The spectrum of N₂ from 4,500 to 15,700 cm⁻¹ revisited with PGOPHER

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 11,000 cm⁻¹ for this purpose. With a hollow-cathode discharge source, we have extended the experimental spectrum up to 15,700 cm⁻¹, to include the range of Ti:sapphire lasers, since the density of N₂ lines is greater than atomic atlases in common use. Recognizing that experimental conditions can vary, we have also analysed the spectra (comprising several B³Π_g−A³Σ_u ⁺, B^{′ 3}Σ_u ⁻−B³Π_g, and W³Δ_u −B³Π_gN₂ bands) with standard Hamiltonians, so that any part of the discharge spectrum in the range 4,500–15,700 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.