The absorption and emission spectra of the P-3(1)-S-1(0) transition of a Hg atom embedded in solid argon have been simulated using the molecular dynamics with quantum transitions algorithm to consider the nonadiabatic transitions between the three adiabatic states. The simulations also take into account the zero-point fluctuations at the experimental temperature of 4 K using a temperature correction that mimics them. The simulated spectra show fair agreement with the experimental data for the absolute energies and very good agreement for the absorption-emission Stokes shift. The absorption band consists of the contribution due to absorption of the three degenerate atomic states. The simulations of the emission spectrum, with inclusion of nonadiabatic couplings, lead to a single emission band stemming from the lowest adiabatic surface. When running the simulations without consideration of the nonadiabatic coupling, the simulated absorption and emission spectra exhibit three bands separated by hundreds of cm(-1), in total disagreement with the experiment. This shows that photoexcitation of Hg(P-3(1)) in Ar matrixes is characterized by the medium-induced nonadiabatic couplings among its adiabatic states.