Rare gas ion clusters

The broken bonds (boldface=dissociated fragment) BDEs (boldface = recommended data reference in parentheses) Methods (reference in  

Note The BDE data with rare gas atom are also arranged in Chapter 11 through Chapter 27. 

---

As an application of the above program, we present some recent results [6] for rare-gas ionic clusters, which are of current interest [7-13]. The simplest DIM model is obtained by admitting only one electronic state for each atomic centre neutral atoms are assumed to be in the Sg state and the positive ions are assumed to be in the state. The positive charge is allowed to reside on any of the centres so that there are N state-groups possible for a singly ionized N-atom cluster (Rg stands for rare gas) ... 

The fonnation of clusters in the gas phase involves condensation of the vapour of the constituents, with the exception of the electrospray source [6], where ion-solvent clusters are produced directly from a liquid solution. For rare gas or molecular clusters, supersonic beams are used to initiate cluster fonnation. For nonvolatile materials, the vapours can be produced in one of several ways including laser vaporization, thennal evaporation and sputtering. 

Considerable effort has been expended on Ag atoms and small, silver clusters. Bates and Gruen (10) studied the spectra of sputtered silver atoms (a metal target was bombarded with a beam of 2-keV, argon ions produced with a sputter ion-gun) isolated in D, Ne, and N2. They found that an inverse relationship between Zett of the metal atom and the polarizability of rare-gas matrices (as determined from examination of... 

Elucidating the origin of magic numbers has been a problem of long-standing interest, made accessible through the use of the laser-based reflectron TOF technique and evaporative ensemble theory. Three test cases are considered, first protonated ammonia clusters where (NH3)4 NHj has been found to be especially prominent, and then two other cases are considered, one involving water cluster ions and another rare gas clusters. 

The relativistic coupled cluster method starts from the four-component solutions of the Drrac-Fock or Dirac-Fock-Breit equations, and correlates them by the coupled-cluster approach. The Fock-space coupled-cluster method yields atomic transition energies in good agreement (usually better than 0.1 eV) with known experimental values. This is demonstrated here by the electron affinities of group-13 atoms. Properties of superheavy atoms which are not known experimentally can be predicted. Here we show that the rare gas eka-radon (element 118) will have a positive electron affinity. One-, two-, and four-components methods are described and applied to several states of CdH and its ions. Methods for calculating properties other than energy are discussed, and the electric field gradients of Cl, Br, and I, required to extract nuclear quadrupoles from experimental data, are calculated. 

The result of intensity alternation for the boron nitride cluster ions is in accordance with the generation of high cluster ion beams MnXn, for several systems (e.g. NaCl, CuBr or Csl26 49) by other methods of cluster formation such as by quenching condensation in a cold rare gas or by ion bombardment of hahdes. 

Dehmer and Pratt were one of the earliest groups to observe resonance structures in the photoionization efficiency (PIE) curves of small argon ions and mixed rare gas cluster ions (Dehmer and Pratt 1982 Pratt and Dehmer 1982). The structures in the PIE curves of small argon cluster ions were attributed to interband transitions while the features observed in the PIE curves of mixed rare gas cluster ions were suggested to arise from autoionizing states. Walters et al. (1985) also observed similar resonances in the PIE curves of C6H6/HC1... 

Evidence that clustering of rare gas atoms occurs around ions comes from (a) ion mobility measurements, and (b) volume changes occurring on electron attachment to solutes. The mobility of positive ions in xenon decreases with increasing pressure and at pressures near 100 bar is 1.3 X 10 cm /Vs [see Fig. 3(a)] near room temperature. An estimate of the size of the cluster moving with the ion may be obtained from such data using the Stokes equation. 

Several distinct energy loss peaks appear within the MgO band gap (between 1 and 5.5eV energy loss [218]) as a function of cluster size. These loss peaks cannot be assigned to low-lying transitions in the atom or in the ion [103,208,219,220]. EEL spectra of vapor deposited Ag, which forms islands and thin films via surface diffusion at sample temperatures between T = 100 and 500 K, have shown losses at 3.8 and 3.2 eV attributed to an Ag surface plasmon and to an Ag-MgO interface plasmon, respectively [218]. In contrast, the EEL spectra shown in Fig. 1.44 and recorded at T = 45K exhibit clearly a size dependence, which reflects the change in the electronic structure of the clusters. A similar behavior has been observed in optical absorption spectra of Ag (n < 21) clusters deposited in rare gas matrices [221], which has been interpreted as a manifestation of collective excitations (Mie plasmons) of the s electrons influenced by the ellipsoidal shape of the clusters. Some similarities but also some differences in the general trend with cluster size have been observed by comparing the optical absorption data shown in [221] with these EELS data [214]. In this context, it is important to note that EELS probes... 

---