Eur. Phys. J. D 25, 149–155 (2003) DOI: 10.1140/epjd/e2003-00239-9 T HE EUROPEAN P HYSICAL JOURNAL D Study of the structural photoinduced dynamics of a solid Kr matrix with an NO impurity J.C. Castro Palacios 1, a , L. Velazquez 1, b , G. Rojas-Lorenzo 2, c , and J. Rubayo-Soneira 2, d 1 Departamento de F´ ısica, Universidad de Pinar del R´ ıo, Mart´ ı 270, Esq. 27 de Noviembre, Pinar del R´ ıo, Cuba 2 Departamento de F´ ısica General y Matem´aticas, Instituto Superior de Ciencias y Tecnolog´ ıa Nucleares Quinta de los Molinos, Ave. Carlos III y Luaces, Plaza C. Habana, Cuba Received 13 October 2002 / Received in final form 27 February 2003 Published online 30 July 2003 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2003 Abstract. In the present work we studied the immediate medium response to the excitation to the A(3sσ) Rydberg state of NO impurity embedded in a solid Kr matrix. The excitation, extended over a large range of the lattice was investigated by classical molecular dynamics simulations. This has been done using Lennard-Jones pair potentials from the literature for the NO(X 2 Π)-Kr interactions and fitted in this work for the NO(A 2 Σ + )-Kr ones, since these last have not been reported in literature. Thus is obtained the first shell response to the excitation of the impurity (approximately the first 2 ps) as well as the response of the continuous shells up to the 10th one. This first response of the first shell is compared to that for similar systems (Ne and Ar matrixes doped with NO). Therefore some theoretical conclusions are drawn. The results indicate the inertial character of the response propagation throughout the surrounding medium and the high degree of nuclear coherence at short times. PACS. 34.30.+h Intramolecular energy transfer; intramolecular dynamics; dynamics of van der Waals molecules – 02.70.Ns Molecular dynamics and particle methods – 31.70.Ks Molecular solids 1 Introduction The many-body dynamics in response to photoexcita- tion in condensed media is of general interest in many systems, such as: biological molecules, condensed phase chemical media and solids (insulators and semiconductors [1]). Extensive configurational rearrangements following photoabsorption are observed in such systems. Pure and doped rare gas solids have long been considered as good model systems for describing and understanding the ba- sic principles behind such a medium response [2–4]. They result amenable to modelization because of their simple structural properties and the great knowledge of their physical properties. To this respect, molecular dynamics simulations have been used to describe simple photochem- ical reactions during this decade in rare gas liquids [5–8], solids [4,7,9–12] and clusters [9,10,13,14]. Such events are driven by the photoinduced intramolecular motion which induces nuclear dynamics of the surrounding cage [11,15, 16], as well as long range propagation of energy [16–18]. a e-mail: juanc@geo.upr.edu.cu b e-mail: luisberis@geo.upr.edu.cu c e-mail: german@fctn.isctn.edu.cu d e-mail: jrs@fctn.isctn.edu.cu It is known that excitation of low-n Rydberg states of impurity molecules or atoms in rare gas solids leads to a large blue spectral shift in absorption, as compared to the gas phase, due to the strong short range repulsion be- tween the Rydberg electron and the closed shell of rare gas atoms [2,19]. The strong repulsion leads to a relaxation of the cage species surrounding the excited center to a new equilibrium configuration from which fluorescence occurs. The large absorption-emission Stokes shifts that are ob- served reveal the extensive lattice rearrangements around the excited species. The basic mechanism is considered to be a radial expansion of the cage (the so-called electronic “bubble” formation) [1,2,19,20] which is also operative in rare gas liquids and clusters [1,2,21]. In the case of rare gas van der Waals solids, cage re- laxation upon Rydberg state excitation of impurities has been intensively studied over the past few years [2, 4, 19, 20, 22–25]. Chergui et al. have mainly investigated the case of NO-doped rare gas solids [4,19,24,26] and H 2 solids [4,22,25]. However, combining molecular dynamics (MD) simu- lations and a normal mode analysis a better study can be done. Jim´ enez et al. [27,28] have developed computer simulations to study the dynamics of structural relaxation in Rydberg excited NO-doped Ar crystals. They have rea- sonably described the experimental results for the Stokes