We report what is believed to be the first measurement of rotational line broadening of high-temperature water vapor for transition frequencies that range from 1.0 to 2.5 THz (33 to 83 cm<sup>−1</sup>). Water-vapor rotational transitions were measured in a near-stoichiometric propane–air flame at 1490 K with THz time-domain spectroscopy. Linewidths were measured for 29 pure rotational transitions in both ground vibrational and ν<sub>2</sub>=1 vibrational levels with lower state energies ranging from 80 to 2390 cm<sup>−1</sup>. Measured widths show a dependence on rotational state energy that roughly follows a thermal distribution with variation between various J, K<sub>a</sub>, K<sub>c</sub> rotational quantum numbers.
© 1999 Optical Society of America
(300.6240) Spectroscopy : Spectroscopy, coherent transient
(300.6270) Spectroscopy : Spectroscopy, far infrared
(300.6390) Spectroscopy : Spectroscopy, molecular
(320.7150) Ultrafast optics : Ultrafast spectroscopy
R. A. Cheville and D. Grischkowsky, "Far-infrared foreign and self-broadened rotational linewidths of high-temperature water vapor," J. Opt. Soc. Am. B 16, 317-322 (1999)