Experimental observation of the ν₁+3ν₃ combination bands of ¹⁶O¹⁴N¹⁸O and ¹⁸O¹⁴N¹⁸O in the near infrared spectral region

The first observation of the ν₁+3ν₃ combination band of the nitrogen dioxide isotopologue ¹⁶O¹⁴N¹⁸O 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 ν₁+3ν₃ band of the ¹⁸O¹⁴N¹⁸O isotopologue is also reported. The positions of ro-vibrational lines of the ν₁+3ν₃ band of the naturally most abundant isotopologue ¹⁶O¹⁴N¹⁶O were used for wavenumber calibration of line positions.