The asymptotic line wing theory assumes the presence of two intermolecular interaction characteristics–quantum and classical intermolecular interaction potentials–in the expression of the absorption coefficient. The same classical potential enters into the expression for the second virial coefficient. The classical potential found from the second virial coefficient data is used for calculating of the temperature dependence of the absorption coefficient of water vapor line wings in the 8–12 μm transparency window. To obtain agreement between the calculated and experimental absorption coefficients at this point, it is necessary to refine the expression for the absorption coefficient by abandoning the longwave approximation in line wings. The calculation that meets this condition is performed in the framework of a diffusion model. The time between collisions of certain type giving rise to line wing absorption is estimated. © 2012 Wiley Periodicals, Inc.