Experimental observation of the v(2)+4v(3) bands of (HDO)-O-16 and (HDO)-O-18 between 14975 and 15275 cm(-1)

The v(2)+4v(3) combination bands of (HDO)-O-16 and (HDO)-O-18 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 (HDO)-O-18 and (HDO)-O-16 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 similar to 0.305 cm(-1) in line positions was identified between the measured lines of (HDO)-O-18 and the theoretically predicted lines from the Tomsk database. Similarly for (HDO)-O-16, an approximate wavenumber difference of similar to 0.361 cm(-1) was observed. The wavenumber accuracy of the Fourier transform cavity enhanced absorption spectrometer was confirmed on basis of concurrently measured (H2O)-O-1-O-6 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 v(1)+4v(2)+2v(3) bands of (HDO)-O-16 and (HDO)-O-18 were also identified. The data are compared and discussed on basis of existing literature data. (C) 2020 The Authors. Published by Elsevier Inc.