The analysis of a spectrum of 15N18O molecule recorded in the region 5100–5500 cm−1 was performed, and 187 positions of rotational lines were found in the vibrational band 3–0 of the main transitions between the electronic states 2Π1/2 and 2Π3/2 with the maximal rotational quantum number J = 32. 5. For the first time, Λ-splitting was observed in this band. The positions and relative intensities of both the resolved component of Λ-doublets and unresolved doublets were determined. A joint weighted processing of all known vibrational-rotational transition frequencies in the microwave and infrared spectral regions was carried out. As a result, Dunham type constants were determined for 15N18O isotopologue in the ground electronic state. Using the found constants, predictive calculations of the rotational line positions of all bands corresponding to vibrational transitions between states with v ≤ 3 and J ≤ 37. 5 were carried out. The experimental data obtained in this study provide new spectroscopic information about 15N18O isotopologue and enrich fundamental knowledge about nitrogen monoxide molecule.
Borkov et al. (Wed,) studied this question.