Frequency Shifts in Infrared Spectra of Ethylene Clusters

Based on structure calculations of small ethene (C2H4) clusters published previously [R. Ahlrichs et al., Z. Phys. D. 15, 341, 1990], shifts and splittings of the fundamental excitation frequency of the ν7 mode are calculated for the dimer, trimer and tetramer. Using a first order perturbation approach, we find blue shifts in the order of 1-3 cm-1 which compare well with experimental findings. It is shown that the shifts are approximately independent of the cluster size and of the isomeric structure (ring-like or chainlike) of the ethene complexes