The Procter & Gamble Company, West Chester, Ohio 45069, USAReceived August 3, 2011, Accepted September 15, 2011We explored the interpretation of the well-accepted correlation between the apparent peak maximum positionshift and extent of molecular interactions, like hydrogen bonding and dipole-dipole interactions, based on theoverlapped multiple band model. The simulation of two overlapped Lorentzian bands was carried out tointerpret how the maximum position of a composite peak relates to the relative contributions of two speciesrepresenting the different levels of molecular interactions, i.e., free (or very weekly bound) vs. strongly bound.To demonstrate the validity of our interpretation of the origin of the peak position shift, the temperature-dependent IR spectra of ethylene glycol were also analyzed. It was found through the analysis of simulated andexperimental spectra that the apparent peak shift in certain case can be safely interpreted as the measure of thestrength of hydrogen bonding. The result of this study gives a new insight to interpret molecular interactionsprobed by vibrational spectroscopy. Key Words : Frequency shifts, Overlapped bands, Self-modeling curve resolution (SMCR), Hydrogen bond-ing, Molecular interactionIntroductionThe extent of bathochromic shift of certain IR peaks underthe influence of temperature or solution composition hasbeen historically used as a convenient metric to characterizethe degree or strength of specific molecular interactions,such as hydrogen bonding and dipole-dipole interactions.Pimentel and Sederholm published a classical paper on the“empirical correlation” between shift of stretching fre-quencies and hydrogen bond distances in solid crystals.