Showing papers on "Ground state published in 1972"

A local exchange-correlation potential for the spin polarized case: I

Abstract: The local density theory is developed by Hohenberg, Kohn and Sham is extended to the spin polarized case. A spin dependent one- electron potential pertinent to ground state properties is obtained from calculations of the total energy per electron made with a 'bubble' (or random phase) type of dielectric function. The potential is found to be well represented by an analytic expression corresponding to a shifted and rescaled spin dependent Slater potential. To test this potential the momentum dependent spin susceptibility of an electron gas is calculated. The results compare favourably with available information from other calculations and from experiment. The potential obtained in this paper should be useful for split band calculations of magnetic materials.

Correlation Problems in Atomic and Molecular Systems. IV. Extended Coupled-Pair Many-Electron Theory and Its Application to the B H 3 Molecule

Abstract: The equations of the coupled-pair many-electron theory (CPMET) are extended to incorporate the effect of both unlinked and linked triexcited clusters. The minimal basis correlation energy of the B${\mathrm{H}}_{3}$ molecule in the ground state is calculated using the ordinary as well as extended CPMET in various degrees of approximation, and the relative importance of linked and unlinked triexcited clusters is studied. The results afford an unambiguous conclusion for closed-shell systems that, in contrast to the situation with tetraexcited states, unlinked triexcited clusters are negligible relative to the linked ones. It is shown that the extended CPMET reproduces the full configuration-interaction results to a very high degree of accuracy.

Triatomic Photofragment Spectra: I. Energy Partitioning in NO2 Photodissociation,

Abstract: The photofragment spectrum of NO2 has been measured in the near ultraviolet at 28 810 cm−1. A molecular beam of NO2 is crossed with brief pulses of polarized laser light and measurements are made on the distributions of speed and direction of the recoiling O and NO fragments produced by photodissociation. The average translational energy of the fragments is about 60% of the available energy. There are at least two prominent peaks in the translational energy distribution. We conclude that the two peaks most likely correspond to nearly equal probability of recoil with the NO fragment in the v=0 and v=1 vibrational states. Such vibrationally excited NO fragments produced by photodissociation in polluted atmospheres could perhaps react with different rates than ground state fragments. The positions and widths of the peaks indicate that there is a significant rotational distribution. Statistical and direct models for photodissociation energy partitioning are briefly explored, and their predictions compared wit...

Electronic structure of superheavy atoms

Abstract: We describe the status of the problem of the electron structure of superheavy atoms with nuclear charge Z > Zc ; here Zc≈170 is the critical value of the nuclear charge, at which the energy of the ground state of the 1S1/2 electron reaches the limit of the lower continuum of the solutions of the Dirac equation (∊ = - mec2) . We discuss the dependence of Zc on the nuclear radius R and on the character of the distribution of the electric charge inside the nucleus, and also the form of the wave functions at Z close to Zc . Owing to the Coulomb barrier , the state of the electron remains localized at Z > Zc , in spite of the fact that its energy approaches the continuum. An analysis of the polarization of the vacuum in a strong Coulomb field shows that a bare nucleus with supercritical charge Z > Zc produces spontaneously two positrons and, in addition a charge density with a total of two units of negative charge in the vacuum. The distribution of this density is localized in a region of dimension r ~ ħ/mec at the nucleus. The possibility of experimentally observing the effect of quasistatic production of positrons in the collision of two bare uranium nuclei (i.e., without electrons) is discussed. A brief review is presented of work on the motion of levels with increasing depth of the potential well in other relativistic equations (Kelin-Gordon, Proca, etc.).

Direct Measurement of the Vibrational Lifetimes of Molecules in Liquids

Abstract: A normal molecular vibration is strongly excited by a picosecond light pulse. The rise and decay of the excess population of the first excited vibrational state (electronic ground state) is observed with a delayed probe pulse. These measurements give, for the first time, values of the lifetimes of molecular vibrations in liquids.

Electron Spectroscopy of Open‐Shell Systems: Spectra of Ni(C5H5)2, Fe(C5H5)2, Mn(C5H5)2, and Cr(C5H5)2

Abstract: The high resolution HeI electron spectra of Ni(C5H5)2, Fe(C5H5)2, Mn(C5H5)2, and Cr(C5H5)2 have been recorded and analyzed in terms of a molecular orbital description of the electronic structure. The ground state electronic configurations have been assigned by considering the feasible ground state configurations, determining the number and type of ionic states obtained from ionization of these configurations, and then comparing the predicted transitions with those observed experimentally. The ground state configuration and adiabatic first ionization potential of these molecules are: Cr(C5H5)2, ··· (e2g)3(a1g)1, 3E2g, I.P.=5.50 eV; Mn(C5H5)2, ··· (e2g)4 (a1g)1, 2A1g, I.P.=6.55 eV; Fe(C5H5)2, ··· (a1g)2 (e2g)4, 1A1g, I.P.=6.72; Ni(C5H5)2, ··· (a1g)2 (e2g)4 (e1g)2, 3A2g, I.P.=6.2 eV. Vibrational structure has been observed in the spectrum of ferrocene and is assigned to progressions in ν4, the symmetric ring‐metal stretching mode.

Ion-molecule reactions of the rare gases with hydrogen. Part 1.—Diatomics-in-molecules potential energy surface for ArH+2

Abstract: Potential energy surfaces for the reactions Ar++ H2→ArH++ H and Ar + H+2→ArH++ H (ArH+ in the ground state) are calculated by the method of diatomics-in-molecules (DIM), the theory of which is conveniently summarized in matrix notation. Diatomic ArH+ and ArH curves needed for the method are obtained from ab initio SCFMO calculations. The shape of the ArH+2 surface appears to be consistent with the known experimental information for this system. Approximate calculations of collinear surfaces for the ground states of KrH+2 and NeH+2 are obtained by appropriate scaling of the ArH+ diatomic curves. Comparison of these surfaces with the ArH+2 surface results in a consistent rationalization of the available experimental data on the rare gas-hydrogen ion-molecule reactions. Gross differences in the behaviour of these reactions are related primarily to changes in the ionization potentials of the rare gas atoms. This has a profound effect on the shapes of the potential energy surfaces, particularly in the entrance valley, where there is a crossing between surfaces associated with the differently charged reactant species.

Condensation of excitons in germanium and silicon

Abstract: The ground state energy of an electron-hole plasma in a Ge type semiconductor is calculated with the help of the 'improved RPA' approximation of Nozieres and Pines (1958). The detailed band structure is taken into account, except for the warping of the valence band. That is, the effects of the anisotropy, of the valence band coupling and of the multivalley structure are discussed, and are found to stabilize the plasma. The numerical results for Ge and Si are in very good agreement with experiments, which provides a check for the validity of the 'improved RPA' approximation.

Photoabsorption by ground-state alkali-metal atoms.

Abstract: Principal-series oscillator strengths and ground-state photoionization cross sections are computed for sodium, potassium, rubidium, and cesium The degree of polarization of the photoelectrons is also predicted for each atom The core-polarization correction to the dipole transition moment is included in all of the calculations, and the spin-orbit perturbation of valence-p-electron orbitals is included in the calculations of the Rb and Cs oscillator strengths and of all the photoionization cross sections The results are compared with recent measurements

Photochemical characteristics of cyanine dyes. Part 1.—3,3′-diethyloxadicarbocyanine iodide and 3,3′-diethylthiadicarbocyanine iodide

Abstract: The dyes 3,3′-diethyloxadicarbocyanine iodide (DODI) and 3,3′-diethylthiadicarbocyanine iodide (DTDI) were investigated using laser and conventional flash photolysis techniques. In both cases direct excitation results in the formation of a photo-isomer having an absorption similar to and slightly to the red of the normal ground state absorption. The quantum efficiency for photo-isomer formation in both cases is less than 0.1. The quantum efficiency for intersystem crossing to the triplet state was observed to be < 0.01 in both cases and the triplet state extinction coefficients and spectra were therefore obtained by energy transfer techniques. The quantum efficiencies for fluorescence and radiative lifetimes obtained indicated that the fluorescence lifetimes were 1.24 and 1.20 ns for DODI and DTDI respectively.

Near Hartree‐Fock Calculations on the Ground State of the Water Molecule: Energies, Ionization Potentials, Geometry, Force Constants, and One‐Electron Properties

Abstract: Near Hartree‐Fock wavefunctions have been calculated for the ground state of the water molecule using both Slater and contracted Gaussian basis sets. Total energies of −76.063 hartree were obtained with a (5s4p1d/3s1p) Slater basis and a [6s5p2d/3s1p] contracted Gaussian basis derived from an (11s7p2d/5s1p) primitive set; these energies are estimated to be within 0.003±0.002 hartree of the Hartree‐Fock limit. The Hartree‐Fock wavefunctions account for ∼70% of the dissociation energy of water. The Hartree‐Fock vertical ionization potentials (in electron volts), 11.1(2B1), 13.3(2A1), and 17.6(2B2), are too low by 1–1.5 eV as expected. With the Gaussian basis set a potential surface was computed and the equilibrium geometry and harmonic force constants were calculated. The calculated bond length, 0.941 A, and bond angle 106.6°, are in good agreement with the experimental values, 0.957 A and 104.52°. In spite of the rather good agreement for the geometry, the force constants are in error by 15%–20%. This is a...

Electronic Energy Transfer Phenomena in Rare Gases

Abstract: In this paper we present the results of an experimental study of electronic energy transfer in xenon‐argon, krypton‐argon, and xenon‐krypton gaseous mixtures excited by a pulsed electric discharge. Spectroscopic evidence for electronic energy transfer is based on the decrease in the intensity of the vacuum ultraviolet emission of the excited diatomic homonuclear rare gas molecules in the presence of small amounts (10–1000 ppm) of a foreign rare gas atom, while the visible emission spectrum of the host gas is parctically unmodified under these conditions. The relative contributions of two energy transfer mechanisms involving atom‐atom and molecule‐atom energy transfer were established by a kinetic analysis of the dependence of the energy transfer efficiency on the host pressure. We have determined the cross sections for energy transfer from the lowest metastable Ar and Kr excited states, and from the lowest excited state of Ar2* and Kr2* to ground state Xe, and from metastable excited Ar and from Ar2* to ground state Kr. The molecule‐atom energy transfer process is characterized by large ∼ 10−14 cm2 cross sections. A simplified theoretical treatment of excited molecule‐ground state atom collisions provides a proper rationalization of these large cross sections in terms of long range dipole‐dipole coupling.

Calculation of Rotational and Vibrational Transitions for the Collision of an Atom with a Rotating Vibrating Diatomic Oscillator

Abstract: A practical method is presented for computing the T‐matrix elements for a rotating, vibrating oscillator. A simple model is used which approximates the features of the He–H2 system. It is found that the rigidrotor approximation is in error even at energies well below the threshold for vibrational excitation. For computation of rotational transitions from the ground to the first accessible excited rotational state, many of the excited rotational transitions may be neglected but some of the excited vibrational transitions must be included. At high energies, it is shown that for any particular transition many of the states not strongly coupled to the states involved in the transition may be neglected. It is found that the computation of T‐matrix elements for vibrational transitions in the presence of rotational transitions is not prohibitively time consuming. In computing the total cross section, it is shown that a calculation including only the ground state gives remarkably good results.

Ground and first excited states of excitons in a magnetic field

Abstract: An exact calculation of the ground state and of the first excited state withm = 0 and even parity of a hydrogenic system in a magnetic field is described, and results are given for the energy and the main features of the wave functions. Tor the excited state the shape of the nodal surface is given, and it is shown that in this case no contradiction exists between the noncrossing rule and the nodal-surface criterion for the connection of the levels in the low- and high-field regions.

Absorption Spectra of Ne2 and HeNe Molecules in the Vacuum‐uv Region

Abstract: The absorption spectra of the Ne2 and HeNe molecules have been investigated in the 585–760 A region with a 6.65 m vacuum spectrograph using the helium continuum as a background source. Twelve discrete band systems are identified in the Ne2 spectrum. The ground state is stable, with a potential depth De=30.2 cm−1, supporting two stable vibrational levels, v=0 and 1, and with B0=0.17 cm−1, giving r0=3.1 A. A number of existing intermolecular potential calculations agree with these results. State designations, dissociation products, stabilities, and observed transitions are discussed, and analogies are drawn with a previous study of the Ar2 molecule. It is suggested that the observed band systems represent members of Rydberg series converging to some of the Ne2+ states derived from atom combinations Ne (2p6 1S0)+ Ne+ (2p5 2P3/2,1/20). In addition, six band groups are attributed to the HeNe molecule. Here the ground state potential supports only one vibrational level, v=0.

Microwave Spectrum of cis‐Glyoxal

Abstract: The rotational spectrum of glyoxal has been investigated in the region from 18.0 to 40.0 GHz. Only B-type transitions were observed. Both Q-branch and R-branch assignments have been made for the ground state, and the Q-branch assignment has been made for the first excited state of the internal rotational mode. From relative intensity measurements of vibrational excited states, the torsional vibration is found to have a frequency of 114 plus or minus 8 per cm. From a consideration of the rotational constants, it is concluded that the isomer giving rise to the microwave spectrum is the planar cis form and not the gauche isomer. The dipole moment was determined to be 4.8 plus or minus 0.2 D.

Vacuum ultraviolet measurements of the electron impact excitation of helium

Abstract: Total cross sections for the excitation of helium from its ground state to the 21P, 31P and 41P levels by electron impact have been measured in a polarization free manner using a crossed beam apparatus. The apparent excitation functions have been cascade corrected and made absolute using the optical oscillator strengths. The excitation functions exhibit shapes which differ from some other recent measurements particularly around the peak of the cross section curves. Agreement at high energies between the measured total cross section values and the Bethe approximation is verified within experimental error.

Théorie quantique des phénomènes de biréfringence electrique et magnétique des molécules

Abstract: A general formalism is set up to apply the variation-perturbation method to the quantum theory of non-linear optical effects, in particular to the electric and magnetic birefringence (Kerr and Cotton-Mouton effects). The quantities describing these effects are obtained from the wave function Ψ of the ground state of the unperturbed molecule and the different vectors and tensors which are determined by a variation method. With this method an approximate computation of the Kerr and Cotton-Mouton constants of some simple molecules has been made.

Theory of Surface Polarons

Abstract: We attempt to determine the binding energy and the wave function of the ground state of an electron that is attracted to the surface of an ionic crystal by its image potential and is repelled from the interior of the solid. For ionic crystals, such as LiF, the electrostatic theory is inadequate and the solid must be treated as a dynamical system. For shallow levels, the correction to the electrostatic approximation is small and behaves asymptotically as ${z}^{\ensuremath{-}3}$, where $z$ is the distance from the surface. The mass of a shallow electron is not enhanced. For deep levels the ground-state energy is calculated by a variational procedure in the limits of both weak and strong electron-phonon coupling. For the ground-state energy of an electron trapped on the LiF surface we find the value -0.29 eV. The mass of the deeply bound electron is enhanced.