Anharmonic corrections to structural experiment data

Anharmonic corrections to internuclear distances observed in diffraction an d microwave experiments are calculated at the level of first-order perturba tion theory. The results obtained for a simple system with the use of a qua ntum-mechanical potential function are compared with the values calculated according to currently used approximations. It is shown that the diatomic a pproximation enormously exaggerates anharmonic corrections to distances bet ween nonhydrogen atoms.