Fourier transform infrared absorption spectra of structurally differen
t phases of the radical cation salt (BEDT-TTF)2I3 in the range of the
molecular vibrations of the donor are presented. The low-temperature s
pectra provide exact fingerprints of the different phases as long they
have different unit cells. Additional differences concerning the posi
tions of ethylene groups reflect themselves in the CH2-stretching vibr
ations. As a result, it could be shown that the ethylene groups of the
alpha(t)-phase and beta-phase must have a different order. Concerning
the tempering of the different phases, it is shown that at least alph
a(t)- and x(t)-(BEDT-TTF)2I3 are the same.