The results of DFT calculations of harmonic and anharmonic frequencies of the dihydrogen bonded (DHB) complexes H3EH-⋯HOR (E = B, Al, Ga and HOR = CH3OH, CF3CH2OH) in gas phase and in low polar medium (by CPCM model) in comparison with the partners are presented. Normal coordinate analysis of the low-frequency modes was carried out to assign the new vibrations induced by DHB formation by the potential energy distribution values. Among them, the intermolecular H⋯H stretching vibrations only have individual modes. The influence of central atom mass and isotope and the strength of the proton donor effects were determined. The systems convenient for IR studies were chosen from the calculation predictions. The spectral investigation was made on the BH4-/ROH complexes (ROH = CH2FCH2OH (MFE), CF3CH 2OH (TFE), (CF3)2CHOH (HFIP)). The results of temperature dependence, isotope substitution, and influence of the protondonor strength studies agree with the theoretical conclusions. Combination of experimental and theoretical approaches allowed determining for the first time the intermolecular stretching mode characterizing intrinsic DHB vibrations. © 2008 American Chemical Society.