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Center for Nonlinear Studies |
Extensive configurational rearrangement following absorption of light are operative in a large class of many-body systems such as biological molecules, condensed phase chemical media and in solids such as insulators and semiconductors. Pure and doped rare gas media have long been recognized as model systems for describing and understanding the basic principles behind configurational rearrangements. Their simple structural properties and the good knowledge of their physical and thermodynamic properties make them more easily amenable to modelization. Molecular-dynamics simulations of structural relaxation in electronically excited NO-doped solid neon, argon and krypton are presented. Molecular dynamics simulations are developed using some potential interactions: Fitting potentials and Potential Energies Surfaces (PES) obtained using ab-initio quantum techniques, for the NeNO, ArNO, and H2-NO systems. The NO is excited to its lowest Rydberg state, inducing a rearrangement of the surrounding medium in the form of a bubble, due to repulsion between the Rydberg electron and the closed-shells surrounding species. The simulations were carried out using the thermal harmonic quantum correction in order to account for quantum effects. We studied the influence of the two different effective temperatures used. The first shell response is characterized by a collective oscillatory response, which point to coherent dynamics and confirm for the neon matrix, the experimentally observed slower dynamics than in solid argon and krypton. Furthermore, the medium response is characterized by a collective oscillatory behavior of the shells around impurity. The results show a behavior characterized by an impulsive expansion of the cage radius at short time (250 ps), followed by multimodal oscillations over several picoseconds. This time evolution of the average cage radius reveals an impulsive cage expansion followed by a cage contraction in about 500 ps. In connection with the PES used, we analyzed the isotropic and anisotropic contribution from the potentials in the dynamics behavior.
Host: Sergei Tretiak