Excited-state dynamics of rare-gas clusters

Abstract

In this paper we explore the dynamic implications of energy exchange in electronically vibrationally excited states of mixed rare-gas clusters. The classical molecular dynamics method was applied for the study of vibrational energy flow from electronically excited atomic Xe(3P1) states in Xe*Ar12 and Xe*Ar54, and the consequences of Xe*2 (3Σu) excimer formation in Xe*2 Ar11 and Xe*2 Ar53 clusters. We have established the occurrence of an ultrafast vibrational energy flow (∼300 fs) from local Rydberg atomic and excimer excitations into the cluster, which is accompanied by large configurational dilation around the excited state, due to short-range repulsive interactions. Size effects on cluster dynamics were elucidated, being manifested by vibrational predissociation in small clusters and by vibrational relaxation and vibrational energy redistribution in large clusters. A gradual transition from reactive molecular type relaxation in small clusters to nonreactive condensed-matter type relaxation in large clusters was documented. Qualitative and quantitative differences between relaxation of excited species initially located in the interior or on the surface of the cluster were established, being exhibited in the details of the vibrational energy flow. In the case of bulk Xe*2 Ar53, excessive local heating is manifested in cluster melting, which results in mass transport of the excimer to the cluster surface. The many facets of the dynamics of electronically excited mixed rare-gas clusters are amenable to experimental interrogations.