Radial Coupling Research Articles

Ab initio many-electron study for the low-lying states of the alkali hydride cations in the adiabatic representation

An ab initio multireference single- and double-excitation configuration interaction (CI) study is carried out for the ground and excited electronic states of alkali-hydride cations (LiH(+), NaH(+), KH(+), RbH(+), and CsH(+)). For all alkali-metal atoms, the first inner-shell and valence electrons (nine active electrons, three for Li) are considered explicitly in the ab initio self-consistent-field and CI calculations. The adiabatic potential energy curves, radial and rotational couplings are calculated and presented. Short-range (∼3 a.u.) potential wells produced by the excitation of the inner-shell electrons are found. The depths of the inner potential wells are much greater than those of the outer wells for the CsH(+) system. The computed spectroscopic constants for the long-range potential well of the 2 (2)Σ(+) state are very close to the available theoretical and experimental data. The electronic states of alkali-hydrogen cations are also compared with each other, it is found that the positions of the potential wells shift to larger internuclear distances gradually, and the depths of these potential wells become greater with increasing alkali-metal atomic number. The relationships between structures of the radial coupling matrix elements and the avoiding crossings of the potential curves are analyzed. From NaH(+) to CsH(+), radial coupling matrix elements display more and more complex structures due to the gradual decrease of energy separations for avoided crossings. Finally, the behavior of some rotational couplings is also shown.

Development of a Finite Element Model for Blast Brain Injury and the Effects of CSF Cavitation

Blast-related traumatic brain injury is the most prevalent injury for combat personnel seen in the current conflicts in Iraq and Afghanistan, yet as a research community,we still do not fully understand the detailed etiology and pathology of this injury. Finite element (FE) modeling is well suited for studying the mechanical response of the head and brain to blast loading. This paper details the development of a FE head and brain model for blast simulation by examining both the dilatational and deviatoric response of the brain as potential injury mechanisms. The levels of blast exposure simulated ranged from 50 to 1000 kPa peak incident overpressure and 1–8 ms in positive-phase duration, and were comparable to real-world blast events. The frontal portion of the brain had the highest pressures corresponding to the location of initial impact, and peak pressure attenuated by 40–60% as the wave propagated from the frontal to the occipital lobe. Predicted brain pressures were primarily dependent on the peak overpressure of the impinging blast wave, and the highest predicted brain pressures were 30%less than the reflected pressure at the surface of blast impact. Predicted shear strain was highest at the interface between the brain and the CSF. Strain magnitude was largely dependent on the impulse of the blast, and primarily caused by the radial coupling between the brain and deforming skull.The largest predicted strains were generally less than 10%,and occurred after the shock wave passed through the head.For blasts with high impulses, CSF cavitation had a large role in increasing strain levels in the cerebral cortex and periventricular tissues by decoupling the brain from the skull. Relating the results of this study with recent experimental blast testing suggest that a rate-dependent strain-based tissue injury mechanism is the source primary blast TBI.

Single- and double-electron capture processes in low-energy collisions of N3+with He

Single-electron capture (SEC) and double-electron capture (DEC) processes in collisions of ground state N{sup 3+} (2s{sup 2} {sup 1}S) ions with He are investigated by using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio adiabatic potentials, radial and rotational coupling matrices utilized in QMOCC calculations, are obtained from the multireference single- and double-excitation configuration interaction approach. Total and state-selective SEC and DEC cross sections are presented in the low-energy range from 0.1 eV to 15 keV (i.e., 0.007 eV/u -1.07 keV/u) and rate coefficients in the temperature range from 10{sup 4} to 10{sup 7} K. Our results indicate that the SEC dominates the charge-transfer process in the considered energy region of this collision system and the SEC cross sections are nearly constant in the relatively high-collision energy region, while the DEC cross sections are about 2 orders of magnitude smaller. It is found that, for the SEC processes, in the dominant mechanisms, electrons are captured to exoergic channels N{sup 2+} (2s2p{sup 2} {sup 2}D,{sup 2}S), and for the DEC processes, they are captured to N{sup +} (2s{sup 2}2p{sup 2} {sup 1}D,{sup 1}S). Our calculations also reveal that rotational couplings become important at E > 10 eV/u for SEC andmore » E > 200 eV/u for DEC processes.« less

Generation of excitedKbands in heavy nuclei

It is known that coupling an intrinsic excitation of integer spin and positive parity ${I}^{+}$ to a rotor having a degenerate set of states ${L}^{\ensuremath{\pi}}={0}^{+},{2}^{+},{4}^{+},...,$ generates a series of $K$ bands. A given value of ${I}^{+}$ gives rise to several bands labeled by ${K}^{+}={0}^{+},{1}^{+},{2}^{+},...,{I}^{+}$, that is, a total of ($I+1$) such bands, in the spectrum of the combined system. We discuss how a binary cluster model of an excited core orbited by a spinless cluster can approximate these conditions. A crucial point is that the radial wave functions of relative motion are very similar for low $L$, and their radial coupling integrals even more so, such that the wave functions play the model role of a common intrinsic state for the lowest excited states of the system. If the core has a ${0}^{+}$ ground state and a low-lying ${2}^{+}$ excited state, then lifting the degeneracy leads to a ground state ${K}^{+}={0}^{+}$ band and low-lying excited ${K}^{+}={0}^{+}$, ${1}^{+}$, and ${2}^{+}$ bands. Although these are all seen in light nuclei, the ${K}^{+}={1}^{+}$ band is conspicuous by its apparent absence in heavy nuclei, and we urge experimental groups to reexamine their data for signs of it.

First and second derivative of the wave function of the1Σ+states of the KH molecule

First and second derivative of the nonadiabatic coupling between the several ${}^{1}\ensuremath{\Sigma}{}^{+}$ adiabatic states of the KH molecule considered from accurate diabatic and adiabatic data have been evaluated. Such derivatives of the electronic wave function are determined through a numerical differentiation of the rotational matrix connecting the diabatic and adiabatic representations. The first as well as the second derivative present many peaks related to ionic-neutral and neutral-neutral coupling between the ${}^{1}\ensuremath{\Sigma}{}^{+}$ states. Such radial coupling has been exploited to calculate the first adiabatic correction, which corresponds to the diagonal term of the second derivative divided by the reduced mass, for the ground and some excited states of the KH molecule. The second adiabatic correction has been determined using the virial theorem. The first adiabatic correction was added to the adiabatic potential energy curves to redetermine the corrected spectroscopic constants and vibrational energy levels. The vibrational shift, which is the difference between the corrected and the adiabatic levels, has been calculated for $X$, $A$, $C$, and $D$ ${}^{1}\ensuremath{\Sigma}{}^{+}$ states of the KH molecule. A shift of some 10 cm${}^{\ensuremath{-}1}$ is observed for some vibrational levels showing the breakdown of the Born-Oppenheimer approximation.

Sympathetic cooling of the Ba+ion by collisions with ultracold Rb atoms: Theoretical prospects

State-of-the-art {\em ab initio} techniques have been applied to compute the potential energy curves of the (BaRb)$^+$ molecular ion in the Born-Oppenheimer approximation. The long-range coefficients describing the electrostatic, induction, and dispersion interactions at large interatomic distances are also reported. The electric transition dipole moments governing the X$^1\Sigma \to ^1\Sigma, ^1\Pi$ have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Nonadiabatic radial and angular coupling matrix elements, as well as the spin-orbit coupling matrix elements have been evaluated using the multireference configuration interaction method restricted to single and double excitations with a large active space. With these couplings, the spin-orbit coupled (relativistic) potential energy curves for the 0$^+$ and 1 states relevant for the running experiments have been obtained. Finally, relativistic transition moments and nonadiabatic coupling matrix elements were obtained from the nonrelativistic results and spin-orbit eigenvectors. The electronic structure input has been employed in the single channel scattering calculations of the collisional cross sections between the Ba$^+$ ion and Rb atom. Both nonrelativistic and relativistic potentials were used in these calculations. Our results show that the inelastic cross section corresponding to the charge transfer from the Rb atom to the Ba$^+$ ion is much smaller than the elastic one over a wide range of energies up to 1 mK. This suggests that sympathetic cooling of the Ba$^+$ ion by collisions with ultracold Rb atoms should be possible.

Quantum dynamics of the charge transfer in C+ + S at low collision energies

Following a recent semiclassical investigation by Bacchus-Montabonel and Talbi (2008 Chem. Phys. Lett. 467 28), the C+(2s22p)2P + S(3s23p4)3P charge transfer process involved in the modellization of the interstellar medium chemistry and its reverse reaction are revisited by combining a wave packet approach and semiclassical dynamics in a quasimolecular approach for doublet and quartet states. New radial non-adiabatic coupling matrix elements have been calculated and the mixed treatment gives access to new precise values of the rate coefficients for the direct and reverse charge transfer processes. For this system, quantum and semiclassical results are in good agreement even at low collision kinetic energies. The dominance of the quartet states in the process is confirmed. In the quantum treatment, the collision matrix elements are extracted from wave packets by the flux method with an absorbing potential. The formation of resonances due to a centrifugal barrier is illustrated.

Ab initiocalculation ofH+He+charge-transfer cross sections for plasma physics

The charge-transfer in low-energy ($0.25$ to $150$ eV/amu) $\mathrm{H}(\mathit{nl})+{\mathrm{He}}^{+}(1s)$ collisions is investigated using a quasimolecular approach for the $n=2,3$ as well as the first two $n=4$ singlet states. The diabatic potential energy curves of the HeH${}^{+}$ molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge-transfer cross section on the principal and orbital quantum numbers $n$ and $l$ of the initial or final state. We estimate the effect of the nonadiabatic rotational couplings, which is found to be important even at energies below $1$ eV/amu. However, the effect is small on the total cross sections at energies below $10$ eV/amu. We observe that to calculate charge-transfer cross sections in an $n$ manifold, it is only necessary to include states with ${n}^{\ensuremath{'}}\ensuremath{\leqslant}n$, and we discuss the limitations of our approach as the number of states increases.

Ab initio ground and the first excited adiabatic and quasidiabatic potential energy surfaces of H + + CO system

Ab initio global adiabatic as well as quasidiabatic potential energy surfaces for the ground and the first excited electronic states of the H + + CO system have been computed as a function of the Jacobi coordinates ( R, r, γ) using Dunning’s cc-pVTZ basis set at the internally contracted multi-reference (single and double) configuration interaction level of accuracy. In addition, nonadiabatic coupling matrix elements arising from radial motion, mixing angle and coupling potential have been computed using the ab initio procedure [Simah et al. (1999) [66]] for the purpose of dynamics study. The geometrical properties corresponding to the minimum energy of the bound HCO + and HOC + isomers have been obtained and compared with those predicted by previous theoretical and experimental results. The HCO + has been found to be more stable than the HOC +. The minimum energy pathway in the ground electronic state for the isomerization process, HCO + ⇌ HOC + has also been obtained as a function of γ.

Isotope effects on the charge transfer into then=1, 2, and 3 shells ofHe2+in collisions with H, D, and T

Processes for charge transfer into ${\mathrm{He}}^{2+}$ colliding with the atomic isotopes hydrogen (H), deuterium (D), and tritium (T) are theoretically studied at collision energies as low as 30 eV/amu. Probabilities and cross sections for electron capture into different shells of the projectile are calculated using an ab initio approach which solves the time-dependent Schr\"odinger equation. The results are interpreted in terms of radial and rotational couplings between molecular orbitals. The probabilities exhibit strong Stueckelberg oscillations for charge transfer into shells with the principal quantum numbers $n=2$ and 3 due to radial coupling mechanisms in specific ranges of the impact parameter. The total cross sections for charge transfer, evaluated for a given shell, differ by orders of magnitude, as different isotopes are used in the collisions. The isotope effect increases significantly for decreasing $n=3$, 2, and 1. This finding is attributed to the influence of the rotational coupling mechanism, which is strongly affected by the distance of closest approach between the collision partners.

Enhanced radiation-loss-based radial-waveguide-coupled electrically pumped microresonator lasers with single-directional output

A novel enhanced radiation-loss (ERL)-based radial waveguide coupling mechanism for microresonator lasers is experimentally demonstrated for the first time, to the best of our knowledge, resulting in single-directional output from the lasers. A 20 microm diameter InGaAsP/InP electrically pumped microresonator laser in the form of a microcylinder resonator integrated with a transparent ERL radial output coupler is designed and fabricated. Measurement shows a low 1.5 mA lasing threshold and a relatively high output power of >0.4 mW.

Study on Chloride Diffusion in Concrete with Non-Homogenous Coefficient Using Meshless Boundary Element Method

A new robust numerical technique was proposed for analyzing chloride transient diffusion in concrete with non-homogenous coefficient. The method was based on a meshless boundary element method which results in an integral equation for explicitly evaluating field chloride quantities. Weighted residual method and Green’s function were adopted to derive domain and boundary integral equations. A radial integration method coupling with radial basis function approximation technology was used to convert domain integral into equivalent boundary integral. With central finite difference method, an explicit time iteration scheme was established for solving transient diffusion equation. Two numerical examples for 2D diffusion problem were given to demonstrate the robustness of the proposed method. Numerical results show that the non-homogenous diffusion coefficient causes the chloride distribution non-uniform, and the diffusion process is nonlinear with respect to time.

Ab initio calculations of charge transfer in He+ colliding with Ne

The charge-transfer cross sections for He+ colliding with Ne atoms are calculated for the incident energy ranging from 20 eV to 5 keV by a quantum-mechanical molecular-orbital close-coupling method, which utilizes ab initio adiabatic potentials, radial and rotational coupling matrix elements obtained with a multireference configuration interaction method. Total and state-selective cross sections and rate coefficients are presented. It is found that for the collision energy E < 0.8 keV, the main charge-transfer channels are capture to the 1s2s and 1s2p excited states of He, while for E > 0.8 keV, the capture to the 1s2 ground state becomes dominant. It is also found that rotational coupling becomes important for E > 0.6 keV.

Cross sections for low-energy inelastic H+Na collisions

Full quantum-scattering calculations are reported for low-energy near-threshold inelastic collision cross sections for $\mathrm{H}+\mathrm{Na}$. The calculations include transitions between all levels up to and including the ionic state (ion-pair production) for collision energies from the threshold up to 10 eV. These results are important for astrophysical modeling of spectra in stellar atmospheres. Results for the $3s\ensuremath{-}3p$ excitation are carefully examined using three different quantum chemistry input data sets, and large differences are found near the threshold. The differences are found to be predominantly due to differences in the radial coupling rather than potentials and are also found not to relate to differences in couplings in a simple manner. In fact, of the three input couplings, the two that are most similar give the cross sections with the largest differences. The $3s\ensuremath{-}3p$ cross sections show orbiting resonances which have been seen in earlier studies, while Feshbach resonances associated with closed channels were also found to be present in the low-energy cross sections for some transitions.

Ab initio calculation of the 66 low-lying electronic states of HeH+: adiabatic and diabatic representations

Using the quantum chemistry package MOLPRO and an adapted basis set, we have calculated the adiabatic potential energy curves of the first 20 1Σ+, 19 3Σ+, 12 1Π, 9 3Π, 4 1Δ and 2 3Δ electronic states of the HeH+ molecular ion in CASSCF and CI approaches. The results are compared with previous works. The radial and rotational non-adiabatic coupling matrix elements as well as the dipole moments are also calculated. The asymptotic behaviour of the potential energy curves and of the various couplings between the states is also studied. Using the radial couplings, the diabatic representation is defined and we present an example of our diabatization procedure on the 1Σ+ states.

Ab initiomolecular treatment for charge transfer byP3+ions on hydrogen and helium

A theoretical treatment of charge-transfer processes induced by collision of phosphorus ${\mathrm{P}}^{3+}(3{s}^{2}){}^{1}S$ ions on atomic hydrogen and helium has been carried out using ab initio potential-energy curves and couplings at the multireference configuration interaction level of theory. The cross sections calculated by means of semiclassical collision methods show the existence of a significant charge transfer in the $0.1\ensuremath{-}700$-keV laboratory energy range. Radial and rotational coupling interactions were analyzed for both collision systems.

Accurate ab initio potential energy curves for the classic Li–F ionic-covalent interaction by extrapolation to the complete basis set limit and modeling of the radial nonadiabatic coupling

Multireference configuration interaction calculations using large correlation consistent basis sets and full configuration interaction calculations with the smallest of such basis are utilized to describe the ionic-neutral curve crossing for the title system. The results of the former calculations have then been extrapolated to the complete basis set limit using the uniform singlet- and triplet-pair extrapolation scheme. A recent suggestion for locating the nonadiabatic matrix terms at the point where the dynamical correlation split vanishes has also been tested. Additionally, a consistent formalism is suggested to model the radial dependence of the nonadiabatic matrix terms that warrants an overlap dependence away from the crossing. When applied to LiF, the overall approach yields results in excellent agreement with the commonly accepted values for the geometric and energetic attributes at both the equilibrium and diabatic crossing regions.

On the origin of the asymmetric shape of the HCl photodissociation cross section

A first principles treatment of the photodissociation of HCl and DCl from 50 000 cm −1 to 75 000 cm −1 is presented. The treatment is the first to correctly reproduce the asymmetric absorption profile observed for HCl. The theoretical model for the HCl and DCl photodissociation presented in this study considers a dissociation process that occurs on a repulsive electronic state (A 1Π) coupled to a bound electronic state (C 1Π). The asymmetry in the HCl cross section arises because of the radial coupling introduced by the rotation-free nuclear kinetic energy operator.

Development of a Disposable Maglev Centrifugal Blood Pump Intended for One‐Month Support in Bridge‐to‐Bridge Applications: In Vitro and Initial In Vivo Evaluation

MedTech Dispo, a disposable maglev centrifugal blood pump with two degrees of freedom magnetic suspension and radial magnetic coupling rotation, has been developed for 1-month extracorporeal circulatory support. As the first stage of a two-stage in vivo evaluation, 2-week evaluation of a prototype MedTech Dispo was conducted. In in vitro study, the pump could produce 5 L/min against 800 mm Hg and the normalized index of hemolysis was 0.0054 +/- 0.0008 g/100 L. In in vivo study, the pump, with its blood-contacting surface coated with biocompatible 2-methacryloyloxyethyl phosphorylcholine polymer, was implanted in seven calves in left heart bypass. Pump performance was stable with a mean flow of 4.49 +/- 0.38 L/min at a mean speed of 2072.1 +/- 64.5 rpm. The maglev control revealed its stability in rotor position during normal activity by the calves. During 2 weeks of operation in two calves which survived the intended study period, no thrombus formation was seen inside the pump and levels of plasma free hemoglobin were maintained below 4 mg/dL. Although further experiments are required, the pump demonstrated the potential for sufficient and reliable performance and biocompatibility in meeting the requirements for cardiopulmonary bypass and 1-week circulatory support.

A comprehensive gyrokinetic description of global electrostatic microinstabilities in a tokamak

It is believed that low frequency microinstabilities such as ion temperature gradient (ITG) driven modes and trapped electron modes (TEMs) are largely responsible for the experimentally observed anomalous transport via the ion and electron channels in a tokamak. In the present work, a comprehensive global linear gyrokinetic model incorporating fully kinetic (trapped and passing) electrons and ions, actual ion to electron mass ratio, radial coupling, and profile variation is used to investigate the ITG driven modes and pure TEMs. These modes are found to exhibit multiscale structures in the presence of nonadiabatic passing electrons. The multiscale structure is related to the large nonadiabaticity of electrons in the vicinity of mode rational magnetic surfaces and leads to reduced mixing length estimates of transport compared to those obtained from adiabatic electron models.