Correlation has been observed between the experimentally determined harmonic frequencies, omega, and anharmonicity coefficients. X, of OH bond stretching vibrations in alkali halide, oxide, and hydrate crystals. It has been shown that simple second-order perturbation approximation formulas of omega and X can explain the omega-X correlation, and they can be used to obtain the shape of the stretching potential and an estimate of the equilibrium length of an OH bond in crystalline environment. (C) 2002 Elsevier Science B.V. All rights reserved.