Abstract-Pure rotation spectrum of CF4 in the v3 = 1 state using THz synchrotron radiation

V. Boudon, M. Carlos, C. Richard,  O. Pirali,

https://www.sciencedirect.com/science/article/pii/S0022285217302783

Spherical-top tetrahedral species like CH4, SiH4, CF4, …possess no permanent dipole moment. Therefore, probing their pure rotation spectrum is very challenging since only a very weak dipole moment can be induced by centrifugal distortion and/or rovibrational interaction. If some Q branch lines have been recorded thanks to microwave techniques, R branch lines in the THz region have been poorly explored until recently. In previous studies, we have reported the pure rotation THz spectrum of cold and hot band lines of methane recorded at the SOLEIL Synchrotron facility. Here, we present the first recorded THz spectrum of the R branch of CF4, a powerful greenhouse gas, in its ${}_{\mathrm{}}\mathrm{}$ state. This Fourier transform spectrum covers the $\mathrm{}$ to $\mathrm{}$ line clusters, in the 20–37 cm−1 spectral range. It was recorded thanks to a 150 m multiple path cell at room temperature. We could estimate the vibration-induced dipole moment value and also include the recorded line positions in a global fit of many CF4 transitions.

Abstract-Pure rotation spectrum of CF4 in the v3 = 1 state using THz synchrotron radiation

V. Boudon, M.Carlos, C.Richard, O.Pirali,

https://www.sciencedirect.com/science/article/pii/S0022285217302783

     (We present the first recorded THz spectrum of the R branch of CF4, a powerful greenhouse gas, in its v3 = 1 state. We could estimate the vibration-induced dipole moment value and also include the recorded line positions in a global t of many CF4 transitions.)


Spherical-top tetrahedral species like CH4, SiH4, CF4, …possess no permanent dipole moment. Therefore, probing their pure rotation spectrum is very challenging since only a very weak dipole moment can be induced by centrifugal distortion and/or rovibrational interaction. If some Q branch lines have been recorded thanks to microwave techniques, Rbranch lines in the THz region have been poorly explored until recently. In previous studies, we have reported the pure rotation THz spectrum of cold and hot band lines of methane recorded at the SOLEIL Synchrotron facility. Here, we present the first recorded THz spectrum of the R branch of CF4, a powerful greenhouse gas, in its $v_3=1$ state. This Fourier transform spectrum covers the $R(20)$ to $R(37)$ line clusters, in the 20–37 cm−1spectral range. It was recorded thanks to a 150 m multiple path cell at room temperature. We could estimate the vibration-induced dipole moment value and also include the recorded line positions in a global fit of many CF4 transitions.

Abstract-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

• C. Bray^a, 
• A. Cuisset^a, 
• F. Hindle^a, 
• G. Mouret^a, 
• R. Bocquet^a, 
• V. Boudon^b

• ^a Laboratoire de Physico-Chimie de l'Atmosphàre, CNRS EA-4493 - Université du Littoral Côte d'Opale, 59140 Dunkerque, France
• ^b Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS - Université Bourgogne Franche-Comté, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France
• 
  

http://www.sciencedirect.com/science/article/pii/S0022
40731730047X

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 ν₄←ν₄${}_{\mathrm{}}{}_{\mathrm{}}$ 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 (B₀) and centrifugal distortion (D₀) constants.