Experimental observation of the ν$_1$+3ν$_3$ combination bands of $^{16}$O$^{14}$N$^{18}$O and $^{18}$O$^{14}$N$^{18}$O in the near infrared spectral region

The first observation of the ν$_1$+3ν$_3$ combination band of the nitrogen dioxide isotopologue $^{16}$O$^{14}$N$^{18}$O is presented. The band was measured using Fourier-Transform Incoherent Broad-Band Cavity Enhanced Absorption Spectroscopy (FT-IBBCEAS) in the region between 5870 cm$^{−1}$ and 5940 cm$^{−1}$. To confirm the assignment, the band was simulated using a standard asymmetric top Watson Hamiltonian using extrapolated rotational and centrifugal distortion constants. Furthermore, the first experimental observation of the ν$_1$+3ν$_3$ band of the $^{18}$O$^{14}$N$^{18}$O isotopologue is also reported. The positions of ro-vibrational lines of the ν$_1$+3ν$_3$ band of the naturally most abundant isotopologue $^{16}$O$^{14}$N$^{16}$O were used for wavenumber calibration of line positions.