  We have measured optical absorption in mid-infrared spectral range on
hydrogen intercalated epitaxial graphene grown on silicon face of SiC. We have
used attenuated total reflection geometry to enhance absorption related to the
surface and SiC/graphene interface. The samples of epitaxial graphene have been
intercalated in the temperature range of 790 to 1250$^\circ$C and compared to
the reference samples of hydrogen etched SiC. We have found that although the
Si-H bonds form at as low temperatures as 790$^\circ$C, the well developed bond
order has been reached only for epitaxial graphene intercalated at temperatures
exceeding 1000$^\circ$C. We also show that the hydrogen intercalation
degradates on a time scale of few days when samples are stored in ambient air.
The optical spectroscopy shows on a formation of vinyl and silyl functional
groups on the SiC/graphene interface due to the residual atomic hydrogen left
from the intercalation process.
