By means of functional differentiation we have developed a general theory that allows one to perform the virial expansion of correlation functions and spectra. We have applied our results to the case of interaction-induced spectroscopy, for which the experimental determination of two-body and three-body spectra have been performed in several gaseous systems. We show that, in particular, the three-body experimental spectra are composed of three parts with different temperature behaviors, which allows in principle their discrimination.

• Received 22 December 1988

DOI:https://doi.org/10.1103/PhysRevA.40.1116