VUV-synchrotron absorption studies of N$_2$ and CO at 900 K

Abstract

Photoabsorption spectra of N$_2$ and CO were recorded at 900K, using the vacuum-ultraviolet Fourier-transform spectrometer at the DESIRS beamline of synchrotron SOLEIL. These high-temperature and high-resolution measurements allow for precise determination of line wavelengths, oscillator strengths, and predissociative line broadening of highly-excited rotational states with $J$ up to about 50, and also vibrational hot bands. In CO, the perturbation of $A\,{}^1Π-X\,{}^1Σ^+$ vibrational bands $(0,0)$ and $(1,0)$ were studied, as well as the transitions to perturbing optically-forbidden states $e\,{}^3Σ^-$, $d\,{}^3Δ$, $D\,{}^1Δ$ and $a'\,{}^3Σ^+$. In N$_2$, we observed line shifts and broadening in several $b\,{}^1Π_u-X\,{}^1Σ^+_g$ bands due to unobserved forbidden states of ${}^3Π_u$ symmetry. The observed state interactions are deperturbed and, for N$_2$, used to validate a coupled-channels model of the interacting electronic states. This data is appropriate for use in astrophysical or (exo-)planetary atmospheric applications where high temperatures are important and in future spectroscopic models of these molecules.

17 pages, 8 figures, 7 tables