Precision measurements of NH_3 spectral lines near 11 μm using the infrared heterodyne technique

Abstract
Absolute line-center frequencies for eleven lines of ammonia in near coincidence with CO2-laser transitions have been determined to accuracies of ±3 MHz by infrared heterodyne detection. These results were obtained by heterodyning a blackbody with a stable, grating-tuned CO2 gas laser. A discussion of the apparatus and method of calculation, including error analysis, is presented. With these accurately determined line-center positions, the ammonia molecule will be a useful secondary-frequency standard for diode-laser spectroscopy in the 11-μm wavelength region.