A theoretical study of the infrared absorption spectra of large water clusters

Abstract

We report the results of a molecular-dynamics study of a few large water clusters, in particular (H₂O)₂₀, whose infrared spectra are of interest in connection with atmospheric absorption phenomena. The molecules are assumed to be rigid and to interact with the MCY pair potential according to classical mechanics. The velocity and dipole autocorrelation functions are obtained by computer simulation at various temperatures and the corresponding power spectra computed as functions of frequency. The results show that the clusters undergo some kind of transition (melting) around 200 K, and that dramatic changes occur in the absorption spectra between 0 K and room temperatures. It is concluded that the results obtained so far support the idea that the observed anomalous absorption of far-infrared radiation by the atmosphere could be due to large ‘liquid’ water clusters.