The 4-0 band of carbon monoxide by high sensitivity Cavity Ring Down spectroscopy near 8200 cm⁻¹

The room temperature spectrum of carbon monoxide in natural isotopic abundance is recorded by Cavity Ring Down Spectroscopy between 8094 and 8317 cm⁻¹. The investigated range covers the low frequency region of the third overtone band centered at 8414 cm⁻¹. The achieved sensitivity of the recordings corresponds to a noise equivalent absorption, α_min~5×10^–12 cm⁻¹. 94 transitions are measured with intensity ranging between 3×10^–27 and 1×10^–30 cm/molecule. They include the first observation of (i) high J lines of the P branch of the 4-0 band of ¹²C¹⁶O, (ii) the 4-0 band of ¹³C¹⁶O and ¹²C¹⁸O present in natural abundance in the sample (35 and 38 transitions, respectively), (iii) a few lines of the 4-0 band of ¹²C¹⁷O and of the 5-1 hot band of ¹²C¹⁶O. The spectroscopic parameters of the v=4 upper level of ¹³C¹⁶O and ¹²C¹⁸O are obtained from a fit of the measured line positions. The line positions reported with an accuracy of 5×10⁻⁴ cm⁻¹ and the derived line intensities are used for comparison to various theoretical line lists of carbon monoxide available in the literature. The agreement between the obtained experimental data and the most recent theoretical line lists available in the literature is discussed. - Highlights: • Detection of 94 transitions of the 4-0 band of CO between 8094 and 8317 cm⁻¹. • CRDS spectra recorded at room temperature and low pressure (5 and 10 Torr). • The noise equivalent absorption of the spectra is α_min≈5×10⁻¹² cm⁻¹. • First observation of the 4-0 band of ¹³C¹⁶O, ¹²C¹⁸O and ¹²C¹⁷O. • Critical comparison to the available calculated line lists of carbon monoxide