The Boltzmann constant from the shape of a H2 18O vibration-rotation line

Eugenio Fasci, Maria Domenica De Vizia, Luigi Moretti, Antonio Castrillo, Livio Gianfrani

Abstract

We report on the recent determination of the Boltzmann constant, kB, by means of Doppler broadening thermometry, performed at the Second University of Naples, providing complementary information, as compared to previous papers. This relatively new method of primary gas thermometry was implemented by using a pair of offset-frequency locked extended-cavity diode lasers at 1.39 m, to probe a particular vibration-rotation transition of the H2 18O molecule. Adopting a rather sophisticated and extremely refined line shape model in the spectral analysis procedure, we were able to determine the Doppler width from high-quality absorption spectra with unprecedented accuracy. Our spectroscopic determination of kB exhibits a combined (type A plus type B) uncertainty of 24 parts over 106.

Keywords

Fundamental Metrology, Laser Spectroscopy, Spectral Line Shapes, Boltzmann Constant

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DOI

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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