Spectral lines of methane measured up to 2.6 THz at sub-MHz accuracy with a CW-THz photomixing spectrometer: Line positions of rotational transitions induced by centrifugal distortion. (December 2017)

• Record Type: Journal Article
• Authors: Bray, C.; Cuisset, A.; Hindle, F.; Mouret, G.; Bocquet, R.; Boudon, V.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 203(2017)
• Page Start: 349
• Page End: 354
• Publication Date: 2017-12
• Subjects: THz photomixing -- Frequency-comb -- Methane -- Rotational spectroscopy -- Line positions; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2017.04.010
• Languages: English
• ISSNs: 0022-4073

Abstract

Abstract: Several Doppler-limited rotational transitions of methane induced by centrifugal distortion have been measured with an unprecedented frequency accuracy using a THz photomixing synthesizer based on a frequency comb. Compared to previous synchrotron based FT-Far-IR measurements of Boudon et al. (Ref. [1] ), the accuracy of the line frequency measurements is improved by one order of magnitude; this yields a corresponding increase of two orders of magnitude to the weighting of these transitions in the global fit. The rotational transitions in the ν 4 ← ν 4 hot band are measured for the first time by the broad spectral coverage of the photomixing CW-THz spectrometer providing access up to R(5) transitions at 2.6 THz. The new global fit including the present lines has been used to update the methane line list of the HITRAN database. Some small, but significant variations of the parameter values are observed and are accompanied by a reduction of the 1- σ uncertainties on the rotational ( B 0 ) and centrifugal distortion ( D 0 ) constants. Abstract : Highlights: We present new highly accurate measurements of methane rotational lines. We use a THz photomixing synthesizer base on a frequency comb. The measured line are used to improve the spectroscopic parameters of CH4. They have been used for the HITRAN2016 update.