Experimental observation of the ν₂+4ν₃ bands of HD¹⁶O and HD¹⁸O between 14975 and 15275 cm⁻¹

The ν₂+4ν₃ combination bands of HD¹⁶O and HD¹⁸O were measured using Fourier transform-incoherent broadband cavity-enhanced absorption spectroscopy (FT-IBBCEAS) with a spectral resolution of 0.08 cm⁻¹. The ro-vibrational lines of these bands were assigned through comparison with ab-initio molecular lines from the Tomsk variational calculation database (http://spectra.iao.ru/). For HD¹⁸O and HD¹⁶O in total 114 and 141 strong lines were assigned in the region between 14975.3 cm⁻¹ and 15243.3 cm⁻¹ and between 14998.5 cm⁻¹ and 15274.7 cm⁻¹, respectively. While the very satisfactory agreement of line intensities was used for line assignments, a systematic average discrepancy of ~0.305 cm⁻¹ in line positions was identified between the measured lines of HD¹⁸O and the theoretically predicted lines from the Tomsk database. Similarly for HD¹⁶O, an approximate wavenumber difference of ~0.361 cm⁻¹ was observed. The wavenumber accuracy of the Fourier transform cavity enhanced absorption spectrometer was confirmed on basis of concurrently measured H₂¹⁶O spectra in the region between 15254.2 cm⁻¹ and 15376.9 cm⁻¹ and corroborated the systematic shifts of the ab initio data. A few lines of the ν₁+4ν₂+2ν₃ bands of HD¹⁶O and HD¹⁸O were also identified. The data are compared and discussed on basis of existing literature data.