Teck-Ghee Lee

Auburn University | AU · Department of Physics

Upon investigating whether the antineutron-nucleus annihilation cross-sections at very low momenta p satisfy Bethe-Landau's power law of σann(p)∝1/pα, we uncover unexpected regular oscillatory structures in the low antineutron energy region from 0.001 to 10 MeV, with small amplitudes and narrow periodicity in the logarithm of the antineutron energi...

Upon investigating whether the variation of the antineutron-nucleus annihilation cross-sections at very low energies satisfy Bethe-Landau's power law of $\sigma_{\rm ann} (p) \propto 1/p^{\alpha}$ behavior as a function of the antineutron momentum $p$, we uncover unexpected regular oscillatory structures in the low antineutron energy region from 0....

The synthetic emission spectra and opacity of high-density, high-temperature germanium (Z=32) plasma from super-transition-array (STA) calculations are presented. The viability of the STA model, which is based on a statistical superconfigurations accounting approach for calculating the atomic and radiative properties, is examined by comparing and c...

The synthetic emission spectra and opacity of high-density, high-temperature germanium (Z=32) plasma from super-transition-array (STA) calculations are presented. The viability of the STA model, which is based on a statistical superconfigurations accounting approach for calculating the atomic and radiative properties, is examined by comparing and c...

This thesis examines the inelastic processes of a variety of ion-atom collision systems in a wide range of collision energies. A semi-classical and fully quantum mechanical close-coupling methods were employed.

A theoretical model based on the method of super transition arrays (STA) is used to compute the emissivities, opacities, and average ionization states of carbon (C) and polystyrene (CH) plasmas in the warm-dense matter regime in which the coupling constant varies between 0.02 to 2.0. The accuracy of results of STA calculations is assessed by benchm...

A theoretical model based on the method of super transition arrays (STA) is used to compute the emissivities, opacities and average ionization states of carbon (C) and polystyrene (CH) plasmas in the warm-dense matter regime in which the coupling constant varies between 0.02 to 2.0. The accuracy of results of STA calculations is assessed by benchma...

A theoretical model based on the method of super transition arrays (STA) is used to compute the emissivities, opacities and average ionization states of carbon (C) and polystyrene (CH) plasmas in the warm-dense matter regime in which the coupling constant varies between 0.02 to 2.0. The accuracy of results of STA calculations is assessed by benchma...

We use a momentum-dependent optical model potential to analyze the annihilation cross sections of antineutron $\bar n$ on C, Al, Fe, Cu, Ag, Sn, and Pb nuclei for projectile momenta $p_{\rm lab}$ $\lesssim$ 500 MeV/$c$. We obtain good description of annihilation cross sections data of Barbina {\it et al.} [Nucl.~Phys.~A {\bf 612}, ~346~(1997)] and...

We use a momentum-dependent optical model potential to analyze the annihilation cross sections of antineutron $\bar n$ on C, Al, Fe, Cu, Ag, Sn, and Pb nuclei for projectile momenta $p_{\rm lab}$ $\lesssim$ 500 MeV/$c$. We obtain good description of annihilation cross sections data of Barbina {\it et al.} [Nucl.~Phys.~A {\bf 612}, ~346~(1997)] and...

DOI:https://doi.org/10.1103/PhysRevC.95.029901

We review the application of the time-dependent close-coupling method to the study of ion-impact ionization of atoms and molecules. Ionization cross sections are presented for bare ion, antiproton, and neutron collisions with light atoms and molecules.

We examine the momentum dependence of $\bar p$$p$ and $\bar n$$p$ annihilation cross sections by considering the transmission through a nuclear potential and the $\bar p p$ Coulomb interaction. Compared to the $\bar n p$ annihilation cross section, the $\bar p p$ annihilation cross section is significantly enhanced by the Coulomb interaction for pr...

Time-dependent close-coupling methods are used to calculate energy differential cross sections for the single and double ionization of He by impact with F9+ ions at 4.0 MeV amu−1. Single ionization energy differential cross sections using both a one active electron method and a two active electron method are compared with recent experimental result...

We perform R-matrix with pseudostates calculations to investigate single photon double ionization of Be@C60 and Mg@C60. We contrast the present results to our previous studies of He@C60. We find the presence of the confinement resonances in the double photoionization cross sections of endohedral Be and Mg. Keeping the same C60 spherical shell poten...

The static dipole polarizability of noble-gas atoms confined by impenetrable spheres and spherical shells is studied using the $B$-spline random phase approximation with exchange. The general trend in dipole polarizabilities across the noble-gas sequence shows a decrease in the dipole polarizability as the volume of the confining impenetrable spher...

An accurate knowledge of atomic collision processes is important for a better understanding of many astrophysical and laboratory plasmas. Collision databases which contain electron-impact excitation, ionization, and recombination cross sections and temperature dependent rate coefficients have been constructed using perturbative distorted-wave metho...

The time-dependent close-coupling method is used to calculate neutron-impact single and double ionization cross sections of the He atom. We also present the ratio of double to single ionization for He as a guide to experimental checks of theory at low energies and experimental confirmation of the rapid rise of the ratio at high energies unique to n...

A two active electron time-dependent close-coupling method is used to calculate antiproton-impact single ionization, ionization with excitation, and double ionization cross sections for H2 at low incident energies. Comparisons are made with LEAR/CERN and recent AD/CERN measurements for the ionization of H2 producing H+2 and with LEAR/CERN measureme...

The R-matrix with pseudostates (RMPS) and time-dependent close-coupling (TDCC) methods are used to calculate photoionization-excitation and double photoionization cross sections of He and He@C60.

An accurate two-dimensional ab initio potential energy surface of the He-C$_{3}$ collisional system is calculated using the supermolecular coupled-cluster method with up to perturbative quadruple excitations, CCSDT(Q). This interaction potential is then incorporated in full close-coupling calculations of rotational excitation/de-excitation cross se...

Previous analytical formulas in the Glauber model for high-energy nucleus-nucleus collisions developed by Wong are utilized and extended to study antiproton-nucleus annihilations for both high and low energies, after taking into account the effects of Coulomb and nuclear interactions, and the change of the antiproton momentum inside a nucleus. The...

We investigate the differential cross sections for antiproton-impact ionization of H atoms within the framework of time-dependent close-coupling theory. A Fourier transform method is employed in order to extract the fully differential cross sections for a specific value of projectile momentum transfer. The method allows us to incorporate the inform...

The R-matrix with pseudostates method is applied to the case of two-electron excitation and ionization processes in He@C60. A finite spherical-well potential, which simulates the effect of the fullerene enclosing cage, is incorporated into the Hamiltonian using a modified R-matrix method, as recently applied to similar single photoionization studie...

We present our progress in the investigations of atomic and molecular ionization due to antiproton-impact using the time-dependent close-coupling (TDCC) methods. We show some examples of our energy-dependent ionization cross sections for H, He, Li, H2+ and H2 and compare them with the available theoretical and experimental data.

Time-dependent close-coupling (TDCC), R-matrix-with-pseudostates (RMPS), and time-independent distorted-wave (TIDW) methods are used to calculate electron-impact ionization cross sections for the carbon atom. The TDCC and RMPS results for the 1s22s22p2 ground configuration are in reasonable agreement with the available experimental measurements, wh...

Background A meta-analysis of published data was conducted to investigate the overall risks of hypertension and QTc prolongation in patients with advanced non-small cell lung cancer (NSCLC) who were receiving vandetanib. Methods A computerized search through electronic databases, including PubMed and Embase (until Dec 2014), was performed to obtain...

Over the last decade an Auburn-Rollins-Strathclyde consortium has developed several suites of parallel R-matrix codes [1, 2, 3] that can meet the fundamental data needs required for the interpretation of astrophysical observation and/or plasma experiments. Traditionally our collisional work on light fusion-related atoms has been focused towards spe...

A large-scale 554 level R-matrix Intermediate Coupling Frame Transformation (ICFT) calculation is presented to provide a comprehensive electron-impact excitation data set for all transitions to higher n shells.

In anticipation of future experimental investigations of two-electron processes in endohedral atoms, the double photoionization and single photoionization with excitation of helium confined in the fullerenes C36, C60 and C82 have been studied using the time-dependent close-coupling method. It is found that both He@C60 and He@C82 display strong conf...

Antiproton-impact single ionization cross sections are calculated for both H+2 and H2. A one-active-electron time-dependent close-coupling method is used to calculate cross sections for H+2 at various molecular orientations for incident energies ranging from 1.0 to 200.0 keV. The results are compared with other theoretical results. Both one-active-...

Along with H2, HD has been found to play an important role in the cooling of the primordial gas for the formation of the first stars and galaxies. It has also been observed in a variety of cool molecular astrophysical environments. The rate of cooling by HD molecules requires knowledge of collisional rate coefficients with the primary impactors, H,...

A time-dependent close-coupling method, formulated within the framework of a rotational function expansion in two-dimensional cylindrical coordinates, is used to investigate excitation processes in proton-lithium collisions. As a first check, the calculated Li(1s22s)→Li(1s22p) excitation cross sections are compared and shown to be in reasonable agr...

Time-dependent close-coupling methods based on the expansion of one- and two-active-electron wavefunctions in spherical harmonics are used to calculate antiproton-impact single-ionization cross sections for H, He and Li. The single active electron cross sections are found to be in fair agreement with previous calculations and experiment for H and i...

Large-scale R-matrix calculations are carried out for the electron-impact excitation of Ne3+ and Ne6+. For Ne3+, a 581-LSJ-level R-matrix intermediate coupling frame transformation calculation is made for excitations up to the n=4 shell. For some transitions, large effective collision strength differences are found with current 23-jKJ-level Breit-P...

The five J levels within an np 2 or np 4 ground-state complex provide an excellent testing ground for the comparison of theoretical line ratios with astrophysically observed values, in addition to providing valuable electron temperature and density diagnostics. The low-temperature nature of the line ratios ensures that the theoretically derived val...

Excitation processes in proton collisions with Li are studied by direct solution of the time-dependent Schrödinger equation in cylindrical coordinates. Within a straight-line trajectory approximation, a time-dependent close-coupling method based on an expansion of a one-electron 3D wavefunction in rotational functions is used to calculate excitatio...

As most of the gas in the Universe is not in thermal equilibrium, accurate modeling and interpretation of observations requires understanding of a variety of collisional processes. Rate coefficients describing such processes can usually be measured and/or calculated, but the enormous enhancements in the spectral line resolution and sensitivity expe...

We examine the stability of matter-antimatter molecules by reducing the four-body problem into a simpler two-body problem with residual interactions. We find that matter-antimatter molecules with constituents (m1+, m2-, m2bar+, m1bar-) possess bound states if their constituent mass ratio m1/m2 is greater than about 4. This stability condition sugge...

DOI:https://doi.org/10.1103/PhysRevA.83.039908

The five J$\Pi$ levels within a $np^2$ or $np^4$ ground state complex provide an excellent testing ground for the comparison of theoretical line ratios with astrophysically observed values, in addition to providing valuable electron temperature and density diagnostics. The low temperature nature of the line ratios ensure that the theoretically deri...

The double photoionization of a helium atom and a singly charged lithium positive ion enclosed in charged Cq60 fullerenes is studied using the time-dependent close-coupling method. Continuum raising and lowering effects are seen in the shift of the double-ionization threshold of the confined atom or ion. Confinement resonances in the double-photoio...

Ionization processes in antiproton collisions with H2 are studied by direct solution of the time-dependent Schrödinger equation. A time-dependent close-coupling method based on an expansion of a one-electron 3D wavefunction in the field of H+2 is used to calculate single-ionization cross sections at incident energies ranging from 50 keV to 1.5 MeV....

We demonstrate the creation of vortices in the electronic probability density of an atom subject to short electric field pulses, how these vortices evolve and can be manipulated by varying the applied pulses, and that they persist to macroscopic distances in the spectrum of ejected electrons. This opens the possibility to use practical femtosecond...

Nonperturbative R-matrix-with-pseudostates (RMPS) and time-dependent close-coupling (TDCC) methods are used to determine electron-impact-ionization cross sections for the excited states of B, B{sup +}, and B{sup 2+}. RMPS calculated cross sections are presented for the 1s²2s²3l and 1s²2s²4l configurations of B, the 1s²2s3l and 1s²2s4l configuration...

We present calculations of the double ionization of H2 induced by an intense attosecond laser pulse at a photon energy of 40 eV using the time-dependent close-coupling method within the fixed nuclei approximation. We focus on two-photon absorption processes and examine how the response of the ejected electrons, in particular the single- and the dou...

A large set of calculations has been carried out providing a basis for diagnostics of fusion plasmas through emission resulting from radiative de-excitation following charge transfer between hydrogen and highly charged argon ions, so-called argon charge exchange recombination spectroscopy. These results have been obtained using the classical trajec...

Non-perturbative theoretical methods over the last decade have mainly focused on electron-impact ionization of the ground and first metastable states for light fusion related species [1]. However, collisional-radiative models predict that effective ionisation rates, which include the ionisation from excited levels of an atom, can be an order of mag...

Time-dependent close-coupling calculations within the fixed nuclei approximation are carried out for the double ionization of H2 induced by an intense attosecond laser pulse at a photon energy of 40 eV. We consider here the two-photon absorption processes and examine the response of the ejected electrons, particularly the single- and the double-ele...

The double photoionization of a He atom enclosed in a C60 molecule, He@C60 was investigated using the time-dependent close-coupling method with the C60 molecule represented by a spherical shell potential and the He atom treated nonperturbatively. Comparisons are made with the double photoionization of a bare He atom. The ratio of the total double p...

We examine the effect of theoretically varying the collision-system reduced mass in collisions of He with vibrationally excited molecular hydrogen and observe zero-energy resonances for select atomic “hydrogen” masses less than 1 u or a “helium” mass of 1.95 u. Complex scattering lengths, state-to-state vibrational quenching cross sections, and a l...

A brief overview is given of theoretical results for electron-impact ionization of atoms and ions. A description is given of the main theoretical methods, along with the databases where the data are archived. It is shown that for light species, ground and metastable ionization cross sections are in reasonable agreement with experiment when non-pert...

Ionization dynamics of atoms and molecules under attosecond laser pulses with various photon energies and peak intensities have been investigated using the Time-Dependent Close-Coupling (TDCC) method. We predict the chirp effects on the triply differential probabilities for the ionized electrons of He produced by 450 and 135 asec pulses. In additio...

Non-perturbative time-dependent close-coupling calculations are carried out for the double photoionization of helium including both dipole and quadrupole radiation effects. At a photon energy of 800 eV, accessible at current synchrotron light sources, the quadrupole interaction contributes around 6% to the total integral double photoionization cros...

Synopsis Using a novel computational approach, we have elucidated the origin of unexpected vortices in atomic collisions. It is shown how they could be observed in experiments and how they play a new and wide ranging role in angular momentum transfer. Vortices are usually associated with systems containing large numbers of particles. However, of pa...

An overview will be given of recent atomic and molecular collision methods developed to take advantage of modern massively parallel computers. The focus will be on direct solutions of the time-dependent Schrödinger equation for simple systems using large numerical lattices, as found in the time-dependent close-coupling method, and for configuration...

Based on the time-dependent close-coupling method, energy and angular differential probabilities for various ionization processes of He atoms subjected to intense attosecond soft-x-ray pulses with a photon energy of 91.6 eV and a peak intensity of 1015 W/cm2 are calculated to explore their dependence on the duration and the chirp of the pulse. It i...

Vortices are usually associated with systems containing large numbers of particles. Of particular topical interest though are those formed within atomic-scale wave functions and observed in macroscopic systems such as superfluids and quantum condensates. We uncover them here in one of the most fundamental quantum systems consisting of just one elec...

The time-dependent close-coupling (TDCC) method is used to investigate the energy and angular differential probabilities for various ionization processes of He atoms under chirped attosecond soft x-ray pulses with a photon energy of 91.6 eV and a peak intensity of 10^15 W/cm^2. It is shown that the ejected electrons probability density for two-phot...

Even though the static properties of quantum systems have been known since the early days of quantum mechanics, accurate simulation of the dynamical break‐up or ionization remains a theoretical challenge despite our complete knowledge of the relevant interactions. Simulations are challenging because of highly oscillatory exponential phase factors i...

The recent development of petascale computing systems has opened up new vistas for Atomic, Molecular and Optical (AMO) physics. To take full advantage of the new computational facilities, atomic physics codes must be parallelized with careful attention paid to identifying multiple levels of parallelization so as to enable efficient scaling to as ma...

Rate coefficients for rotational transitions in H(2) induced by H(2) impact are presented. Extensive quantum mechanical coupled-channel calculations based on a recently published (H(2))(2) potential energy surface were performed. The potential energy surface used here has been demonstrated to be more reliable than surfaces used in previous work. Ro...

The momentum transfer and viscosity cross sections for proton-hydrogen collisions are computed in the velocity range of ~200-20,000 km s−1 relevant to a wide range of astrophysical environments such as supernova remnant shocks, solar wind, winds within young stellar objects or accretion disks, and interstellar protons interacting with the heliosphe...

Total and state-selective cross sections for charge transfer in ~1–1000 keV/u He2+ + H collisions have been calculated using a variety of theoretical approaches, namely, the classical trajectory Monte Carlo, atomic-orbital close-coupling and lattice, time-dependent Schrödinger equation methods. Comparison of the results with available experimental...

In this study we examine the effects of varying the molecular mass on the complex scattering lengths in collisions of molecular hydrogen and He. The variation in the diatomic mass is effected by holding the mass of one atom constant while varying the mass of the other. Specifically, we examine the three cases where the fixed atom is one of the thre...

In recent years, with the increasing availability of powerful high performance computers, the direct numerical solution of time-dependent Schrodinger equation has become a desirable theoretical technique for investigating atomic and molecular collision processes. This quantitative and rigorous approach has been applied to solve various non-perturba...

Cross sections for dissociation of H2 due to collision with He are calculated for highly excited rovibrational states using the quantum mechanical coupled states approximation. An L^2 Sturmian basis set with multiple length scales is used to to provide a discrete representation of the H2 continuum which includes orbiting resonances and a non-resona...

We report the creation of vortex rings when an atom is exposed to very short electric field pulses. A full-dimensional time-dependent Schrodinger equation has been used to investigate the creation and the time-dependent dynamics of these vortex rings within the limit of weak and strong electric field intensities. The underlying conditions that cont...

Vortices are a nearly ubiquitous feature of nature. It is well known that they form in large scale processes such as weather, but they are also formed in the quantum realm. One place where they can be seen quite clearly is in the wave functions for ion- atom collisions at a set impact parameter. In this work we use a very low noise and highly accur...

Cross sections for dissociation of H2 due to collision with He are calculated for highly excited rovibrational states using the quantum-mechanical coupled-states approximation. An L2 Sturmian basis set with multiple length scales is used to provide a discrete representation of the H2 continuum which includes orbiting resonances and a nonresonant ba...

The lattice time-dependent Schrödinger equation (LTDSE) and atomic orbital close coupling (AOCC) methods are applied to calculate the charge transfer cross sections for H+ + He+ and He2+ + Li2+ collisions in the velocity range of 0.5–4.0 atomic units. The comparison of the results is made with those of other theoretical methods and with measurement...

We evaluate the interaction potential between a hydrogen and an antihydrogen using the second-order perturbation theory within the framework of the four-body system in a separable two-body basis. We find that the H-Hbar interaction potential possesses the peculiar features of a shallow local minimum located around interatomic separations of r ~ 6 a...

An ab initio, three-dimensional quantum mechanical calculation has been performed for the time-evolution of continuum electrons in the fields of moving charges. Here the essential singularity associated with the diverging phase factor in the continuum wave function is identified and removed analytically. As a result, the continuum components of the...

The success in creating Bose-Einstein condensates of molecules has spurred much interest in atom-molecule and molecule-molecule collisions at cold and ultracold temperatures. To understand the effect of rotational and vibrational relaxation in molecular collisions at ultracold temperatures we have performed quantum scattering calculations taking th...