ROTATIONAL SPECTROSCOPY OF VIBRATIONALLY EXCITED N2H+ and N2D+ UP TO 2 THZ

Terahertz absorption spectroscopy was employed to extend the measurements on the pure rotational transitions of N$_2$H$^+$, N$_2$D$^+$ and their $^{15}$N-containing isotopologues in the ground state and first excited vibrational states for the three fundamental vibrational modes. In total 88 new pure rotational transitions were observed in the range of 0.7--2.0~THz. The observed transition frequencies were fit to experimental accuracy, and the improved molecular parameters were obtained. The new measurements and predictions will support the analysis of high-resolution astronomical observations made with facilities such as SOFIA and ALMA where laboratory rest frequencies with uncertainties of 1 MHz or smaller are required for proper analysis of velocity resolved astrophysical components