Cover Picture: Intramolecular Dimers: A New Design Strategy for Fluorescence‐Quenched Probes (Chem. Eur. J. 15/2003)

The cover picture shows a 96‐well plate illuminated by a UV lamp and viewed through a cutoff filter. All wells contain a Cy3.5‐BHQ1 (reporter quencher) dual‐labeled oligonucleotide probe in buffer. Complementary sequence was added to three columns. The probe is virtually nonfluorescent due to static quenching through formation of an intramolecular dimer. Addition of complement separates the dye and quencher, causing fluorescence. Intramolecular dimers as a new design strategy for fluorescence‐quenched probes is discussed by M. K. Johansson and R. M. Cook in the Concepts article on p. 3466 ff.     

Effect of the initial phase of the field in ionization by ultrashort laser pulses

We report on observable new features related to ionization of atoms by laser pulses of only few cycles and some intensity. We show that for particular photo-electron energies, the angular distribution becomes asymmetric and that this asymmetry is related to the initial phase of the field. Received: 4 November 1997/Revised: 21 January 1998/Accepted: 23 February 1998     

多体相互作用对高压固氦状态方程的影响

采用量子化学自洽场方法及原子团簇理论对固氦晶格原子势能进行多体展开，定量确定了最近邻原子间距R在0.26—0.175nm之间，短程的两体到五体相互作用对晶体结合能及压缩特性的贡献，并对不同间距下多体展开式的截断位置进行了讨论. 结果表明：当最近邻原子间距R在0.26—0.175 nm之间取值，在具有hcp相结构的晶格中，氦原子势能的多体展开式是一收敛的交错型级数，该级数中两体项、四体项为正值，而三体项、五体项为负值. 当R在0.26—0.23 nm之间取值时, 仅保留级数中两体和三体项就能很好地描述晶格原子势能；当R在0.23—0.20 nm之间取值，多体展式需要展开到四体相互作用项；当R在0.20—0.175 nm之间取值必须再加入五体项贡献. 考虑到五体相互作用后，理论计算已能圆满地解释目前固氦等温压缩数据，其最大压力达 60GPa. 关键词： 固氦 状态方程 多体相互作用     

PROPAGATION OF SURFACE ACOUSTIC WAVES IN PRESTRESSED ANISOTROPIC LAYERED PIEZOELECTRIC STRUCTURES

The propagation of surface acoustic waves in layered piezoelectric structures withinitial stresses is investigated.The phase velocity equations are obtained for electrically free andshorted cases,respectively.Effects of the initial stresses on the phase velocity and the electrome-chanical coupling coefficient for the fundamental mode of the layered piezoelectric structures arediscussed.Numerical results for the c-axis oriented fihn of LiNbO_3 on a sapphire substrate aregiven.It is found that the fractional change in phase velocity is a linear function with the ini-tial stresses,and the electromechanical coupling factor increases with an increase of the absolutevalues of the compressive initial stresses.The results are useful for the design of surface acousticwave devices.     

Probing physics at extreme energies with cosmic ultra-high energy radiation

The highest energy cosmic rays observed possess macroscopic energies and their origin is likely to be associated with the most energetic processes in the universe. Their existence triggered a flurry of theoretical explanations ranging from conventional shock acceleration to particle physics beyond the standard model (SM) and processes taking place at the earliest moments of our universe. Furthermore, many new experimental activities promise a strong increase of statistics at the highest energies and a combination with γ-ray and neutrino astrophysics will put strong constraints on these theoretical models. We give an overview over this quickly evolving research field with focus on testing new particle physics.     

Photodissociation Spectroscopy and Dynamics of Weakly Bonded Metal Ion—Ethylene Complexes

The photodissociation spectroscopy of weakly bonded bimolecular complexes can give important insight into fundamental molecular interactions and dynamics. We have applied these techniques to a study of metal ion‐ethylene interactions in the Mg⁺(3s)‐C₂H₄ and Al⁺(3s²)‐C₂H₄ π‐bonded complexes. Experimental work is supported by ab‐initio electronic structure calculations. These experiments allow us to explore and compare the chemical binding, electronic structure, and nonadiabatic dissociation dynamics of these complexes.     

Advanced adiabatic approximation for momentum distributions of ejected electrons in slow atomic collisions

The problem of determination of momentum distributions of ejected electrons in slow atomic collisions is studied within the impact-parameter method by using a dynamic adiabatic basis which takes into account the correct boundary conditions. An expression is obtained which relates the momentum distribution of the ejected electrons with a coherent sum of the delocalized dynamic adiabatic eigenstates (elementary wavepackets). The form of the momentum distribution exactly coincides with the form of the total wavepacket in configuration space. General formulas are applied to a model problem of electron detachment in the process in which the electron-atom interactions are described by the zero-range potentials. In the example considered, the momentum distribution of ejected electrons, in the center-of-mass frame, exhibits a maximum located in the scattering plane on the circle of radius (in atomic units), where v is the relative collision velocity and is the impact parameter. Received: 5 October 1998