  The reorientation of one small paramagnetic molecule (spin probe) in glassy
polystyrene (PS) is studied by high-field Electron Spin Resonance spectroscopy
at two different Larmor frequencies (190 and 285 GHz). The exponential
distribution of the energy-barriers for the rotational motion of the spin probe
is unambigously evidenced at both 240K and 270K. The same shape for the
distribution of the energy-barriers of PS was evidenced by the master curves
provided by previous mechanical and light scattering studies. The breadth of
the energy-barriers distribution of the spin probe is in the range of the
estimates of the breadth of the PS energy-barriers distribution. The evidence
that the deep structure of the energy landscape of PS exhibits the exponential
shape of the energy-barriers distribution agrees with results from
extreme-value statistics and the trap model by Bouchaud and coworkers.
