Heterodyne techniques have been used to experimentally determine, for the first time, the frequencies for nineteen laser emissions ranging from 264 to 984 GHz. These laser emissions were generated by optically pumping either CH3CN, CD3CN, $^{13}\textit {CH}_{3}$
13
CH
3
I, CD3I, or $^{13}\textit {CD}_{3}$
13
CD
3
I with a CO2 laser. This includes the newly discovered 566.325-μ m laser emission from optically pumped $^{13}\textit {CD}_{3}$
13
CD
3
I. The fractional uncertainties with which these frequencies were experimentally determined, up to ± 5 × 10− 7, were of sufficient accuracy to confirm or revise seven previously proposed far-infrared laser assignments.