Calculated refractivity of water vapor and moist air in the atmospheric window at 10 microm.

The HITRAN 2000 database of infrared line transitions has been used to calculate the dispersion coefficient of water vapor at room temperature in the atmospheric window up to 25 microm, confirming an equivalent earlier compilation [Infrared Phys. 26, 371 (1986)]. I complement this line set by using an previously published ultraviolet pseudospectrum [J. Chem. Phys. 68, 1426 (1978)] to improve coverage of the near infrared. The effect of admixtures of abundant nitrogen, oxygen, and carbon dioxide is predicted on the same calculational basis to synthesize the air representative of the mountain that hosts the Very Large Telescope Interferometer and is found to be small compared with the dominant role of water at wavelengths above 3 microm.