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Partial Wave Cross Sections for Collisions between Helium Atoms and Hydrogen Halide Molecules
YU Chun-Ri,CHENG Xin-Lu,YANG Xiang-Dong,

中国物理快报 , 2007,
Abstract: The close-coupling method is utilized to calculate partial cross sections for elastic and inelastic scattering of He atoms with HX (X=F, Cl, Br) molecule based on the CCSD (T) potential energy surfaces obtained in the previous research. The calculation is performed at the incident energy of 200meV. The rationality of our results has been confirmed by comparison with the available theoretical results. The tendency of the elastic and inelastic rotational excitation partial wave cross sections varying with the reduced mass of the three systems is obtained.
Allowed and forbidden transitions in artificial hydrogen and helium atoms  [PDF]
Toshimasa Fujisawa,David Guy Austing,Yasuhiro Tokura,Yoshiro Hirayama,Seigo Tarucha
Physics , 2002, DOI: 10.1038/nature00976
Abstract: The strength of radiative transitions in atoms is governed by selection rules. Spectroscopic studies of allowed transitions in hydrogen and helium provided crucial evidence for the Bohr's model of an atom. Forbidden transitions, which are actually allowed by higher-order processes or other mechanisms, indicate how well the quantum numbers describe the system. We apply these tests to the quantum states in semiconductor quantum dots (QDs), which are regarded as artificial atoms. Electrons in a QD occupy quantized states in the same manner as electrons in real atoms. However, unlike real atoms, the confinement potential of the QD is anisotropic, and the electrons can easily couple with phonons of the material. Understanding the selection rules for such QDs is an important issue for the manipulation of quantum states. Here we investigate allowed and forbidden transitions for phonon emission in one- and two-electron QDs (artificial hydrogen and helium atoms) by electrical pump-and-probe experiments, and find that the total spin is an excellent quantum number in artificial atoms. This is attractive for potential applications to spin based information storage.
Hydrogen and Helium atoms in strong magnetic fields  [PDF]
Anand Thirumalai,Jeremy S. Heyl
Physics , 2008, DOI: 10.1103/PhysRevA.79.012514
Abstract: The energy levels of hydrogen and helium atoms in strong magnetic fields are calculated in this study. The current work contains estimates of the binding energies of the first few low-lying states of these systems that are improvements upon previous estimates. The methodology involves computing the eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock partial differential equations for these one- and two-electron systems in a self-consistent manner. The method described herein is applicable to calculations of atomic structure in magnetic fields of arbitrary strength as it exploits the natural symmetries of the problem without assumptions of any basis functions for expressing the wave functions of the electrons or the commonly employed adiabatic approximation. The method is found to be readily extendable to systems with more than two electrons.
Properties of Dense Fluid Hydrogen and Helium in Giant Gas Planets  [PDF]
Jan Vorberger,Isaac Tamblyn,Stanimir A. Bonev,Burkhard Militzer
Physics , 2007, DOI: 10.1002/ctpp.200710050
Abstract: Equilibrium properties of hydrogen-helium mixtures under thermodynamic conditions found in the interior of giant gas planets are studied by means of density functional theory molecular dynamics simulations. Special emphasis is placed on the molecular-to-atomic transition in the fluid phase of hydrogen in the presence of helium. Helium has a substantial influence on the stability of hydrogen molecules. The molecular bond is strengthened and its length is shortened as a result of the increased localization of the electron charge around the helium atoms, which leads to more stable hydrogen molecules compared to pure hydrogen for the same thermodynamic conditions. The {\it ab initio} treatment of the mixture enables us to investigate the structure of the liquid and to discuss hydrogen-hydrogen, helium-helium, and hydrogen-helium correlations on the basis of pair correlation functions.
Pinning of quantized vortices in helium drop by dopant atoms and molecules  [PDF]
Franco Dalfovo,Ricardo Mayol,Marti Pi,Manuel Barranco
Physics , 2000, DOI: 10.1103/PhysRevLett.85.1028
Abstract: Using a density functional method, we investigate the properties of liquid 4He droplets doped with atoms (Ne and Xe) and molecules (SF_6 and HCN). We consider the case of droplets having a quantized vortex pinned to the dopant. A liquid drop formula is proposed that accurately describes the total energy of the complex and allows one to extrapolate the density functional results to large N. For a given impurity, we find that the formation of a dopant+vortex+4He_N complex is energetically favored below a critical size N_cr. Our result support the possibility to observe quantized vortices in helium droplets by means of spectroscopic techniques.
Atoms and Molecules in Intense Laser Fields: Gauge Invariance of Theory and Models  [PDF]
André D. Bandrauk,Fran?ois Fillion-Gourdeau,Emmanuel Lorin
Physics , 2013, DOI: 10.1088/0953-4075/46/15/153001
Abstract: Gauge invariance was discovered in the development of classical electromagnetism and was required when the latter was formulated in terms of the scalar and vector potentials. It is now considered to be a fundamental principle of nature, stating that different forms of these potentials yield the same physical description: they describe the same electromagnetic field as long as they are related to each other by gauge transformations. Gauge invariance can also be included into the quantum description of matter interacting with an electromagnetic field by assuming that the wave function transforms under a given local unitary transformation. The result of this procedure is a quantum theory describing the coupling of electrons, nuclei and photons. Therefore, it is a very important concept: it is used in almost every fields of physics and it has been generalized to describe electroweak and strong interactions in the standard model of particles. A review of quantum mechanical gauge invariance and general unitary transformations is presented for atoms and molecules in interaction with intense short laser pulses, spanning the perturbative to highly nonlinear nonperturbative interaction regimes. Various unitary transformations for single spinless particle Time Dependent Schr\"odinger Equations, TDSE, are shown to correspond to different time-dependent Hamiltonians and wave functions. Accuracy of approximation methods involved in solutions of TDSE's such as perturbation theory and popular numerical methods depend on gauge or representation choices which can be more convenient due to faster convergence criteria. We focus on three main representations: length and velocity gauges, in addition to the acceleration form which is not a gauge, to describe perturbative and nonperturbative radiative interactions. Numerical schemes for solving TDSE's in different representations are also discussed.
Time-of-Flight Spectroscopy of Muonic Hydrogen Atoms and Molecules  [PDF]
TRIUMF Muonic Hydrogen Collaboration,M. C. Fujiwara,A. Adamczak,J. M. Bailey,G. A. Beer,J. L. Beveridge,M. P. Faifman,T. M. Huber,P. Kammel,S. K. Kim,P. E. Knowles,A. R. Kunselman,V. E. Markushin,G. M. Marshall,G. R. Mason,F. Mulhauser,A. Olin,C. Petitjean,T. A. Porcelli,J. Zmeskal
Physics , 2001,
Abstract: Studies of muonic hydrogen atoms and molecules have been performed traditionally in bulk targets of gas, liquid or solid. At TRIUMF, Canada's meson facility, we have developed a new type of target system using multilayer thin films of solid hydrogen, which provides a beam of muonic hydrogen atoms in vacuum. Using the time-of-flight of the muonic atoms, the energy-dependent information of muonic reactions are obtained in direct manner. We discuss some unique measurements enabled by the new technique, with emphasis on processes relevant to muon catalyzed fusion.
The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules  [PDF]
Nicholas R. Hutzler,Hsin-I Lu,John M. Doyle
Physics , 2011, DOI: 10.1021/cr200362u
Abstract: Beams of atoms and molecules are stalwart tools for spectroscopy and studies of collisional processes. The supersonic expansion technique can create cold beams of many species of atoms and molecules. However, the resulting beam is typically moving at a speed of 300-600 m/s in the lab frame, and for a large class of species has insufficient flux (i.e. brightness) for important applications. In contrast, buffer gas beams can be a superior method in many cases, producing cold and relatively slow molecules in the lab frame with high brightness and great versatility. There are basic differences between supersonic and buffer gas cooled beams regarding particular technological advantages and constraints. At present, it is clear that not all of the possible variations on the buffer gas method have been studied. In this review, we will present a survey of the current state of the art in buffer gas beams, and explore some of the possible future directions that these new methods might take.
Ultracold hydrogen atoms: a versatile coolant to produce ultracold molecules  [PDF]
Maykel L. Gonzalez-Martinez,Jeremy M. Hutson
Physics , 2013, DOI: 10.1103/PhysRevLett.111.203004
Abstract: We show theoretically that ultracold hydrogen atoms have very favorable properties for sympathetic cooling of molecules to microkelvin temperatures. We calculate the potential energy surfaces for spin-polarized interactions of H atoms with the prototype molecules NH(triplet-Sigma-) and OH(doublet-Pi) and show that they are shallow (50 to 80 cm-1) and only weakly anisotropic. We carry out quantum collision calculations on H+NH and H+OH and show that the ratio of elastic to inelastic cross sections is high enough to allow sympathetic cooling from temperatures well over 1 K for NH and around 250 mK for OH.
Accurate determination of the scattering length of metastable Helium atoms using dark resonances between atoms and exotic molecules  [PDF]
S. Moal,M. Portier,J. Kim,J. Dugué,U. D. Rapol,M. Leduc,C. Cohen-Tannoudji
Physics , 2005, DOI: 10.1103/PhysRevLett.96.023203
Abstract: We present a new measurement of the s-wave scattering length a of spin-polarized helium atoms in the 2^3S_1 metastable state. Using two-photon photoassociation spectroscopy and dark resonances we measure the energy E_{v=14}= -91.35 +/- 0.06 MHz of the least bound state v=14 in the interaction potential of the two atoms. We deduce a value of a = 7.512 +/- 0.005 nm, which is at least one hundred times more precise than the best previous determinations and is in disagreement with some of them. This experiment also demonstrates the possibility to create exotic molecules binding two metastable atoms with a lifetime of the order of 1 microsecond.
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