F. Matsushima et al., H2O - A FREQUENCY AND WAVELENGTH STANDARD FROM 0.5 TO 5 THZ (18-160 CM(-1)), IEEE transactions on instrumentation and measurement, 44(2), 1995, pp. 110-112
Frequencies of H2O pure rotational transitions from 0.5 to 5 THz have
been measured with an accuracy of 1 part in 10(8) using a tunable far-
infrared spectrometer. Measured frequencies of more than a hundred spe
ctral lines provide an excellent wavelength and frequency calibration
standard for the far infrared.