  We present the results of the ethynyl (C2H) emission line observations
towards the HII regions S255 and S257 and the molecular cloud between them.
Radial profiles of line brightness, column density, and abundance of C2H are
obtained. We show that the radial profile of the ethynyl abundance is almost
flat towards the HII regions and drops by a factor of two towards the molecular
cloud. At the same time, we find that the abundance of ethynyl is at maximum
towards the point sources in the molecular cloud -- the stars with emission
lines or emitting in X-ray. The line profiles are consistent with the
assumption that both HII regions have front and back neutral walls that move
relative to each other.
