Speed-dependent effects in NH3 self-broadened spectra: Towards the determination of the Boltzmann constant.

In this paper we present an accurate analysis of the shape of an isolated rovibrational ammonia line from the strong &ngr;2 band around 10 &mgr;m, recorded by laser absorption spectroscopy. Experimental spectra obtained under controlled temperature and pressure are confronted to various models that take into account Dicke narrowing or speed-dependent effects. Our results show a deviation from the Voigt profile probably dominated by speed-dependent broadening and shifting. Accurate line-shape parameters of the &ngr;2 saQ(6,3) line are obtained. Our current project aiming at measuring the Boltzmann constant, kB, by laser spectroscopy will immediately benefit from such knowledge. We anticipate that an optical determination of kB with a competitive uncertainty of a few parts per million is now reachable. [ABSTRACT FROM AUTHOR]