It was suggested earlier (А.F. Krupnov et al. // Atmospheric and Oceanic Optics, 20, No. 9, 772–776 (2007)) to observe individual rotational lines of water dimer at high resolution in millimeter and submillimeter wave range in order to reveal a water dimer spectrum in equilibrium gas state; and a sufficient sensitivity of some microwave spectrometers for observation of the dimer lines with the absorption coefficient, calculated by us, was demonstrated. In the present paper we consider conditions of such observation of the dimer individual line against the background of sum water vapor absorption in millimeter range. It is shown that calculated intensity of an individual rotational line of the dimer is just a few times smaller that a total merged absorption of water vapor, and that the dimer absorption constitutes a major fraction of the total observed water vapor absorption in millimeter wave range. This means that the direction of research suggested earlier seems promising for revealing the water dimer in equilibrium state the problem, which many researchers try to solve during last forty years.
water dimmer; continual absorption; equilibrium conditions; millimeter waves