Observation of pure rotational absorption spectra in the nu2 band of hot H(2)O in flames.

We present measurements of absorption spectra of hot-water vapor generated in a propane-air flame in the far-infrared region of the spectrum from 0.1 to 3.5 THz (3.3 to 117cm(-1)). Transitions within the rotational manifold of both the ground and the nu(2)=1 vibrational levels were observed. The measurements are in good agreement with calculations of the predicted absorption spectra at 1300 K based on tabulated line intensities, whereas predicted theoretical line widths were found to be approximately one third too narrow.