Hyperfine-resolved 3.4-μm spectroscopy of CH₃I with a widely tunable difference frequency generation source and a cavity-enhanced cell: A case study of a local Coriolis interaction between the v₁=1 and (v₂,v6l)=(1,22) states

Saturated absorption spectra of the ν₁ fundamental band of CH₃I are recorded with a cavity-enhanced cell and a tunable difference frequency generation source having an 86-cm^-1 range. The recorded spectral lines are 250 kHz wide, and most of them are resolved into the individual hyperfine components. The Coriolis interaction between the v ₁=1 and (v₂,v6l)=(1,22) states locally perturbing the hyperfine structures is analyzed to yield the Coriolis and hyperfine coupling constants with uncertainties similar to those in typical microwave spectroscopy. The spectrometer has demonstrated the potential for precisely determining the energy structure in the vibrational excited states.