Coriolis-dependent Stark effect of the 2ν3 band of methane observed by saturated absorption spectroscopy

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Abstract
We studied the vibration‐induced dipole moment of methane by observing Stark‐modulation spectra of the 2ν3 band centered at 1.66 μm. The spectral purity of an external cavitysemiconductor laser and radiation density in a Fabry–Perot cavity absorption cell are sufficiently high to record sub‐Doppler saturated absorption lines with a spectral resolution of 0.8 MHz. First‐order Stark shifts of the E‐type symmetry components in the P(2), Q(2), Q(4), Q(5), R(2), R(4), and R(5) transitions were measured, and the vibration‐induced dipole moments for the v 3=2 state were determined. Their values clearly demonstrate the Coriolis‐induced dipole term, yielding [5.79(5)+0.440(18)×(2L−3)] mD for the J R level, where L is defined to be −(R+1), 0, and R for the R=J−1, J, and J+1 levels, R and J are rotational and total angular momentum quantum numbers, and numbers in parentheses are 90% confidence intervals in unit of the last digit.