Computer simulations of the Raman Q-branch of nitrogen in helium

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Abstract
Dynamical computer simulations have been performed on a single nitrogen particle in helium at room temperature and pressures ranging from 0.6 up to 8.7 GPa. Both the frequency and the linewidth have been determined. The ‘‘repulsive’’ contribution to the frequency is comparable to that in pure nitrogen. In contrast with the pure component case, the experimental values for the shift in the mixture are higher than those obtained from the simulations. From the difference between the experimentally determined shift and the simulation results, an estimate has been made of the change in interaction energy with the surrounding particles on excitation of a nitrogen molecule. A good fit is obtained by the addition of a weak Lennard‐Jones potential. The results for the linewidth reveal a marked difference to those for a system of pure N2, which has been confirmed by experimental evidence. This behavior, is for the greater part, due to a significant difference in the time correlation of the vibration frequency and the resulting correlation time.