Self-trapping of infrared energy absorbed in acetanilide

Acetanilide (ACN) has an anomalous low temperature IR absorption band, which has been attributed to a self-trapped state of molecular vibrational energy in the amide group (Davydov-like soliton). A classical model for a segment of an ACN chain has been set up, taking into account the degrees of freedom of the amide group involved in the H-bond: stretching of C=O bond, stretching and bending of the H-bond. The dynamics of the molecule has been investigated by molecular dynamics simulation.