Respective Ground States Research Articles

Plasma Line Emission during Single-Bubble Cavitation

Emission lines from transitions between high-energy states of noble-gas atoms (Ne, Ar, Kr, and Xe) and ions (Ar(+), Kr(+), and Xe(+)) formed and excited during single-bubble cavitation in sulfuric acid are reported. The excited states responsible for these emission lines range 8.3 eV (for Xe) to 37.1 eV (for Ar(+)) above the respective ground states. Observation of emission lines allows for identification of intracavity species responsible for light emission; the populated energy levels indicate the plasma generated during cavitation is comprised of highly energetic particles.

On the use of the MNDO-d semiempirical method for the structural study of chlorophyll b and anhydrous chlorophyll b dimer

Semiempirical MNDO-d molecular orbital calculations have been used for the structural study of chlorophyll b and anhydrous chlorophyll b dimer systems in their respective ground states. A model of chlorophyll b dimer has been considered whereby the magnesium atom is five-coordinate with an oxygen atom in the fifth coordination site. Total energies, net electric charges, and electronic dipole moments have been determined for the ground states of the above-mentioned molecules. The proposed models allow for the examination of distortions within the pyrroles and porphyrin macrocycles of these magnesium complexes. They also permit the estimate of changes in bond lengths, bond angles and dihedrals produced by dimerization via the acetyl oxygen of the carbometoxy group and the central magnesium atom, and changes in the π-electronic system of the chlorin systems. The results obtained are in good agreement with the experimental findings, and they reproduce many of the observed trends. In particular, neutron diffraction crystal structure, NMR and infrared spectra, provide experimental evidence in support of these theoretical predictions. Comparison with other theoretical results, shows that there is a good correlation between the DFT/B3LYP(6-31G*) and the MNDO-d, and also that the MNDO-d performs better than the HF/6-31G* and the PM5 in general.

Electron excitation coefficients and cross sections for excited levels of argon and xenon ions

In this paper, we present experimental results for the excitation coefficients of Ar+ and Xe+ ions to several excited states above their respective ground states. The data have been obtained from two different drift tubes and were analysed using Monte Carlo simulation, which involved an accurate representation of non-equilibrium effects and a complete set of initial cross sections. For some levels, it was possible to cover a sufficient range of E/N so that the electron energy dependent cross sections could be derived. For the remaining levels, normalization of the assumed shape of the cross sections could be performed by using excitation coefficients in a limited range of E/N. As expected, for all observed excited states, the cross section increases sharply from the threshold energy, reaches a maximum at about 40–50 eV and then decreases slowly for higher energies. The peak cross sections fall between 3 × 10−22 and 15 × 10−22 m2 for argon and between 3 × 10−22 and 21 × 10−22 m2 for xenon. The peak values of the cross sections are in reasonable agreement with the data previously obtained using the electron beam technique (binary collision), but the energy dependent profiles of the cross sections are significantly different. The absolute emission coefficients of three Xe2+ lines, excited from the ground state xenon atom, have also been deduced. They are about one order of magnitude smaller than those of the stronger Xe+ lines.

A theoretical study of the dications HeO2+ and He2O2+

Employing multireference CI techniques with correlation consistent basis sets, potential energy curves and surfaces for low-lying electronic states of HeO2+ and He2O2+ are computed. A detailed investigation of the structure and stability properties reveals that both molecular ions are metastable in their respective ground states, namely, 3Σ− for HeO2+ and for He2O2+. Calculating and analysing also potential energy curves of the singly charged diatomic system HeO+, a picture of He2O2+ emerges in which metastability in the triatomic dication is attributed to cooperative bonding of all three participating atomic subsystems.

Accurate relativistic many-body calculations of van der Waals coefficients C8 and C10 for alkali-metal dimers

We consider long-range interactions between two alkali-metal atoms in their respective ground states. We extend the previous relativistic many-body calculations of C6 dispersion coefficients [Phys. Rev. Lett. 82, 3589 (1999)] to higher-multipole coefficients C8 and C10. Special attention is paid to usually omitted contribution of core-excited states. We calculate this contribution within relativistic random-phase approximation and demonstrate that for heavy atoms core excitations contribute as much as 10% to the dispersion coefficients. We tabulate results for both homonuclear and heteronuclear dimers and estimate theoretical uncertainties. The estimated uncertainties for C8 coefficients range from 0.5% for Li2 to 4% for Cs2.

A constrained variational route to Pauling's electronegativity values†

Pauling's idea of estimating electronegativities of atoms by using bond-dissociation energy data and the idea of ionic-covalent resonance interaction are examined. Effective Hamiltonian for the perfectly covalent and perfectly ionic structures are defined and a constrained variational recipe to obtain their respective ground state energies suggested. These energies, together with the actual energy of the ground state of a diatom are used to obtain an estimate of the ionic-covalent interaction energy at different values of R. It naturally leads to an estimate of the electronegativity difference ΔX between the atoms at various distances.

Ab-initio calculations of the formation energies of BCC-based superlattices in the FeAl system

First-principles calculations of the total energies of A2 iron and aluminum, B2 (FeAl), B32 (FeAl) and D0 3 (Fe 3Al and FeAl 3) compounds were performed in the frame of density functional theory (DFT) using the Full Potential - Linear Augmented Plane Wave method (FP-LAPW). These results have been used to obtain formation energies of the respective ground states. The calculated formation energies of the D0 3 (Fe 3Al) and B2 (FeAl) compounds show excellent agreement with available calorimetric data on standard enthalpies of formation of FeAl alloys up to 50 at.% aluminum. As the FeAl system has a controversial magnetic behavior when described by ab-initio methods in the DFT, this agreement is remarkable.

Experimental and calculated molecular structures and high symmetry conformations of [Sb 2F 11] − (D 4h) and 1,4-C 4H 4N 2·2SbF 5 (D 2h)

Antimony(V) fluoride, SbF 5, forms a molecular adduct with pyrazine (1,4-diazine) of the composition 1,4-C 4H 4N 2·2SbF 5. Its molecular structure is obtained by single crystal X-ray diffraction. Crystal data of pyrazine·2SbF 5: orthorhombic, spacegroup Pbca (# 61); a=8.8052(8) Å; b=9.948(1) Å; c=12.297(2) Å; V=1077.1(2) Å 3; Z=4; T=173(1) K; R 1( I>3 σ( I))=0.031; wR 2=0.083. The Sb–F 4(eq) planes are eclipsed and the planar C 4H 4N 2 ring is at a 45° angle to give D 2h symmetry for pyrazine·2SbF 5. A very similar high symmetry conformation of pointgroup D 4h is found for the [Sb 2F 11] − anion in the metal carbonyl salts [Rh(CO) 4][Sb 2F 11], [Au(CO) 2][Sb 2F 11] and in [H 3F 2][Sb 2F 11]. Structural data for pyrazine·2SbF 5 and [Sb 2F 11] − from [H 3F 2][Sb 2F 11], as well as vibrational data for [Sb 2F 11] − (D 4h) are compared to calculated (DFT-B3LYP) data. According to the DFT calculations, the conformation for the [Sb 2F 11] − anion (D 4h) and pyrazine·2SbF 5 (D 2h) are both eclipsed with respect to the SbF 5-groups and eclipsed with respect to the pyrazine plane in pyrazine·2SbF 5 in their respective ground states.

Factors governing intrinsic chemical reactivity differences between clavulanic and penicillanic acids.

To help elucidate why penicillin-G is inactivated by certain bacterial beta-lactamase enzymes, whereas clavulanic acid (Clav, which is similar to penicillin-G except at positions 1, 2, and 6) inhibits beta-lactamase, the intrinsic chemical reactivities of these two antibiotics were assessed in this work. Ab initio and continuum dielectric methods were used to map out the gas-phase and solution-phase free-energy profiles for the alkaline hydrolyses of Clav and penicillanic acid (Peni, which is similar to penicillin-G except at position 6) as well as of a fictitious hybrid compound, Peni-db, which is similar to Clav and Peni except at positions 1 and 2, respectively. Furthermore, the ring strain energies of various lactam rings and the five-membered rings of Peni and Clav as well as their respective rate-limiting transition states were computed to assess the contribution of four- and five-membered ring strains to the antibiotic's activity. The predicted product distribution, rate-limiting step, and relative reaction rates for the alkaline hydrolysis of Peni and Clav are in accord with the experimental findings. The rate-limiting step in the alkaline hydrolysis of Peni, Clav, or Peni-db is the approach of the negatively charged hydroxide ion toward the anionic reactant to form a tetrahedral intermediate. The alkaline hydrolysis of Clav generates more stable products than that of Peni mainly because the O1 atom and the hydroxyethylidene group in Clav facilitate the opening of the five-membered ring; furthermore, the O1 atom can abstract a proton easier than the less polar S1 in Peni. Clav undergoes basic hydrolysis faster than Peni mainly because its hydroxyethylidene group leads to an increase in the positive charge on the carbonyl C7 atom, therefore enhancing favorable electrostatic interactions with the incoming hydroxide anion. To a lesser extent, the oxygen at position 1 in Clav also contributes to the rate acceleration because of the greater solvent stabilization of the oxygen-containing transition state as compared to the respective ground state. The inherent strain of the four-membered beta-lactam ring or five-membered ring does not enhance the alkaline hydrolyses of beta-lactam molecules such as Peni or Clav, consistent with the observation that the rate-limiting step does not involve a breakdown of the four-membered beta-lactam ring or five-membered thiazolidine/oxazolidine rings.

Confirmation of [formula omitted] and [formula omitted] ground states of Fe 2 and Fe 2− by CASSCF/MRCI

The ground states of Fe 2 and Fe 2 − are assigned to 9Σ − g and 8Σ − u , respectively, with r e=219 and 227 pm and ω e=303 and 255 cm −1 , respectively. The corresponding configurations 3d 134s 3 and 3d 134s 4 are those suggested for the respective ground states by Leopold et al. [J. Chem. Phys. 88 (1988) 3780] but ignored in all previous computational studies including two most recent density functional studies on first row transition metal dimers. The two bands of the photoelectron spectrum of Fe 2 − are assigned to the 9Σ g − and 7Σ g − states of Fe 2 with an energy difference of 0.48 eV.

Directed transport of an asymmetric particle pair induced by non-equilibrium conditions

The hopping motion of a classical bounded pair of two particles along a chain is investigated. It is shown that in the asymmetric case of the system dynamics including excited states which differ from the respective ground states by the barrier to be overcome by one of the two particles, the over- and underpopulation of these excited states leads to a directed motion of the particle pair. Thereby, overpopulation results in one direction of motion, whereas underpopulation results in the opposite direction, and the mean velocity is determined by the amount of over-resp. underpopulation. For small deviations from equilibrium, the system exhibits linear response well known from other ratchet-type models. Possible generalizations and applications are discussed.

Absolute photolysis cross-sections for NaHCO3 , NaOH, NaO, NaO2and NaO3 : implications for sodium chemistry in the upper mesosphere

The compounds NaHCO3, NaOH, NaO and NaO2 are formed from meteor-ablated Na in the upper mesosphere. This paper reports the absolute photolysis cross-sections of these species at selected wavelengths between 193 and 423 nm, measured by laser photofragment spectroscopy. The sodium species were produced in both a slow flow reactor and a fast flow tube, by the addition of appropriate reagents to a flow of atomic Na from a heat-pipe oven. The pulsed photolysis source was either a Raman-shifted excimer laser or a Nd:YAG laser, and the resulting Na atoms were probed by laser induced fluorescence at 589.0 nm (Na(3 2P3/2–2S1/2)). Measurements are reported at 200 and 300 K. A limited set of cross-sections for NaO3 was also obtained at 300 K. In the case of NaHCO3, NaOH and NaO, the onset of photolysis is close to the thermodynamic threshold calculated from quantum theory. Calculations using the CI-singles method predict excited states whose relative energies are in sensible accord with the bands in the experimental spectra, but which are too high in energy with respect to their respective ground states. Photodissociation coefficients are then derived which are appropriate for modelling sodium chemistry in the upper mesosphere. Photolysis of the major sodium reservoir species, NaHCO3, is shown to be an important route for recycling this compound, and is also predicted to produce the HCO3 radical, which should be stable under mesospheric conditions.

Spherical-deformed shape coexistence for thepfshell in the nuclear shell model

A spherical-deformed shape coexistence for semimagic pf-shell nuclei is investigated. Deformed states can arise by breaking the ${f}_{7/2}$ submagic shell, and coexist with spherical yrast states for ${}^{54}\mathrm{Fe}.$ These states are shown to be primarily two-particle two-hole excitations on top of the respective correlated ground states. In addition to these modes, a four-particle--four-hole excitation can be found for ${}^{54}\mathrm{Fe},$ which is related to the deformed band of doubly magic ${}^{56}\mathrm{Ni}.$ To investigate this shape coexistence, we use the conventional shell-model diagonalization, constrained Hartree-Fock, generator coordinate, variation-after-projection, and Monte Carlo shell-model methods.

Ab initio investigation on the valence and dipole-bound states of CNa − and SiNa −

CNa − and SiNa − have been studied by the CAS-ACPF method. The 3 Σ − ground states have binding energies of 5420 and 7517 cm −1, respectively. The 5 Σ − excited states are 494 and 1551 cm −1 above the respective ground states. The 1Δ , 3 Π , and 1 Π valence-excited states for SiNa − should be at least metastable. CNa − and SiNa − possess dipole-bound 5 Σ − and 3 Σ − states. Binding energies of these states in CNa − are 217 and 236 cm −1, respectively. SiNa − has two stable 5 Σ − dipole-bound states, whose binding energies are 246 and 118 cm −1, respectively.

Vh11/2bands in113Pdand115Pd

Two cascades of \ensuremath{\gamma} rays were discovered in ${}^{113}\mathrm{Pd}$ and ${}^{115}\mathrm{Pd}$ in prompt \ensuremath{\gamma}-ray spectroscopy with Gammasphere following heavy-ion induced fission in the reaction ${}^{18}{\mathrm{O}+}^{208}\mathrm{Pb}$ at 91 MeV. Comparison with recently observed band structures in ${}^{109}\mathrm{Pd}$ and ${}^{111}\mathrm{Pd}$ as well as blocking arguments lead to an interpretation of these bands as $\ensuremath{\nu}{h}_{11/2}$ bands. This discovery, together with cranked Woods-Saxon and total Routhian surface calculations, indicates that increased rotational frequency stabilizes a prolate but still \ensuremath{\gamma}-soft shape in the neutron-rich, even-even Pd isotopes up to ${}^{116}\mathrm{Pd},$ which exhibit very \ensuremath{\gamma}-soft nuclear potentials in their respective ground states.

Electron impact single ionization of multiply charged iron ions

Employing the animated crossed-beams technique, absolute cross sections for electron impact single ionization of the iron isonuclear sequence are measured for charge states q = 1-6 for electron energies from threshold up to 1 keV, as well as for the intermediate charge states q = 9,10 up to an electron energy of 5 keV. The cross sections observed for Feq+ ions in charge states q = 1 - 4, 9 and 10 show a significant ionization signal below the respective ground state threshold resulting from ions in excited, long-lived metastable states in the parent ion beam. In the case of Fe5+ and Fe6+ no metastable components are found. The experimental results are in good agreement with the theoretical predictions if excitation-autoionization processes are taken into account. Our measured cross sections are also in good agreement with experimental results of other groups.

Cold-fission modes in [sup 252]Cf

The binary and ternary cold fragmentations of heavy nuclei are studied in the framework of a deformation-dependent cluster model in which the final fragments are produced in their respective ground states and interact via a double-folded potential with M3Y forces. The deformation effects are taken into account up to multipolarity λ=4. It is shown that two regions of cold fragmentation arise. The first one has large quadrupole and even hexadecapole deformations and mass number of the heavy fragment ranging between 138 and 158. In the second region, the Q-value principle dictates the occurrence of a few spherical nuclei around the doubly magic nucleus 132 Sn , which is similar to the case of heavy-cluster radioactivity, where the daughter nuclei are around 208 Pb . This structure is similar for binary and ternary cold fission. The cold-fission yields are computed for the binary fragmentation and for the alpha-accompanied fission of 252 Cf . For the ternary cold-fission mode we derive the most likely geometrical and dynamical characteristics of the fragments at the moment of release of the light particle and perform classical trajectory calculations, in order to compute the final kinetic energy of the alpha particle. The recent observation of 10 Be in cold ternary fission is discussed in connection with the concept of a giant nuclear molecule.

Bromine Halides: The Neutral Molecules BrClFn (n = 1− 5) and Their Anions Structures, Energetics, and Electron Affinities

Density functional methods were used for predictions of the structures and energetics of molecules and anions in the series BrClFn (n = 1−5). Very little is known from experiment about these potentially important interhalogen molecules. Energy minima were found for all neutral molecules with the exception of BrClF5. However, the dissociation limits for ClF elimination from the BrClF3 (BHLYP and B3LYP only) and BrClF4 (all methods) molecules lie below the energy of the respective ground states. All the BrClFn anions are bound with respect to the corresponding neutrals; energy minima were found for anions up to BrClF5-. Structures of isomers with the chlorine atom in the central position were also optimized. However, these local minima lie substantially above the bromine-centered structures, and the energy gap between isomers grows with n. For the neutral molecules two paths of dissociation were found to possess the lowest energies, i.e., chlorine atom and ClF elimination. The latter channel becomes predominant at n > 1. For the anions the lowest energy dissociation pathways are Cl- or Cl elimination, but for n = 3, 5, ClF elimination becomes predominant. The adiabatic electron affinities, the vertical electron affinities of the BrClFn molecules, and the vertical detachment energies of the BrClFn- anions were predicted in this work. The adiabatic electron affinities of the closed-shell BrClFn molecules significantly exceed those of the corresponding BrFn species, while for molecules with an odd number of electrons they are similar or slightly lower than electron affinities in the BrFn series. Many new experiments are suggested by this researcher, in light of the large predicted electron affinities and the fact that none of these has been measured in the laboratory.

Pairwise contact potentials are unsuitable for protein folding

We demonstrate that pairwise contact potentials alone cannot be used to predict the native fold of a protein. Ideally, one would hope that a universal energy function exists, for which the native folds of all proteins are the respective ground states. Here we pose a much more restricted question: Is it possible to find a set of contact parameters for which the energy of the native contact map of a single protein (crambin) is lower than that of all possible physically realizable decoy maps? The set of maps we used was derived by energy minimization (not by threading). We seek such a set of parameters by perceptron learning, a procedure which is guaranteed to find such a set if it exists. We found that it is impossible to fine-tune contact parameters that will assign all alternative conformations higher energy than that of the native map. This finding proves that there is no pairwise contact potential that can be used to fold any given protein. Inclusion of additional energy terms, such as hydrophobic (solvation), hydrogen bond, or multibody interactions may help to attain foldability within specific structural families.

Laser spectroscopic measurements of binding energies and fine-structure splittings ofCo−,Ni−,Rh−,andPd−

A tunable infrared laser source is utilized to study the photodetachment threshold spectra of the transition-metal negative ions ${\mathrm{Co}}^{\ensuremath{-}},$ ${\mathrm{Ni}}^{\ensuremath{-}},$ ${\mathrm{Rh}}^{\ensuremath{-}},$ and ${\mathrm{Pd}}^{\ensuremath{-}}.$ The binding energies of the respective ionic ground states are found to be 663.3(6), 1157.16(12), 1142.89(20), and 562.14(12) meV. In addition, a ${}^{3}{F}_{4}{\ensuremath{-}}^{3}{F}_{3}$ fine-structure splitting of 875(15) ${\mathrm{cm}}^{\ensuremath{-}1}$ is measured for ${\mathrm{Co}}^{\ensuremath{-}},$ and the ${}^{2}{D}_{5/2}{\ensuremath{-}}^{2}{D}_{3/2}$ splitting of ${\mathrm{Ni}}^{\ensuremath{-}}$ is determined to be 1485(3) ${\mathrm{cm}}^{\ensuremath{-}1}.$ For ${\mathrm{Pd}}^{\ensuremath{-}}$, the electronically excited ${4d}^{9}{5s}^{2}{}^{2}{D}_{5/2}$ state is found to lie 1127(4) ${\mathrm{cm}}^{\ensuremath{-}1}$ above the ${4d}^{10}{5s}^{2}{S}_{1/2}$ ionic ground state, i.e., it is bound by 422.4(5) meV. The results agree with previous values obtained from laser photodetached electron spectra, but constitute improvements in accuracy of up to two orders of magnitude.