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Published online by Cambridge University Press: 03 August 2017
In interstellar clouds, where “thermal” /nonmaser/ OH emission in the 18-cm lines is observed, prominent anomalies of the intensities of the two satellite lines, 1612 and 1720 MHz, are often seen. If a cloud is observed against a background source of radio continuum, then one satellite may be in strong absorption, while the other one is in emission almost as strong as that in the main lines, 1665 and 1667 MHz. In those clouds, for which several positions were observed in the OH lines, the roles of the satellites are sometimes interchanged with the displacement along the cloud. At the same time, the main lines usually have the intensity ratio close to the equilibrium one. This behaviour indicates to deviations of the level populations of OH molecules from the Boltzmann ones.