Laboratory Precision Measurements of the Rotational Spectrum of12C17O and13C17O

Abstract

High-precision millimeter and submillimeter wave measurements were performed on two 17O isotopically substituted carbon monoxide species, i.e., 12C17O and 13C17O. Covering the frequency region from 100 GHz to 1 THz, the accuracy achievable is estimated to be ±5 kHz in the Doppler-limited mode and ±1 kHz for sub-Doppler-resolution measurements. From a weighted least-squares fit, the following molecular rotational parameters for 12C17O and 13C17O were obtained: for 12C17O, and for 13C17O, in both instances, the H0 values were kept fixed to IR data. The oxygen 17O nucleus exhibits a sizeable electric nuclear quadrupole moment, which has been measured for both isotopomers, i.e., eQq(12C17O) = 4.298(44) MHz and eQq(13C17O) = 4.355(182) MHz. The high precision of the Lamb dip measurements allowed us to observe additional small hyperfine effects caused by the magnetic moment of the 17O nucleus. These precision measurements allowed the determination of the nuclear spin-rotation constant CI(17O) = -31.60(72) Hz for 12C17O, solely from the Cologne data set. The highly precise transition frequencies reported here should warrant deep interstellar searches for the two molecules 12C17O and 13C17O. The latter has not been detected in space until very recently. On the basis of our laboratory data, we were able to report the discovery of 13C17O (by Bensch and coworkers) along with the observations of two additionalrare CO isotopomers including 12C17O and 12C18O toward core C of the ρ Ophiucus molecular cloud.