  We investigated optical absorption spectra near the fundamental absorption
edge of beta-FeSi2 single crystals by transmission measurements. The phonon
structure corresponding to the emission and absorption component was clearly
observed in the low-temperature absorption spectra. Assuming exciton state in
the indirect allowed transition, we determined a phonon energy of 0.031 +-
0.004 eV. A value of 0.814 eV was obtained for the exciton transition energy at
4K.
