Interface Excitons in Krmnen Clusters : The Role of Electron Affinity in the Formation of Electronic Structure

The formation of the electronic structure of small Kr_m clusters (m<150) embedded inside Ne_N clusters (1200<N<7500) has been investigated with the help of fluorescence excitation spectroscopy using synchrotron radiation. Electronically excited states, assigned to excitons at the Ne/Kr interface, 1i and 1'i were observed. The absorption bands, which are related to the lowest spin-orbit split atomic Kr 3P1 and 1P1 states, initially appear and shift towards lower energy when the krypton cluster size m increases. The characteristic bulk 1t and 1't excitons appear in the spectra, when the cluster radius exceeds some critical value, R_cl>Delta_1i . Kr clusters comprising up to 70 atoms do not exhibit bulk absorption bands. We suggest that this is due to the penetration of the interface excitons into the Kr_m cluster volume, because of the negative electron affinity of surrounding Ne atoms. From the energy shift of the interface absorption bands with cluster size an unexpectedly large penetration depth of delta_1i =7.0+/-0.1 A is estimated, which can be explained by the interplay between the electron affinities of the guest and the host cluster

Excitation and radiative decay of neutral and ionic ArN clusters studied by fluorescence spectroscopy

Excitation and decay processes of neutral and ionized ArN clusters are analysed using fluorescence spectroscopy with synchrotron radiation. The fluorescence yield of ionized ArN clusters is resonantly enhanced after excitation from states related to the atomic 3s levels

Electronic excitations in liquid helium: The evolution from small clusters to large droplets

The absorption coefficient of liquid He droplets is reported in the energy range from the first electronic excitation up to the ionization limit. It is obtained from total fluorescence yield curves. The size of He droplets is varied between approximately 10$^6$ atoms/particle to small clusters containing on the order of 50 atoms. The character of the excited states is discussed in view of different theoretical approaches, i.e., molecular excitations, Frenkel and Wannier type excitons. It turned out that the Frenkel and Wannier model being very successful for the description of excited states in insulators has severe shortcomings in the case of liquid He. Furthermore, the implications for the structural peculiarities of liquid He are addressed

Electronic excitation, decay and photochemical processes in rare gas clusters

An overview of processes of electronic excitation and the subsequent following decay in clusters is presented. Pure rare gas clusters (Xe-Ne) are chosen as model systems for non-metallic clusters. Selective photo-excitation with synchrotron radiation offers the possibility to study a variety of different decay and relaxation processes (exciton trapping, desorption of electronically excited species) depending both on the cluster size and of the excitation energy. Special emphasis is given to the role of energy transfer, and in particular, vibrational energy flow, radiative and non-radiative electronic relaxation. Some recent results on the decay processes in He clusters are given in the last part of the article. Decay processes in He clusters differ remarkably from that observed in the heavier rare gas clusters

Excitation and decay processes in helium clusters studied by fluorescence spectroscopy

Excitation and decay processes of helium clusters are investigated with fluorescence methods. The results differ remarkably from that obtained for the heavier rare gas clusters. They are discussed in view of the unusual structural and electronic properties of helium

Electronic excitation, decay and photochemical processes in rare gas clusters

An overview of processes of electronic excitation and the subsequent following decay in clusters is presented. Pure rare gas clusters (Xe-Ne) are chosen as model systems for non-metallic clusters. Selective photo-excitation with synchrotron radiation offers the possibility to study a variety of different decay and relaxation processes (exciton trapping, desorption of electronically excited species) depending both on the cluster size and of the excitation energy. Special emphasis is given to the role of energy transfer, and in particular, vibrational energy flow, radiative and non-radiative electronic relaxation. Some recent results on the decay processes in He clusters are given in the last part of the article. Decay processes in He clusters differ remarkably from that observed in the heavier rare gas clusters