Abstract
We report the first measurement of sub-Doppler molecular response using a frequency comb by employing the comb as a probe in optical-optical double-resonance spectroscopy. We use a 3.3 μm continuous wave pump and a 1.67 μm comb probe to detect sub-Doppler transitions to the 2ν_{3} and 3ν_{3} bands of methane with ∼1.7 MHz center frequency accuracy. These measurements provide the first verification of the accuracy of theoretical predictions from highly vibrationally excited states, needed to model the high-temperature spectra of exoplanets. Transition frequencies to the 3ν_{3} band show good agreement with the TheoReTS line list.
Highlights
Methane is the first organic molecule detected in the atmosphere of hot-Jupiter exoplanets via satellite- and ground-based observations [1,2]
Theoretical spectra can be produced using the parameters from the ExoMol [5,6] or TheoReTS [7,8] line lists obtained from ab initio calculations, but firmly assigned experimental transitions from highly excited levels are needed to judge the accuracy of these predictions
Optical-optical double-resonance (DR) spectroscopy [16] is a powerful tool for assignment of highly excited energy levels [17]
Summary
Methane is the first organic molecule detected in the atmosphere of hot-Jupiter exoplanets via satellite- and ground-based observations [1,2]. Firmly assigned experimental hot band transitions reaching levels above 8000 cm−1 are needed to allow empirical corrections to line positions in the Triacontad range and more accurate modeling of the high-temperature spectra [13,15].
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