Frequency metrology in the near-infrared spectrum of H172O and H182O molecules: Testing a new inversion method for retrieval of energy levels

Abstract

An extensive Doppler-free spectroscopic investigation of the nearinfrared absorption spectrum of the H182O molecule was performed, for the first time, with absolute frequency calibration by using a GPS-disciplined fiberbased optical frequency comb. The investigated line pairs belong to the V1 + V3 band and have been chosen in the wavelength range from 1.38 to 1.41μm with a lambda scheme, so as to share the excited energy level and allow an accurate determination of the rotational energy separations of the fundamental vibrational state. The measurement of the sub-Doppler line-center frequencies, also extended to the H172O spectrum, has been performed with an overall uncertainty of ∼ 30 kHz, i.e. about three orders of magnitude lower than the HITRAN data set. The retrieved energy separations agree, by less than 80 kHz, with recent findings provided by the so-called MARVEL procedure for spectral data inversion, thus yielding a very stringent test of its accuracy. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.