Coherence loss for vibrational and librational excitations in solid nitrogen

We have investigated the process of phase relaxation (loss of coherence) for the Ag vibrational exciton (vibron) and the Eg libron in crystalline α-N2 at liquid helium temperatures. The relaxation of the Ag vibron was found to be a nonexponential decay whose effective decay constant (1/T2) decreases with time. In the first 100 ns of the decay, the effective decay time of the observed signal (T2/2) ranged from T2/2<1 ns to T2/2=14.5 ns. The decay is due to a statistical distribution of crystal defects; its qualitative features are in agreement with simple theories of disorder scattering in crystals. The decay of the Eg libron was found to be at least 28 times faster than that of the Ag vibron (i.e., T2/2<36 ps during the first few ns) and could not be measured directly.