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, αmin~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