Knowledge Bank

The frequencies of the first six rotational transitions of the CO molecule have been measured to an accuracy of $\pm 500Hz$ in the frequency region up to 700 GHz. This high level of accuracy was achieved with the Cologne terahertz spectrometer operated in the sub-Doppler mode (1). To carry out precise CO Lamb-dip measurements, Least squares fits of the new CO, and 0.26 kHz, respectively. The experimental setup and the results of a fit to the Lamb-dip data combined with the frequencies up to 4.3 THz $(J=38\leftarrow 37)$ given by Evenson (3) will be presented. The analysis yielded a revised set of rotational constants for CO in its vibrational ground state, which is in good agreement with the previous values given by Varberg and Evenson(4).