Electronic excitation and thermal effects in alkali-halide cluster anions

We have observed electronically excited states in alkali-halide cluster anions with one excess electron. Using photoelectron spectroscopy, we have found two narrow states in (KI)-2, (NaI)-2, and (NaCl)-2, consistent with a dipole-bound electron, while larger cluster anions exhibit a single broad excited state. In the larger systems, electronic excitation is often accompanied by vibrational excitation and thus a change in cluster temperature. Such temperature changes affect cluster structure and in some cases lead to rapid thermal isomerization.     

Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems

We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein--Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals.     

Electronic excitation migration in neodymium pentaphosphate

A direct measurement of the diffusion distance of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ state excitation in NdP₅O₁₄ along the crystallographic a-axis is reported. At room temperature an upper limit of 32 nm is found which is 20 times shorter than an earlier estimate.     

Electronic and rotational excitation of H2 by positron impact

The body frame fixed nuclei and the laboratory frame rotational close coupling approximations have been employed to calculate electronic excitation of H₂ (X¹ _g ⁺ B¹ _u ⁺ ) by positron impact. Two electronic states (X¹ _g ⁺ and B¹ _u ⁺ ) and three rotational states in both the elastic and excitation channels are retained in the calculations. Results are reported for electronically elastic, excitation and rotational cross sections up to the incident energy 75.0 eV. The elastic cross sections are found to be influenced significantly with the addition of B¹ _u ⁺ state in the expansion scheme, in both the models used. Above the incident energy of 25.0 eV, the electronic excitation cross sections using the laboratory frame differ significantly from those of the fixed nuclei model.     

Electronic excitation energy transfer in poly-N-epoxypropyl-3,6-dibromocarbazole

Physics of the Solid State - The mechanisms of electronic excitation energy transfer in films of poly-N-epoxypropyl-3,6-dibromocarbazole doped with pyrene, rubrene, and...     

Electronic excitation processes in rare gas clusters studied by electron energy loss spectroscopy

We present the electron energy loss spectra for Ar clusters as a function of incident electron energy and of cluster size. In spectra measured with 100 eV incident electron energy the bulk excitation peak becomes visible for a mean cluster size above 170 atoms per cluster. For 250 eV incident electron energy the bulk excitation peak is clearly observable even for a mean cluster size of 120 atoms per cluster. These experimental results are qualitatively reproduced by a simple calculation that accounts for the mean free path of electrons in Ar clusters; i.e., the penetration depth of incident electrons into the cluster.     

Electronic excitation dynamics and energy transfer in lithium-gadolinium borates doped by rare earths

This paper reports on luminescence studies of lithium borate Li₆Gd(BO₃)₃ doped with Eu³⁺ and Ce³⁺ and Li₆Eu(BO₃)₃ crystals upon selective excitation by synchronous radiation in the pump energy region 3.7–27 eV at temperatures of 10 and 290 K. The effective energy transfer between the rare-earth ions Gd³⁺ → Ce³⁺ and Gd³⁺ → Eu³⁺ is found to operate by the resonant mechanism, as well as through electron-hole recombination. A study is made of the fast decay kinetics of the Ce³⁺-center activator luminescence under intracenter photoexcitation and excitation in the interband transition region. The mechanisms underlying luminescence excitation and radiative relaxation of electron states of rare-earth ions are analyzed and energy transfer processes active in these crystals are discussed.     

Electronic excitation and dynamic promotion of a surface reaction

The mechanism of recombinative desorption of hydrogen from a Ru(0001) surface induced by femtosecond-laser excitation has been investigated and compared to thermally initiated desorption. For the laser-driven process, it is shown that hot substrate electrons mediate the reaction within a few hundred femtoseconds resulting in a huge isotope effect between H2 and D2 in the desorption yield. In mixed saturation coverages, this ratio crucially depends on the proportions of H and D. Deviations from second order desorption kinetics demonstrate that the recombination is dynamically promoted by excitation of neighboring, but nonreacting adatoms. A concentration dependent rate constant which accounts for the faster excitation of H versus D is proposed.     

Electronic excitation of ice monomers on Au(111) by scanning tunneling microscopy

Scanning tunneling microscopy, inelastic tunneling spectroscopy, and electron induced manipulation are used to investigate electronic excitation of D₂O monomers and small clusters adsorbed at the elbows of the Au(111) reconstruction. Diffusion of molecules, dissociation of clusters, and rearrangement of the reconstruction is induced by electronic excitation. Threshold energies of between 200 and 250 meV and of 446 meV are explained by combined vibrational modes of D₂O molecules. External vibrational modes of D₂O molecules on Au(111) are identified by inelastic tunneling spectroscopy at ≈18, 30, and 41 meV.     

Presence of nonlinear interference effects as a source of low frequency excitation force in vibro-acoustography

The vibro-acoustography imaging method consists of forming an image of the deformability of a tissue submitted to a low frequency fLF stress field. This sound field can be created locally by means of a focused annular array emitting two primary beams driven at two close frequencies fa and fb = fa + fLF. In the existing literature, the origin of this stress field has been identified as the low frequency radiation pressure of the two primary beams. However, this work intends to show that another contribution to this internal stress is the low frequency field distributed in the object volume and created by the nonlinear interferences of the two primary beams. This nonlinear field was calculated in the case of multiple ring annular arrays and compared with the qLF beam experimentally measured in a water tank. The agreement between the theoretical and experimental curves provides information on the possibility that this nonlinear effect takes place in vibro-acoustography.     

Global absorption center map of the mafic minerals on the Moon as viewed by CE-1 IIM data

Determining the global distribution of minerals on the Moon has been an important goal of lunar science. Hyperspectral remote sensing is an important approach to acquiring minerals on the Moon on the global scale. The wavelength of the absorption band center is the key parameter for identifying minerals with reflectance spectra as well as remote sensing data. The global absorption center map of the mafic minerals of the Moon was produced for the first time with the Chang’E-1 IIM data. This map shows the global distribution of mafic minerals such as orthopyroxenes, clinopyroxenes, and olivine and even plagioclase feldspar of the Moon. The validation for some representative areas indicates that the global map is reliable and even more detailed than the results derived from Clementine-data. Moreover, our method is insensitive to the topography and viewing and illumination geometries. The global absorption band center map not only contributes to the lunar science research, but also has other implications to be further studied. Moreover, the preprocessing methods such as calibration and correction introduced in this study can be useful in other research with IIM data.     

Final-state effects in the excitation spectra of deep impurities in semiconductors

The excitation spectra of deep impurities have usually been interpreted in terms of transitions to continuum states having the same energy distribution and Bloch-like character as the perfect-crystal band states. Here we provide theoretical analysis and experimental evidence showing that deep-level spectra may in fact be dominated by bound and quasibound final states induced by the strong short-range impurity potentials.     

Spin chains viewed as the fermionic parts of supersymmetric quantum mechanical models

This paper shows that (anisotropic) spin chains of XY type arise by matrix representation of the fermionic terms of hamiltonians of quantum systems whose supersymmetry involves in general no more than a single hermitian supercharge. It provides some background relevant to this type of supersymmetry and makes applications to such chains including those which admit quantum groups as invariance algebras.