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

Abstract 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.