  To test basic assumptions inherent to most theories of molecular liquids and
glasses, Infrared spectroscopy is carried out on short polyalcohols at
temperatures ranging from far above to far below their glass transition. By
analyzing specific vibrations, the thermal expansion of covalent bonds and
hydrogen bridges is determined revealing striking differences. A comparison
with density verifies the negligibility of \textit{intra}molecular expansion
but exposes severe inhomogeneities on \textit{inter}molecular scale. This
signals distinct roles in glassy densification and promotes an atomistic
understanding.
