On the Uncertainty of the Calculated Intensities of Water Vapor Lines in the Sub-THz Frequency Range

A comparative analysis of open source data on the water spectral lines intensities in the frequency range from 0 to 1.75 THz was carried out. The analyzed data are significant for radiation propagation models. The calculations by the method of effective Hamiltonians and the variational method, as well as experimental data were taken into account. The uncertainty of intensity was found to be less than 2% for lines of the ground vibrational state with an intensity of more than 10⁻²⁷ cm/molecule and about 5–10% for weaker lines. For strong (more than 10⁻²⁶ cm/molecule) rotational lines of the ν₂ state, the intensity uncertainty ranged from 2 to 5% and increased up to 5–10% for weak lines. For all rotational lines of the 2ν₂, ν₁, and ν₃ states, the uncertainty was no more than 5–10%. The presented data show that most of the considered lines can be assigned a higher (by 1–2 steps according to the classification adopted in HITRAN) category of intensity accuracy.