Molecular-dynamics simulation of pressure broadening of sodium resonance line by argon

A molecular-dynamics simulation of the pressure broadening of the sodium resonance line by argon gives an absorption line shape which is compared to results from the Anderson-Talman classical path theory. The system consists of 255 argon atoms and one sodium atom in a box with periodic boundary conditions. The size of the box and the initial velocities are chosen to correspond to a particle density of 2×${10}^{21}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and a temperature of 450 K. The time-dependent difference potential matrix is utilized in an adiabatic approximation to give the molecular-dynamics line shape. Spin-orbit coupling and Doppler broadening are neglected. A Fourier-transform technique is used to evaluate the Anderson-Talman theory line shape for the same system. Remarkable agreement is found between the molecular-dynamics line shape and the line shape obtained from the one-perturber spectrum by means of the Anderson-Talman theory. Comparison of molecular-dynamics line shapes calculated with a scalar and with a vector dipole transition moment shows that relaxation of polarization has a significant broadening effect on the center of the line.