Direct determination of the Boltzmann constant by an optical method.
We have recorded the Doppler profile of a well-isolated rovibrational line in the nu(2) band of (14)NH(3). Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant k(B) by laser spectroscopy. A relative uncertainty of 2 x 10(-4) has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin.
Laboratoire de Physique des Lasers, UMR CNRS 7538, Institut Galilée, Université Paris 13, 99, avenue J.-B. Clément, 93430 Villetaneuse, France.
C
C
Daussy
M
M
Guinet
A
A
Amy-Klein
K
K
Djerroud
Y
Y
Hermier
S
S
Briaudeau
Ch J
ChJ
Bordé
C
C
Chardonnet