Investigation of the electronic structure of Be2+He and Be+He,and static dipole polarisabilities of the helium atom

The potential energy and spectroscopic constants of the ground and many excited states of the Be⁺He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be²⁺ core and the electron-He interactions by effective potentials. Furthermore, the core–core interactions are incorporated. This permits the reduction of the number of active electrons of the Be⁺He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin–orbit interaction. The core–core interaction for Be²⁺He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be⁺He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole moment has been determined for a large and dense grid of internuclear distances including the spin orbit effect. In addition, a vibrational spacing analysis for the Be²⁺He and Be⁺He ground states is performed to extract the He atomic polarisability.     

A new determination of the partial widths of the 16.11 MeV state in 12C

The partial widths of the second T = 1 state of ¹²C, at 16.11 MeV excitation energy, have been determined by measuring the ¹¹B(p, γ) and ¹¹B(p, α) cross sections at the E_p = 163 keV resonance corresponding to this state. These measurements result in the new values of Γ_p = 21.7 ± 1.8 eV and Γ_γ = 21.6 ± 3.3 eV, for the partial widths of this state; approximately 3 times smaller and larger, respectively, than the present values in the literature. The new result for the proton width eliminates a serious discrepancy found in an earlier comparison of the partial widths of the T = 1 analogue states of the A = 12 system. Measurements were also made of the ¹¹B(d, n)¹²C¹ reaction to compare the proton widths of the 15.11 and 16.11 MeV T = 1 states; these measurements confirm the new, smaller proton width for the 16.11 MeV state. An attempt was also made to determine the γ-width of the 16.11 MeV state by measuring the γ-branching ratio in the ¹⁰B(³He, p)¹²C¹(γ)¹²C reaction.     

The characteristics for H<Subscript> 2</Subscript><Superscript> +</Superscript>-like impurities confined by spherical quantum dots

The energy spectra of H₂ ⁺-like impurities confined in finite spherical quantum dots have been calculated as a function of the distance between nuclear with different sizes on the basis of effective-mass approximation by linear variational method. B-splines have been used as basis functions, which can easily construct the trial wavefunctions with appropriate boundary and cusp conditions. The quantitative analyses of the partial wave weights for ground state and some low lying states have been done.     

States of5He and8Be from the reaction7Li+d

Nuclear reactions of deuterons with⁷Li have been used in order to determine properties of the intermediate nuclei⁸Be and⁵He. Of particular interest are locations and widths of the ground state and first excited state of⁵He, and of the second excited state of⁸Be. In a completeα-α-coincidence spectrum, however, overlapping of the coincident rates restricts very much the evaluation of such spectra. Particularly important is the velocity of the over-all center of mass which may cause unfavourable conditions for reliable determinations of the wanted data.     

Experimental investigation of the muon transfer reaction from deuterium to helium isotopes

Muon transfer from the ground state of muonic deuterium to a helium atom proceeds mainly via the formation of a muonic molecule in an excited state. A large number of decay X rays ( 6.8 keV) from these (dµHe)^* molecules were observed for the⁴He as well as for the³He case. The time distributions of these X rays allow the determination of the ground state transfer rate. The simultaneous employment of Ge/Si-detectors and CCDs for the same target conditions allows the determination of the branching ratio of radiative to nonradiative decay for the first time.     

Spontaneous emission of light from atoms: the model

We investigate (non‐relativistic) atomic systems interacting with quantum electromagnetic field (QEF). The resulting model describes spontaneous emission of light from a two‐level atom surrounded by various initial states of the QEF. We assume that the quantum field interacts with the atom via the standard, minimal‐coupling Hamiltonian, with the A² term neglected. We also assume that there will appear at most single excitations (photons). By conducting the analysis on a general level we allow for an arbitrary initial state of the QEF (which can be for instance: the vacuum, the ground state in a cavity, or the squeezed state). We derive a Volterra‐type equation which governs the time evolution of the amplitude of the excited state. The two‐point function of the initial state of the QEF, integrated with a combination of atomic wavefunctions, forms the kernel of this equation.     

Ground and Singlet Excited State Pyridinic Protonation of N9-Methylbetacarboline in Water-N,N-Dimethylformamide Mixtures

The ground and the singlet excited state pyridinic protonation of 9-methyl-9H-pyrido[3,4-b]indole, MBC, in water-N,N-dimethylformamide mixtures has been studied by absorption, steady state and time resolved fluorescence measurements. These proton transfer reactions elapse by a stepwise mechanism modulated by different hydrogen bonded adducts and exciplexes formed by water molecules and the pyridinic nitrogen atom of the MBC. Based in the present and previous studies, a general mechanistic Scheme for the ground and the singlet excited state MBC pyridinic protonation has been proposed. Accordingly, in the ground state, upon increasing the water proportion of the water-N,N-dimethylformamide mixtures, a hydrogen bonded complex, HBC, its hydrogen bonded proton transfer complex, PTC, a pre-cationic complex, PC, and the cation, C, are progressively formed. In the excited state, MBC, HBC and PC behave as independent fluorophores. Excited state cations, C*, are mainly formed by direct excitation of the ground state cations and, in minor proportion, by the excited state reaction of the PTC^* through the CL^* exciplex.     

Recent progress in simulation of the ground state of many Boson systems

We present two recent advances in the simulation of ⁴He in the condensed phase at zero temperature. Within the variational theory of strongly interacting bosons we have studied a cluster of ⁴He atoms with one alkali ion K⁺. For the wave function we have used a new shadow wave function (SWF) in which the coupling between one ⁴He atom and its shadow variable depends on its distance from the ion. This substantially improves the energy. The first shell around the ion contains 14 atoms which are spatially ordered. However the atoms of the first shell are not completely localized and frequent exchanges with atoms which are further from the ion take place. This also suggests that at least for the ion K⁺ the atoms of the first shell participate in the superfluidity. We have also introduced a new extension of the path integral ground state (PIGS) method which is able to compute exact ground state expectation values without extrapolations and with a SWF as the trial variational wave function to project on the ground state. This is an important extension which opens up the possibility of studying disorder phenomena in the solid phase by an exact method at zero temperature. We have applied this technique to compute the energy of formation of a vacancy at different densities in the solid phase of ⁴He. This computation confirms the variational result that a vacancy is a delocalized defect in the low density helium solid.     

Theoretical study of the Ru + CH3F reaction

CASSCF-MRMP2 calculations have been performed to analyse the reaction of fluoromethane with a bare ruthenium atom. Potential energy curves emerging from the ground state and the first excited state of the reactants, Ru(⁵F, ³F;d⁷s¹) + CH₃F, were calculated for representative electronic states associated with different approaching modes of the fragments. Whereas no favourable channels correlating with the ground state asymptote were detected for the insertion of the ruthenium atom into the C–H bond of the methyl fluoride molecule, the oxidative addition of the C–F bond of this molecule to the metal atom along the reaction path evolving from the ground state of the fragments leads to the stable inserted product CH₃–Ru–F. Although forming less stable products, insertion of ruthenium into the C–H and C–F bonds of the fluorocarbon molecule can occur through electronic states which emerge from the excited triplet state asymptote.     

Tunneling between double wells of atom in crossed electromagnetic fields

The tunneling between double wells of atom in crossed electromagnetic fields is investigated by a one-dimensional Hamiltonian model. The crossed fields induced outer well is apart from the nuclear origin and it is very difficult to access by means of spectroscopy but it will be possible if there exists the tunneling of the electron between the outer well and the Coulomb potential predominated well at the nuclear origin. A one-dimensional quantum calculation with B-spline basis has been performed for hydrogen atom in crossed fields accessible in our laboratory, at B=0.8~T and F=-220~V.cm^-1. The calculation shows that the wavefunctions of some excited states close to the Stark saddle point in the outer well extend over to the Coulomb potential well, making it possible to penetrate the quantum information of the outer well. However, the tunneling rate is very small and the spectral measurement of the transitions from the ground state should be of a high resolution and high sensitivity.     

TDHF study of the He+ collision on atomic He targets at the8Be ground state energy

Experimentally the⁸Be ground state resonance has been studied in He⁺ collisions on atomic He atoms. The nuclear resonance manifests itself by satellite resonance lines corresponding to different electron configurations of the Be ion. Experimentally a large probability for the emission of one electron has been deduced. We study the atomic He⁺+He collision within a model in which the evolution of the electron wavefunction is treated dynamically in the TDHF scheme, and the motion of the nuclei is treated classically. In agreement with experiment we find a large probability for one electron to be emitted into the continuum during the lifetime of the⁸Be ground state resonance.     

Total Born cross sections for positronium and helium atom scattering

A thorough and systematic study has been performed for positronium (Ps) and helium (He) atom scattering using the first Born approximation. As a first step, the direct scattering has been studied. Here excitations of both the Ps atom and He atom, the ionization of the Ps atom with all the excitations of the He atom, the ionization of the He atom with all the excitations of the Ps atom and the ionizations of both the Ps and He atoms are taken into consideration. For the different states of the He atom, the wavefunctions suggested by Winter and Lin [Phys. Rev. A 12 (1975) 434] are used. For the ionization channels the continuum Coulomb wavefunctions have been taken for the ionized electrons.     

Shell model calculations on natural parity states in 10≦ A≦14 nuclei

Shell model calculations of natural parity states in the 10≦A≦14 mass region have been performed by assuming an inert⁴He core with the residual interaction in the 1p shell only. The modified surface delta interaction (MSDI) has been used as an effective two-body interaction. The MSDI parameters as well as the single-particle binding energies have been deduced from a least-squares fit to experimentally known levels in, firstly, the seperate¹⁰B,¹¹B-C,¹²C,¹³C-N and¹⁴N nuclei, and secondly, the whole mass region 10≦A≦14. Multipole moments for ground states and M1 and E2 radiative widths for excited states have been calculated with the resultant wave functions.     

Finite-range DWBA analyses of (dt) and (d3He) reactions on 64Zn at Ed = 13 MeV

Exact finite-range DWBA analyses of ($\text{d}\text{, t}\text{)}$ and $\text{(}\text{d}\text{d}$, ³He) reactions have been performed for an ⁶⁴Zr target at an incident deuteron energy of 13.0 MeV, leading to the ground states of the residual nuclei. The microscopic overlap functions for (d, t) and (d, ³He) systems obtained by using the Phillips triton wavefunctions have been used as projectile form factors into the calculation. The results are compared with zero-range DWBA calculations taking the finite-range effects into account by means of a local energy approximation. The results obtained by finite-range and zero-range calculations for differential cross sections as well as vector and tensor analysing powers are compared with the experimental data. The range of validity of the local energy approximation is discussed.     

He同位素与H2分子碰撞第二振动激发分波截面的理论研究

用公认精确度较高的密耦近似方法计算了不同能量下惰性气体原子³He（⁴He,⁵He）与H₂分子替代碰撞体系的00-20,00-22,00-24,00-26第二振动激发分波截面.通过分析³He（⁴He,⁵He）-H₂碰撞体系第二振动激发分波截面的差异,总结出³He（⁴He,^{5关键词： 振动激发 分波截面 密耦方法 同位素}     

(n,t) and (n, α) reactions on 9Be

A metallic ⁹Be target was bombarded with 13.99 MeV neutrons; α-particles, tritons and ⁶He recoil nuclei were detected and identified with a telescope consisting of two proportional counters and a solid state detector. Absolute differential cross sections were measured for the (n, t) reactions leading to the ground state and first excited state of ⁷Li and for the (n, α) reactions leading to the ground state and first excited state of ⁶He. No evidence for higher excited states in ⁶He has been found. An attempt has been made to interpret the observed (n, α) angular distributions in terms of the direct reaction model.     

The importance of nucleon substructure in nuclear ground states

Using a potential model, constrained by the hadron spectrum, for the confinement of relativistic quarks we explore the consequences of the substructure of nucleons for the binding energy and ground state wavefunction of ⁴He. In its simplest form, this model gives a binding energy of 19 MeV. Quark wavefunctions differ from those associated with free nucleons by less than 10%, the rms quark radius is 1.34 fm and the resulting structure differs considerably from that of an expansion beginning from the (0s)⁴ shell model. Considerable contributions to the binding energy, attractive from quark delocalization and repulsive from the quark hyperfine interaction, appear unavoidable. We conclude that these effects cannot be excluded from a detailed understanding of the properties of nuclear ground states.     

The spin density and the optical spectrum of CoCl2- 4

The CoCl^2- ₄ ion has been studied using ab initio methods at various levels of approximation (RHF, UHF, CI and MC SCF). The calculations have been performed both with and without the Madelung field from crystalline surroundings. One of the main purposes has been to investigate the spin density, and determine its dependence on both correlation and external fields. The spin density is found to be fairly dependent on correlation but rather independent of the surrounding crystal. The lower excited quartet states have been calculated using CI expansions based upon ground state RHF and MC SCF wavefunctions. The experimental spectrum is very well reproduced on the MC SCF/CI level, both with and without the Madelung field.     

Helium-cluster decay widths of molecular states in beryllium and carbon isotopes

⁴He (i.e., α particle) and ⁶He emissions from possible molecular states in beryllium and carbon isotopes have been investigated using a mean-field-type cluster potential. Calculations can reasonably describe the α-decay widths of studied states in beryllium and carbon isotopes, and also ²⁰Ne, compared with experiments. For the nucleus ¹⁰Be, we discussed α-decay widths with different shapes or different decay modes, in order to understand the very different decay widths of two excited states. The widths of ⁶He decays from ¹²Be and α decays from ^13,14C are predicted, which could be useful for future experiments.     

A study of 3He-4He tunneling motion in solid 3He-4He mixtures by means of T1ϱ measurements

³He spin relaxation time in the rotating frame (T_1?) has been measured for 2% ³He in ⁴He solid samples of different molar volume at exchange plateau region (0.5 K). From the data, the characteristic frequency by which a ³He atom exchanges its position with a neighboring ⁴He atom is determined.