Spectrum of the $^{15}$N$^{17}$O isotopologue in the region of 1.86 $\mu$m. Determination of the “Dunham-type” constants

The absorption spectrum of the $^{15}$N$^{17}$O molecule in the range 5200–5500 cm$^{-1}$ was recorded for the first time using a Bruker IFS-125M Fourier spectrometer with a spectral resolution of 0.0056 cm$^{-1}$. Analysis of the spectrum made it possible to detect the vibration-rotation lines of the 3-0 band of the main transitions in the Х$^2\Pi$ electronic state of the $^{15}$N$^{17}$O molecule. For the main transitions $^2\Pi_{1/2}$ – $^2\Pi_{1/2}$ and $^2\Pi_{3/2}$ – $^2\Pi_{3/2}$, 149 positions of rotational lines were registered in the three branches with the maximum value of the rotational quantum number $J$ = 29.5. It was for the first time possible to determine the parameters of $\Lambda$-splitting in this band. The positions and relative intensities of both the components of the $\Lambda$-doublets and the centers of 31 unresolved doublets were determined. The frequencies of the registered transitions and the transition frequencies in the 1-0 vibrational band, weighted in accordance with experimental uncertainties, were jointly processed using two models. As a result of the processing, spectroscopic parameters were determined for vibrational states $v$ = 0,1,3, as well as “Dunham-type” constants for the $^{15}$N$^{17}$O isotopologue. Using the found “Dunham-type” constants, model calculations of transition frequencies in vibrational bands 1-0, 2-0, 3-0 up to $J$ = 35.5 were performed. A comparison of the calculated transition frequencies with those given in the Exomol project was made.