Microwave spectrum of the vibrational excited states ν6 and ν8 of formic acid: Contribution to the assignment of the Formic Acid Submillimeter Laser

The microwave spectrum of the ν₆ and ν₈ vibrationally excited states of H¹²COOH has been reinvestigated in the 10–200-GHz region, and 23 new transitions, essentially of the b type, were measured. The transitions allowed us to obtain a set of improved parameters for each of these two states which contribute to the assignment of the Formic Acid Submillimeter Laser. The vibrational energies of the ν₆ and ν₈ states have been derived from the assignment of infrared pump transitions and the corresponding submillimeter transition of the optically pumped submillimeter laser.