The spectrum of N$_2$ from 4,500 to 15,700 cm$^{-1}$ revisited with PGOPHER

TL;DR

This study extends the molecular nitrogen spectrum up to 15700 cm$^{-1}$, providing a comprehensive line list and spectral models for improved calibration and analysis in various scientific applications.

Contribution

The paper presents an extended nitrogen spectrum up to 15700 cm$^{-1}$, with detailed spectral analysis and models using PGOPHER, including ab initio calculations for enhanced accuracy.

Findings

Extended nitrogen spectrum up to 15700 cm$^{-1}$

Provided detailed line list with transition data

Developed spectral models for simulation and analysis

Abstract

Using a reference molecular atlas to ensure self-consistency of wavelength calibration is widespread practice. Boesch \& Reiners (Astronomy \& Astrophysics 582 A43 (2015)) reported a line list from a discharge of molecular nitrogen from 4500 to 11000 cm$^{-1}$ for this purpose. With a hollow-cathode discharge source, we have extended the experimental spectrum up to 15700 cm$^{-1}$, to include the range of Ti:sapphire lasers, since the density of N 2 lines is greater than atomic atlases in common use. Recognizing that experimental conditions can vary, we have also analysed the spectra (comprising several B ${}^3\Pi_g-A\ {}^3\Sigma_u^+$ , B' ${}^3\Sigma_u - B\ {}^3\Pi_g$, and W ${}^3\Delta_u-B\ {}^3\Pi_g N_2$ bands) with standard Hamiltonians, so that any part of the discharge spectrum 4500-15700 cm$^{-1}$ can be simulated. Parameters are given to do this with the spectral simulation and analysis package PGOPHER. (C. Western, J. Quant. Spectrosc. Rad. Transf., 186, 221 (2016)). The analysis also included high-level ab initio calculations of potential energy curves, transition moments and spin-orbit coupling constants and these were used in preparing the model, extending the potential range of applicability. The results are available in a variety of formats to suit possible applications, including the experimental spectrum in ASCII, a detailed line list with positions and Einstein A coefficients, and a PGOPHER input file to synthesize the spectrum at selectable temperature and resolution. 2