  The radiation transport problem in the plane-parallel medium with the large
velocity gradient is considered. The Sobolev approximation is used. The effects
of continuum absorption and line overlap are taken into account. The photon
loss probability functions are calculated and tabulated. Two calculations are
performed - for the Gaussian spectral line profile and for the rectangular
profile. It is shown that at particular choice of the rectangular profile width
the results of the calculations are very close. The evaluated photon loss
probability functions may be used in the calculations of energy level
populations of OH molecule in the interstellar gas flows.
