inclusion of spin-orbit interactions, to produce a five-channel CSE model of the N(2) predissociation. Comparison of the model calculations with an experimental database, consisting principally of detailed new measurements of the vibrational and isotopic dependence of the (1)Pi(u) linewidths and lifetimes, provides convincing evidence that the predissociation of the lowest (1)Pi(u) levels in N(2) is primarily an indirect process, involving spin-orbit coupling between the b (1)Pi(u)- and C (3)Pi(u)-state levels, the latter levels themselves heavily predissociated electrostatically by the C(') (3)Pi(u) continuum. The well-known large width of the b(v=3) level in (14)N(2) is caused by an accidental degeneracy with C(v=9). This CSE model provides the first quantitative explanation of the predissociation mechanism for the dipole-accessible (1)Pi(u) states of N(2), and is thus likely to prove useful in the construction of realistic radiative-transfer and photochemical models for nitrogen-rich planetary atmospheres.

Photodissociation of interstellar N2

“…The predissociation efficiency η is then given by η = 1−τ tot /τ rad , where τ tot is the inverse of the sum of the radiative and predissociation rates. For almost all transitions, η 1: significant corrections for partial dissociation are needed only for the b − X(1, 0) and c − X(0, 0) bands near 986 and 959 Å, respectively (Lewis et al 2005b;Liu et al 2008;Sprengers et al 2004;Wu et al 2012). For example, the top panel of Fig.…”

High-resolution Fourier-transform extreme ultraviolet photoabsorption spectroscopy of 14N15N

“…33 Information on f values and predissociation rates of the secondary isotopomers is very limited but comparison with common bands of 14 N 2 shows large differences in the observed energy-level perturbations and predissociation rates. 34,35 On the theoretical side, the seemingly erratic ordering of bands appearing in the N 2 XUV spectrum was finally explained by assignment to a minimal series of 1 + u and 1 u states which are mutually perturbed by strong homogeneous Rydberg-Valence interactions. 12,36,37 This basic theoretical picture culminated in a much later paper 38 which provided a seminal quantitative model of the N 2 spectrum by solution of the coupled-channel Schrödinger equation (CSE).…”

“…41,42 The ab initio calculation of electronic-transition moments connecting the excited 1 + u and 1 u states with the ground state allowed for the reproduction of the 14 N 2 optical-absorption spectrum as it was then known. 43 A more recent CSE model built upon the previous theoretical work and more recent experimental data provided a new quantitative understanding of the energy-level structure and predissociation mechanism of 1 u levels, 34,44 including rotational and isotopic effects. This work required the inclusion of a series of homogeneously interacting 3 u states, some of which are dissociative, and are spin-orbit coupled to the singlet manifold.…”

Photodissociation and chemistry of N2in the circumstellar envelope of carbon-rich AGB stars

“…We here employ the latest reported photodissociation rate and shielding functions for N 2 (Li et al 2013;Heays et al 2014) to investigate the effects in a chemical model of the CSE of IRC +10216. These are based on a concerted laboratory (e.g., Ajello et al 1989;Helm et al 1993;Sprengers et al 2004;Stark et al 2008;Lewis et al 2008a;Heays et al 2011) and theoretical (e.g., Spelsberg & Meyer 2001;Lewis et al 2005;2008b;Ndome et al 2008) effort over the last two decades. An update was also made to the photodissociation of CO using the selfshielding functions from Visser et al (2009) following a similarly large experimental effort over the past decades.…”