Knowledge Bank

Pure rotational transitions of methane in the $\nu 3$ state have been observed by infrared-microwave double resonance spectroscopy. A total of 15 transitions among the tetrahedral fine structure components of the Coriolis sublevels were measured. A tunable color center laser was used as the infrared radiation source, and a synthesized centimeter wave signal generator operating between 11.5 and 17.5 GHz was used as the microwave source. The frequencies, measured to better than 50 kHz, are compared to frequencies calculated from combination differences of the most precise infrared frequencies.