Stark effects in the ν_3 band of methane

Abstract

Sub-Doppler resolution Stark-modulation spectra of 20 transitions in the ν3 band of methane have been recorded using a difference-frequency-generation source referenced to an optical frequency comb with a frequency uncertainty of a few kilohertz. First-order Stark shifts in the vibrational excited (v3=1) and ground states have been measured separately in the presence of an electric field up to 31 kV/cm. The observed spectra have been analyzed, taking into account the mixing of the vibration–rotation wave functions due to high-order vibration–rotation interactions. The permanent electric dipole moment constants induced by the vibration, rotation, and Coriolis-type terms in the v3=1 state, and those induced by rotation in the vibrational ground state, are determined as Pvib=−16.82(7) mDebye, Prot′=18.6(4) μDebye, PCor=10.4(17) μDebye, and Prot′′=24.47(12) μDebye.