Isotope Effects in the Spectra of Hydrogen-Bonded Complexes. Anharmonic Calculations of Isotopologues of the [F(HF)2]-Complex

The frequencies and intensities for IR absorption bands of symmetric and asymmetric hydrogen-bonded complexes [FL1FL2F](-)(L-1, L-2= K-meson Ka, proton H, deuteron D, and triton T) are calculated. The equilibrium configuration and the potential energy and dipole moment surfaces of [FL1FL2F](-)isotopologues were calculated by the MP2/6-311++G(3df,3pd) method with the basis set superposition error taken into account. The calculations of spectral parameters with allowance for anharmonic interactions of all vibrations were carried out using the second-order vibrational perturbation theory. Variation of L(1)and L(2)masses over wide limits led to significant changes in the forms of normal vibrations and anharmonic interaction constants upon isotopic substitution. The trends in the changes of spectral parameters were determined both upon transition from one symmetric isotopologue to another and upon transition from symmetric to asymmetric isotopologues. The frequency of the D-F stretching band of [FHFDF](-)was predicted in good agreement with experimental information, and the assignment of this band was improved.