Short communication A simple asymmetric lineshape for fitting infrared absorption spectra

Almost exclusively, lineshape functions used to model infrared (IR) absorption peaks are based on symmetric frequency distributions. However, in complex systems such as large biological macromolecules in aqueous solutions, the distribution of vibrational frequencies may in fact be asymmetric. In this communication, we show that asymmetry can be introduced to the standard symmetric Lorentzian and Gaussian lineshapes using a simple, easy to implementmethod. Our technique involves replacing the static width parameter of the symmetric profiles with a smoothly varying function that is wave number dependent. In this way, thewidth varies across the IR band resulting in an asymmetric peak. In ourmodel, the width varies sigmoidally with wave number. As a demonstration, we fit experimental spectra of adenosine 50-monophosphate (AMP). 2008 Elsevier B.V. All rights reserved.