  Liquid scintillators are a common choice for neutrino physics experiments,
but their capabilities to perform background rejection by scintillation pulse
shape discrimination is generally limited in large detectors. This paper
describes a novel approach for a pulse shape based event classification
developed in the context of the Double Chooz reactor antineutrino experiment.
Unlike previous implementations, this method uses the Fourier power spectra of
the scintillation pulse shapes to obtain event-wise information. A
classification variable built from spectral information was able to achieve an
unprecedented performance, despite the lack of optimization at the detector
design level. Several examples of event classification are provided, ranging
from differentiation between the detector volumes and an efficient rejection of
instrumental light noise, to some sensitivity to the particle type, such as
stopping muons, ortho-positronium formation, alpha particles as well as
electrons and positrons. In combination with other techniques the method is
expected to allow for a versatile and more efficient background rejection in
the future, especially if detector optimization is taken into account at the
design level.
