A perturbation theoretical method for determination of the dependence of the intramolecular X-H(D) potential on the hydrogen bond strength

A perturbation theoretical method is proposed that allows determination of the function describing the dependence of the intramolecular XH(D) potentia l on the hydrogen bond strength. Treating the XH(D) oscillators as mixed cu bic-quartic oscillators in which the stretch-stretch couplings of the nu(X- H(D)) mode with the internal modes of the radical X may be neglected, and i ntroducing the hydrogen bonding influence through the changes in the harmon ic diagonal force constants (as proposed by Sceats and Rice [41]), it is po ssible to extract the analytical form of the function k(rr)=f(R-X ...Y) fro m the experimental <(nu)over tilde>(XH(D)) versus R-X ...Y correlations. Th e other parameters obtained by the empirical correlations, within this mode l, also have an exact physical meaning. The method is applicable to weak hy drogen bonds as well as to hydrogen bonds of intermediate strength, and, st rictly speaking, to linear X-H(D) ... Y systems. However, extension to arbi trary geometry may be easily done.