Dynamical test of Davydov-type solitons in acetanilide using a picosecond free-electron laser

Picosecond infrared excitation experiments on acetanilide, an {α}-helix protein analog, indicate that the anomalous 1650-cm^-1 band which appears on cooling of acetanilide crystals persists for at least several microseconds following rapid pulsed heating. The ground-state recovery time is 15±{}5 psec, consistent with a conventional mode strongly coupled to the phonon bath. We therefore suggest that the unusual temperature-dependent spectroscopy of acetanilide can be accounted for by slightly nondegenerate hydrogen atom configurations in the crystal.