Laser-radiofrequency double-resonance spectroscopy of methyl chloride: Hyperfine structure of the ground and ν6 states

Pure quadrupole resonances of methyl chloride have been observed using the highly sensitive method of infrared-radiofrequency double resonance inside a laser cavity. Quadrupole resonances have been observed for the ground and ν₆ states for both the CH₃Cl³⁵ and CH₃Cl³⁷ isotopes using the direct double-resonance as well as collisionally induced satellites. Most of the six hyperfine constants: the quadrupole coupling constant, eqQ; its rotational dependence, χ_J and χ_K; Hougen's coefficient, χ_D; and the spin-rotation constants, C_N and C_K, have been determined for the two states for both isotopes.