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1

Digitale Medien

Static and dynamical distortions of helium clusters (1995)

McMahon, M. A. ; Barnett, R. N. ; Whaley, K. B.

Springer

The European physical journal 98 (1995), S. 421-428

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ISSN: 1434-6036

Schlagwort(e): 36.40.+d ; 33.70.Jg ; 67.40.Yv

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract We examine the effects of impurities (“doping”) and rotational excitation on the structural and energetic properties of helium clusters. Quantum Monte Carlo (QMC) techniques are used to study ground and rotationally excited states of pure and doped clusters. We use exponentially correlated wave functions and treat the molecular impurities as rigid. Whereas pure HeN show essentially monotonic decay of density from a central maximum value, addition of impurities induces local ordering of He to an extent dependent on the impurity-He binding. Rotational excitation of HeN gives rise to extremely large centrifugal distortions. The location of impurities also appears to change upon rotational excitation. The implications of these distortions on impurity spectra are discussed for SF6HeN, and compared to recent experimental results.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01338418

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2

Digitale Medien

CARS spectroscopy of molecules and clusters in supersonic jets (1988)

Barth, H. D. ; Jackschath, C. ; Pertsch, T. ; [weitere]

Springer

Applied physics 45 (1988), S. 205-214

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ISSN: 1432-0649

Schlagwort(e): 42.65 ; 33.20.Fb ; 36.40.+d ; 34.50.Ez

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract Supersonic molecular beams of D2, CH4, NH3, and C2H4 are investigated in the expansion region employing collinear coherent anti-Stokes Raman spectroscopy (CARS). The analysis of rotationally resolved CARS spectra allows the determination of temperatures in the beam. The rotational relaxation as a function of stagnation pressure and separation from the nozzle is studied by recording theQ branch for D2 and the ν3 R andS branches for CH4. Rotational temperatures for NH3 are determined by investigating the complete ν3 band. At strong stagnation conditions broad structures arise which can be attributed to the formation of NH3 clusters. For C2H4 the ν5 band with resolved rotational structure is reported. Again, at larger distances from the nozzle, broad structures are observed. They are assigned to the ν1 and ν5 vibrations in the C2H4 cluster.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00687148

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3

Digitale Medien

Nonlinear resonances and phase transitions of two-ion Coulomb clusters in a Paul trap: Calculations without laser cooling (1994)

Vogt, A. W.

Springer

Applied physics 58 (1994), S. 57-62

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ISSN: 1432-0649

Schlagwort(e): 32.80.Pj ; 42.50.Vk ; 36.40.+d

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The mechanism responsible for transitions of laser-cooled trapped ions from an ordered “crystal” state to an irregular “cloud” state has been discussed controversially. A numeric and analytic study of the relative motion of two trapped ions without laser cooling is performed and compared with the results of previous simulations involving the laser. It turns out that the system without laser, in spite of its simplicity, already exhibits a non-monotonic dependence of crystal stability on trap parameters, which is linked to the presence of low-order nonlinear resonances.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01081714

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4

Digitale Medien

CARS diagnostics of a CO2-laser pyrolytic experiment for the production of nanosized ceramic powders (1995)

Hoesslin, M. ; Förster, J. ; Schäfer, J. H. ; [weitere]

Springer

Applied physics 61 (1995), S. 367-375

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ISSN: 1432-0649

Schlagwort(e): 36.40.+d ; 42.65.Dr

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract Spatial distributions of rotational temperatures and molecular number densities of C2H2 and H2 were measured with CARS during the production of ultrafine SiC powders in a laser pyrolytic process flame. By means of a CO2 laser, the reaction gases SiH4 and C2H2 (or alternatively C2H4) are converted into SiC and H2. From the CARS measurements temperature gradients are determined between 8.8 × 105 K/m and 1.6 × 106 K/m with corresponding heating rates of 1.8 × 106 K/s and 1.3 × 106 K/s. The CARS data also allow an estimation of the gas expansion behaviour in the reaction zone. Moreover, they show that diffusive velocity components of the hydrogen in the hot reaction zone do not exceed 0.4 m/s.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01081537

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5

Digitale Medien

The detection and recognition of underground nuclear explosions (1995)

Argo, P. ; Clark, R. A. ; Douglas, A. ; [weitere]

Springer

Surveys in geophysics 16 (1995), S. 495-532

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ISSN: 1573-0956

Schlagwort(e): Nuclear explosion detection and recognition ; Seismology ; Remote sensing ; Radioactivity ; Ionospheric effects

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract This paper reports on a joint meeting of the Royal Astronomical Society's Joint Association for Geophysics and VERTIC (the Verification Technology Information Centre) held in London in 1992. The topics presented focused on the detection and recognition of underground nuclear explosions. The objective of the meeting was to emphasize the multi-methodological approach that is important in verifying compliance with test-ban treaties. An overview of seismological monitoring was followed by a discussion of the technical and scientific aspects of a global seismic monitoring network, and in particular of the 1991 experiment to test the large-scale international exchange of seismic data between recording stations and data centres world-wide. The current capabilities of satellite remote-sensing were presented, and their use explained in terms of both the provision of information for monitoring the development of foreign nuclear testing programmes and also for providing sufficient information for the evaluation of treaty compliance. A review of radio-isotope sampling showed how the isotopic signature of both air and ground based sampling programmes can be diagnostic of the nuclear source. Finally, previously classified research on the ionospheric effects of underground nuclear explosions was presented, the generated acoustic waves disturbing the ionosphere and producing detectable changes in the reflection of radio and radar signals which have potential as a monitoring technique.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00665683

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6

Digitale Medien

The emission of neutral clusters in sputtering (1989)

Gnaser, H. ; Hofer, W. O.

Springer

Applied physics 48 (1989), S. 261-271

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ISSN: 1432-0630

Schlagwort(e): 79.20.Nc ; 36.40.+d

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract The mass, angle, and energy resolved emission of neutral clusters in sputtering was studied for a variety of metals and semiconductors. The main phenomena and results are the following: (i) Cluster emission from a series of transition metals reveals a prominent contribution of clusters to the total flux of ejected particles but there is no simple scaling of cluster intensities with the average sputtering yields. With increasing number of constituents, relative intensities of neutral clusters decrease much faster than those of secondary-ion clusters. (ii) The relative intensities of clusters emitted from amorphous and crystalline semiconductors are identical, but the energy spectra of Ge n -clusters (n = 1–4) sputtered from Ge (111) peak at a slightly higher energy (1 eV) as compared to spectra taken from amorphous Ge. The intensities of all Ge n -clusters exhibit the same dependence on emission angle; this holds for both the amorphous and crystalline Ge-sample. (iii) The flux of neutral monomers, dimers, and trimers sputtered from Cu(111), Ni(111), and Ag(111) crystals shows a pronouncedly anisotropic emission along the 〈110〉 lattice directions which is ascribed to a momentum alignment in the anisotropic part of the collision cascade. Energy spectra taken along 〈110〉 peak at higher energies than those obtained from a random emission angle.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00619396

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7

Digitale Medien

The dimer sputtering mechanism of Cu(001) at low bombarding energy (1992)

Karetta, F. ; Urbassek, H. M.

Springer

Applied physics 55 (1992), S. 364-371

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ISSN: 1432-0630

Schlagwort(e): 79.20.N ; 36.40.+d

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract The emission of dimers during bombardment of a Cu(001) surface by Cu atoms of 300 and 1000eV energy is studied. A molecular dynamics simulation method based on many-body potentials is employed. At 300eV bombarding energy, around 81% of the sputtered dimers originate from second-nearest neighbor sites. 58% of these are ejected in a collision sequence correlated by the projectile. These dimers lead to a second maximum in the kinetic energy distribution of emitted dimers at around 8eV, besides a maximum at 4eV. Only the latter is found at 1000eV bombarding energy. As in this case mostly next-neighbor surface atoms are sputtered, the specific emission mechanism found at 300eV is irrelevant. Finally, we show that the direction of the angular momentum of sputtered dimers is correlated with the original surface site of the dimers.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00324086

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8

Digitale Medien

Orientational correlations and order in A3C60 (1993)

Gelfand, M. P. ; Lu, J. P.

Springer

Applied physics 56 (1993), S. 215-217

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ISSN: 1432-0630

Schlagwort(e): 71.25.Mg ; 71.25.Rk ; 71.20.−b ; 36.40.+d

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract A tight-binding method which has been previously applied to study the effect of uncorrelated orientational disorder on conduction-band properties is extended here to the case of systems with long-range order and/or short-range correlations. The density of states and conductivity are not highly sensitive to the specific short-range correlations, so long as the system is not too close to being fully ordered. Hence the strong effects of disorder found previously appear to be robust and should play an important role in the interpretation of normal-state properties of A3C60.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00539477

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9

Digitale Medien

Calculation of the dispersion of the third-order optical nonlinearity in C60 films (1995)

Westin, E. ; Rosén, A.

Springer

Applied physics 60 (1995), S. 49-55

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ISSN: 1432-0630

Schlagwort(e): 42.65.An ; 36.40.+d ; 31.20.Sy

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Using wave functions determined from ground-state local-density calculations, we have calculated the wave-dispersed free response of the optical nonlinear polarizabilityγ (3)(−3ω;ω,ω,ω), for the C60 molecule andχ (3)(−3ω;ω,ω,ω) i.e. Third-Harmonic Generation (THG) for films using a sum-over-states approach. The influence of screening was determined by applying an external static electric field in separate selfconsistent calculations to evaluate induced dipole moments which was used to determine the static linear and nonlinear polarizabilities. The polarizabilities calculated in the static limit were used to determine an effective screening parameter which was, in turn, used together with an RPA approach to calculate screened wave-dispersed, third-order nonlinear optical properties such asγ (3)(−3ω;ω,ω,ω) andχ (3)(−3ω;ω,ω,ω). Comparing evaluated polarizabilities with experimental values we found that the non-resonant free polarizability compares well in absolute magnitude with experimental results. Inclusion of screening results in a polarizability about two orders of magnitude below the experimental values.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01577612

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10

Digitale Medien

Desorption of metal atoms with laser light of different polarization (1993)

Götz, T. ; Vollmer, M. ; Träger, F.

Springer

Applied physics 57 (1993), S. 101-104

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ISSN: 1432-0630

Schlagwort(e): 73.20.Mf ; 82.65.Pa ; 82.50.−m ; 36.40.+d

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Laser-induced desorption of metal atoms from the surface of small metal particles has been investigated as a function of the shape of the particles and the polarization of the incident laser light. The particles were supported on LiF, quartz or sapphire substrates. In a first set of experiments, the shape of the particles was determined by recording optical transmission spectra with s- and p-polarized light incident under an angle of typically 40° with respect to the surface normal. The metal particles turn out to be oblate, the ratio of the axes perpendicular and parallel to the substrate surface being on the order of 0.5. This ratio decreases with increasing particle size. Also, the particles change shape if the temperature is raised. In further experiments, s- and p-polarized light has been used to stimulate desorption of atoms via surface plasmon excitation. It is found that the desorption rate markedly depends on the polarization of the light. This is explained by excitation of the collective electron oscillation along different axes of the non-spherical particles.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00331225

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