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 α-pyrone and coumarin related systems. The presence of extra components in the νCdouble bondO band profile can only be understood by both Fermi resonance and monomer/dimer equilibrium phenomena, the latter established by C–H···O hydrogen bond with ΔH° value of −8.4 ± 0.9 kJ mol−1. The analysis of the νC–H region indicates that both the methylene and aromatic C–H groups have a significant contribution to the formation of C–H···O bonded dimers in liquid dihydrocoumarin.