Experimental observation of the ν$_{2}$+4ν$_{3}$ bands of HD$^{16}$O and HD$^{18}$O between 14975 and 15275 cm$^{-1}$

The ν$_{2}$+4ν$_{3}$ combination bands of HD$^{16}$O and HD$^{18}$O 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 HD$^{18}$O and HD$^{16}$O 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 HD$^{18}$O and the theoretically predicted lines from the Tomsk database. Similarly for HD$^{16}$O, 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 H$_{2}$$^{16}$O spectra in the region between 15254.2 cm$^{-1}$ and 15376.9 cm$^{-1}$ and corroborated the systematic shifts of the ab initio data. ... mehrA few lines of the ν$_{1}$+4ν$_{2}$+2ν$_{3}$ bands of HD$^{16}$O and HD$^{18}$O were also identified. The data are compared and discussed on basis of existing literature data.