The complete vibrational spectra assignment of dihydrocoumarin is performed through a combined vibrational spectroscopy and DFT calculations approach. To provide effective information, vibrational analysis was also performed for alpha-pyrone and coumarin related systems. The presence of extra components in the vC=O band profile can only be understood by both Fermi resonance and monomer/dimer equilibrium phenomena, the latter established by C-H center dot center dot center dot O hydrogen bond with Delta H degrees value of -8.4 +/- 0.9 kJmol(-1). The analysis of the vC-H region indicates that both the methylene and aromatic C-H groups have a significant contribution to the formation of C-H center dot center dot center dot O bonded dimers in liquid dihydrocoumarin. (C) 2012 Elsevier B.V. All rights reserved.