Krypton clusters

Table 1. Average cluster-size N) of krypton clusters for typical experimental expansion conditions using a nozzle diameter of 50 fan. The correlation of r with (N) is obtained from Ref. 63.

Various experimental approaches have been used in the past to correlate r with (N). These include electron diffraction, mass spectrometry, and molecular beam scattering experiments. The latter approach is especially suitable for the low ( )-regime. The typical value range that is available for core level excitation on krypton clusters in our experiment is (N) < 1700, if the correlation of Farges et al. is used. Somewhat lower values are obtained, if the more recent, but likely more realistic calibration of Karnbach et cd. is applied (cf. Table 1). ... 

Figure 3 shows a mass spectrum of krypton clusters. Neutral clusters are grown by expansion of the gas through a nozzle into vacuum. Several abundance anomalies, often called magic numbers , are observed. Two questions arise (1) Assuming the numbers indicate enhanced stability, is there a growth sequence that can consistently explain them (2) Do the anomalies exist before ionization, or are they caused by dissociation following ionization ... 

Figure 3 Mass spectmm of krypton clusters, grown in a supersonic expansion and ionized by electron impact. The cluster size and assumed cluster structure of particularly prominent mass peaks is indicated.

Nickel carbonyl radicals show an even greater tendency than cobalt carbonyls to cluster in a krypton matrix. Three binuclear nickel carbonyls have been detected by EPR spectroscopy in the products of y-irradiated Ni(CO)4 in Kr, yet no mononuclear species has been positively identified (65). 13C hyperfine structure has... 

Recent experiments by Citrin and coworkers (41) have clarified the role of the support in photoemission from small metal clusters. They condensed several monolayers of krypton onto either platinum or sodium metal substrates. By varying the thickness of the krypton from one to ten monolayers, the surface could be converted from metal to semimetal to insulator. The krypton peak position provides a direct measure of the sample vacuum level (32). The krypton layers are thin, less than 10 monolayers, so that the vacuum level is determined by the metal substrate. Onto the krypton layers, sodium clusters were deposited at varying coverages. Shifts in the Kr 4s and Na 2p binding energies were recorded relative to the Fermi level of the grounded substrate. 

Computer simulation of molecular dynamics is concerned with solving numerically the simultaneous equations of motion for a few hundred atoms or molecules that interact via specified potentials. One thus obtains the coordinates and velocities of the ensemble as a function of time that describe the structure and correlations of the sample. If a model of the induced polarizabilities is adopted, the spectral lineshapes can be obtained, often with certain quantum corrections [425,426]. One primary concern is, of course, to account as accurately as possible for the pairwise interactions so that by carefully comparing the calculated with the measured band shapes, new information concerning the effects of irreducible contributions of inter-molecular potential and cluster polarizabilities can be identified eventually. Pioneering work has pointed out significant effects of irreducible long-range forces of the Axilrod-Teller triple-dipole type [10]. Very recently, on the basis of combined computer simulation and experimental CILS studies, claims have been made that irreducible three-body contributions are observable, for example, in dense krypton [221]. 

With increaang temperature an ordering process takes place in which clustering of Mo interstitials as well as of krypton atoms and at higher temperatures interactions with vacancies probably take place. 

Matrix-IR spectra of CO/N2H4 mixtures show the formation of 3 weak complexes, identified by comparison with ab initio and DFT calculations.521 The variable-temperature IR spectra (—105 — 150°C) of Me2NNH2 in liquid krypton show that only the gauche conformer is present.522 DFT calculations gave vibrational wavenumbers for (XMYH)n rings and clusters, where M = Al, Ga or In Y = N, P or As n = 1-6.523... 

Van der Waals complexes were observed between two molecules of 1,2,4,5-tetrazine (la) and helium, argon, krypton, xenon, hydrogen, water, hydrochloric acid, acetylene or benzene 28 36- 396-420 jn coi,j environment of a jet expansion. In favorable systems it has been possible to determine the ground and excited state geometry of the cluster by laser spectroscopy. From these structures, it has been found that 1,2,4,5-tetrazine possesses a number of different binding sites. Helium and argon bind to the equivalent sites above and below the ring.28-30 The predominant interaction in these clusters is presumably the attractive dispersion force. 

The solubility of inert gas atoms (such as xenon, krypton and radon) in inorganic solids is small. The inert gases are trapped at lattice defects such as vacancy clusters, grain boundaries and pores. The defects in the solids can serve both as traps and as diffusion paths for the inert gas. A survey of the influence of various factors on the migration of inert gases in solids is given in a monograph by Balek [1]. 

Modem supersonic molecular beam techniques provide a direct way to study the stability and valence electron structure of noninteracting, isolated atomic clusters. One of the most widely studied properties is the threshold for photo-ionization and its dependence on cluster size. In Fig. 4.20 we reproduce some experimental results for argon-, krypton-, xenon- (Gantefor et al., 1989), and mercury-clusters (Rademann et al.. 

S. Hirabayashi, K.M.T. Yamada, Infrared spectra and structure of water clusters trapped in argon and krypton matrices. J. Mol. Struct. 795(1-3), 78-83 (2006)... 

Figure 10 Measured and predicted (solid line) apparent metastable decay rates (metastable fraction divided by the experimental time window) for three different cluster ion sizes and two different rare gases (open symbols, argon filled symbols, krypton) versus time since electron ionization. After Ji Y, Foltin M, Liao CH and Mark TD (1992) Journal of Chemical Physics 96 3624.

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