Electronic Energy Dissipation Processes in Doped Rare Gas Clusters With a Shell-Like Structure

Abstract

Energy relaxation processes of photoexcited Ar M clusters (M < 50) covered with a shell of Kr atoms (up to 30 atoms) which are embedded in large Ne N clusters (N = 3500) are investigated with energy-resolved fluorescence spectroscopy. In the energy range of the Ne cluster absorption (16.5–18 eV) a strong energy transfer to the embedded Ar subcluster is observed, which results in desorption of electronically excited Ar * atoms. Ar * move through the Ne cluster, desorb and emit visible and near-infrared light in the vacuum ( 4p → 4s ). By coating the Ar clusters with Kr atoms, the Ar lines disappear and 5p → 5s transitions of Kr become dominant. Additionally, new bands occur, which are assigned to transitions of perturbed atomic Ar 4p states inside Ne clusters. A simple kinematic model is suggested to describe the suppression of desorption of excited Ar atoms from Ne clusters.

Cage effect for the photodissociation of H2O molecules in argon clusters embedded inside neon clusters

“…8 This process is similar to the exciton-induced desorption in pure rare gas solids. 16 In the so-called ''cavity-ejection mechanism,'' the interaction of the electronically excited atomic Ar*(4p) centers with surrounding neutral Ar atoms ͑whether it is repulsive or attractive͒ is correlated to the sign of the V 0 value ͑electron affinity͒ of the respective solid.…”

“…To surmount this limitation, we have employed a ''sequential pick-up'' technique. 8 A conical nozzle (Dϭ200 m, 2 ϭ4°͒ is the source of large clusters made out of light atoms ͑Ne in our case͒. The nozzle is mounted on a liquid helium cryostat and was operated at typical temperatures down to 30 K and stagnation pressures up to 200 mbar, which assured the creation of large Ne N clusters.…”

“…8 Using the same experimental setup, one can a priori expect in our case the formation of an atomic Ar shell around the solute H 2 O molecule. In our experiments we attempted the fixing of m Ar atoms around the H 2 O molecule by varying the argon cross-jet pressure.…”

“…The only observed excited fragment in H 2 O-doped neon clusters is OH*(A) with a very low rotational temperature of ϳ10 K, which is a characteristic temperature of neon clusters. 7 Moreover Ne N Ar m cluster experiments show that the energy transfer from a large host neon cluster to a small embedded argon cluster results principally in the Ar*(4p) atom desorption, 8 which emits in the IR spectral region. As a consequence, the competitive channel in the energy relaxation process might be the Ar*(4p) atoms desorption.…”

“…7 Using a three-beam doping technique, which consists of a sequential pick-up of H 2 O molecules in a first step and Ar atoms in a second step from two cross-jets by large Ne clusters prepared in a supersonic expansion, we were able to build a shell of up to approximately 100 Ar atoms around the H 2 O molecule. 8,9 Small cold H 2 O@Ar m clusters (mр10 2 ) were stabilized inside large Ne N clusters (NϷ7.5ϫ10 3 ). Fluorescence of the OH*(A) fragments has been studied as a function of the number of deposited Ar atoms m. As a result, the cage effect has been observed for the first time in doped rare-gas clusters with a shell-like structure.…”