We have investigated vibrational effects on the cross sections for rotation
al transitions within the vibrational ground states of H-2 and HD, induced
by collisions with H atoms. We find that the shift of the mean intramolecul
ar distance from the position of the potential minimum is significant in th
e case of H scattering on H-2, where the interaction potential is only very
weakly anisotropic at low collision energies.