Precise Frequency Measurements Of The 2ν₃ A₁ - ν₃ Band Transitions Of Methane With Comb-referenced Infrared-infrared Double-resonance

We have carried out infrared-infrared double-resonance spectroscopy of the 2\nub{3} A$_{1}$ - \nub{3} band of methane. The \nub{3} band transitions are pumped using a 90.5 THz difference-frequency-generation (DFG) source frequency-controlled with an optical frequency comb (OFC), and ten tetrahedral components of the Q(1) to Q(4) transitions from the pumped levels are observed with a half-width at half maximum of 0.43 MHz using another 88.5 THz DFG source. The transition frequencies are determined with an uncertainty of 10 kHz using the OFC