This is a joint effort of an experimental and a theoretical group to understand neutron scattering linewidths of almost free quantum rotors. In the first part we introduce a new method for simulating the dynamics of small quantum systems at finite temperatures. Thermal fluctuations are implemented through a stochastic perturbation potential, which drives the system to thermal equilibrium. It is modeled in analogy to the classical Langevin equation. In the second part we present neutron scattering data for the NH3-rotor in Ni-Ni-2C(12)H(10) Hofmann clathrates. By comparison of the experimental with the simulated data we find a classical behavior for the coupling strength of the phonons to the rotor.