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22 Jun 1995

Volume 102, Issue 24, pp. 9457-9745

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Electron paramagnetic resonance lineshape analysis of the photoexcited triplet state of C60 in frozen solution. Exchange narrowing and dynamic Jahn–Teller effect

Marina Bennati, Arthur Grupp, and Michael Mehring

J. Chem. Phys. 102, 9457 (1995); http://dx.doi.org/10.1063/1.468814 (8 pages) | Cited 10 times

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The EPR lineshape of the photoinduced triplet state of C60 in frozen toluene solution was studied by pulsed EPR spectroscopy. Lineshape calculations of the triplet spectra were performed including dynamical exchange effects. The observed spectra in a glassy matrix are compatible with zero field splitting parameters ‖D1‖ = 0.0114 cm−1 (12.2 mT) and ‖E1‖ = 0.0005 cm−1 (0.5 mT). The temperature dependence of the powder lineshape was simulated using a dynamical exchange model, where the triplet principal axis jumps between all equivalent sites allowed by the D5d symmetry for the lowest excited triplet state. The determined exchange rate turned out to be only weakly temperature dependent and suggests that the dynamic process is due to tunneling between Jahn–Teller distorted states rather than to real molecular jumps. In addition we have observed a different triplet state with zero field splitting parameters ‖D2‖ = 0.0100 cm−1 (10.6 mT), ‖E2‖ = 0.0015 cm−1 (1.6 mT) after annealing of the matrix. We attribute this to a C60 dimer or, alternatively, to crystal field effects. © 1995 American Institute of Physics.
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76.30.-v Electron paramagnetic resonance and relaxation
33.70.Jg Line and band widths, shapes, and shifts

Temperature dependence of the 14N quadrupole coupling constant of isocyanomethane

Thomas C. Stringfellow and Thomas C. Farrar

J. Chem. Phys. 102, 9465 (1995); http://dx.doi.org/10.1063/1.468815 (9 pages) | Cited 2 times

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We report NMR relaxation time measurements of the 14N quadrupole coupling parameter χN of isocyanomethane as a function of temperature in the solution‐state mixture of 6.4 mol %  H3CN ≡ C, 33.5 mol% d6‐ethylene glycol, and 60.1 mol % d6‐ethanol. We obtain values for the molecular correlation times using the T2/T1 method, which is a function only of the spectral density functions. The results demonstrate a significant, and approximately quadratic, temperature dependence of χN, which shows a minimum value of about 55 kHz at 222 K; the largest value measured was 125 kHz at 161 K. The results are compared with, and discussed within the context of, more traditional methods. The value of χN for neat isocyanomethane in the solid phase was measured to be 26.3 kHz. © 1995 American Institute of Physics.
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33.25.+k Nuclear resonance and relaxation
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Study on the hydration structure of L‐xylo and D‐arabo ascorbic acid solutions by time domain reflectometry

Toshihiro Umehara, Yasunori Tominaga, Akiko Hikida, and Satoru Mashimo

J. Chem. Phys. 102, 9474 (1995); http://dx.doi.org/10.1063/1.468816 (6 pages) | Cited 3 times

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The hydration structure of L‐xylo and D‐arabo ascorbic acids in aqueous solutions were investigated by a dielectric relaxation measurement over a wide frequency range from 10 MHz to 10 GHz from a standpoint on the difference of biological activity at 25 °C. In order to clarify the hydration structure the concentration dependence of dielectric relaxation was investigated not only in aqueous solution but in water–ethanol mixtures. Two kinds of dielectric relaxation processes were observed in each isomerism solution. The low frequency process is assigned to cooperative motions of ascorbic acid molecules and hydrated water. The high frequency process is assigned to reorientational motions of bulk water. From the results of the dehydration process out of the ascorbic acid surface by ethanol it is concluded that the amount of hydrated water of the L‐xylo ascorbic acid is more than that of the D‐arabo ascorbic acid. © 1995 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc.
87.15.Nn

Photoelectron spectroscopy of size‐selected transition metal clusters: Fe−n, n=3–24

Lai‐Sheng Wang, Han‐Song Cheng, and Jiawen Fan

J. Chem. Phys. 102, 9480 (1995); http://dx.doi.org/10.1063/1.468817 (14 pages) | Cited 158 times

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A higher resolution magnetic bottle photoelectron spectrometer for the study of the electronic structure of size‐selected metal clusters is presented. The initial study on Fe−n (n=3–24) is reported at a photon energy of 3.49 eV. The photoelectron spectra of these clusters exhibit sharp features throughout the size range. The spectra for Fe−3–8 show large size dependence with many resolved features. The spectra for Fe−9–15 exhibit some similarity with each other, all with a rather sharp feature near the threshold. An abrupt spectral change occurs at Fe−16, then again at Fe−19 and Fe−23. These photoelectron spectral changes coincide remarkably with changes of the cluster reactivity with H2. Extended Hückel molecular orbital (EHMO) calculations are performed for all the clusters to aid the spectral interpretations. The calculations yield surprisingly good agreement with the experiment for clusters beyond Fe9 when body‐centered cubic (bcc) structures are assumed for Fe9–15 and a similarly close‐packed structure with a bcc Fe15 core for the larger clusters. The EHMO calculations allow a systematic interpretation of the sharp photoelectron spectral features in Fe−9–15 and reproduced the abrupt spectral change taking place from Fe−15 to Fe−16. Most importantly, the reactivity changes of the clusters with H2 are successfully explained based on the detailed electronic structures of the clusters, as revealed from the photoelectron spectroscopy (PES) spectra and the theoretical calculations. The calculations also correctly predict the existence of magnetism in these clusters and yield reasonable values for the cluster magnetic moments. © 1995 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Jn Reactivity of clusters
61.46.-w Structure of nanoscale materials

High frequency (140 GHz) dynamic nuclear polarization: Polarization transfer to a solute in frozen aqueous solution

G. J. Gerfen, L. R. Becerra, D. A. Hall, R. G. Griffin, R. J. Temkin, and D. J. Singel

J. Chem. Phys. 102, 9494 (1995); http://dx.doi.org/10.1063/1.468818 (4 pages) | Cited 57 times

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Dynamic nuclear polarization (DNP) transfers the large polarization of unpaired electrons to nuclei and thus significantly enhances the signal strength in nuclear magnetic resonance (NMR) spectroscopy. High frequency/field (140 GHz/5 T) DNP has been implemented in solid state NMR experiments using a nitroxide radical as the paramagnetic polarizing agent in a water:glycerol frozen solution. The 1H and 13C NMR signal strengths of both the solvent and an amino acid solute have been enhanced by a factor of 185, which represents a reduction of ≳102 in sample size requirements or ≳104 in signal acquisition time. © 1995 American Institute of Physics.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
87.64.K- Spectroscopy
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization

Photoionization spectroscopy of the In–N2 van der Waals complex

L. R. Brock and M. A. Duncan

J. Chem. Phys. 102, 9498 (1995); http://dx.doi.org/10.1063/1.468819 (8 pages) | Cited 9 times

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A vibrationally resolved electronic spectrum is observed for the metal atom van der Waals complex In–N2. Two electronic band systems are detected with mass resolved two‐color photoionization spectroscopy. A lower energy system is observed slightly to the blue of the In ( 2D←P) atomic asymptote. It is characterized by a progression in the In–N2 stretching mode with a frequency of ω′e=76.7 cm−1. The higher energy system is slightly to the blue of the In (4P←2P) asymptote. It also exhibits a progression in the In–N2 stretch with a frequency of ω′e=87.7 cm−1. Extrapolation of the vibrational progressions leads to determination of the excited state dissociation energies. Energetic cycles based on the electronic transition energies, excited state dissociation energies, and atomic asymptotes lead to a determination of the ground state dissociation energy of D″0=1519 cm−1 (0.188 eV). A single‐photon photoionization experiment determines the ionization potential to be 43 372 cm−1 (5.377 eV). This IP value, together with the atomic IP and the ground state neutral dissociation energy, yields a dissociation energy of D″0=4817 cm−1 (0.597 eV) for the In+–N2 ion–molecule complex. © 1995 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.50.Gb Electronic excitation and ionization of molecules

Far‐infrared spectra and two‐dimensional potential energy surface for the ring‐bending and ring‐twisting vibrations of 5,6‐dihydro‐4H‐thiopyran

Jaebum Choo, N. T. Meinander, John R. Villarreal, and Jaan Laane

J. Chem. Phys. 102, 9506 (1995); http://dx.doi.org/10.1063/1.468820 (6 pages) | Cited 1 time

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5,6‐Dihydro‐4H‐thiopyran has been synthesized and its far‐infrared spectrum has been recorded. Eleven ring‐bending bands originating at 120.7 cm−1 and four ring‐twisting bands originating at 274.5 cm−1 were observed. Twelve sum and difference bands in the 383–397 and 148–166 cm−1 regions were also observed and these facilitated the construction of a detailed energy map including numerous excited vibrational states of the two coupled vibrations. The two‐dimensional potential energy surface, which satisfactorily fits the observed data, was determined to be V=9.48 ×104x4−4.13×104x2+1.37×104τ4−1.82×104τ2+1.10 ×105x2τ2, where x and τ are the bending and twisting coordinates, respectively. The minima on the potential energy surface correspond to twisting angles of ±48° (half‐chair conformation). The lowest energy bent (boat) conformation corresponds to a saddle point 1500 cm−1 above the twisted conformation on the potential energy surfaces, and the barrier to planarity was estimated to be 6000 cm−1. Both of these values have large uncertainties since the vibrational data only extend to 800 cm−1 above the potential surface minimum. The relatively low bending energy and high barrier to planarity can both be explained by the low force constant for the C–S–C angle bending. © 1995 American Institute of Physics.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
82.20.Kh Potential energy surfaces for chemical reactions

Main factors influencing the recoil energy distribution in the products of three‐atom reactions governed by long‐range forces and proceeding through long‐lived complexes

L. Bonnet and J. C. Rayez

J. Chem. Phys. 102, 9512 (1995); http://dx.doi.org/10.1063/1.468821 (10 pages) | Cited 6 times

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We propose a simplified version of the classical statistical theory of three‐atom reactions governed by long‐range forces. This version is based on a partial treatment of total angular momentum conservation. We focus the developments on the determination of the recoil energy distribution of reactions performed in supersonic crossed‐beam experiment. This distribution function is directly linked to the maximum values of the moduli of rotational and orbital angular momenta of the products consistent with their recoil energy and the total angular momentum disposal. Due to the simplicity of the present version, we can pinpoint the main factors which play a role in statistical reaction dynamics. It is shown that the shape of the translational energy distribution can be estimated essentially in terms of two mechanical parameters; the first one represents the available fraction of maximum angular momentum disposal in the products and the second gives a measure of the fraction of total angular momentum due to the rotation of the newly formed bond AB. Comparisons with exact calculations and experimental results are presented. They show that in addition to being able to determine propensity rules, our simple approach can even provide satisfying quantitative results. © 1995 American Institute of Physics.
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34.50.Lf Chemical reactions
82.20.Rp State to state energy transfer

Alignment probing of Rydberg states by stimulated emission

Eileen M. Spain, Mark J. Dalberth, Paul D. Kleiber, Stephen R. Leone, Stefan S. Op de Beek, and Jan P. J. Driessen

J. Chem. Phys. 102, 9522 (1995); http://dx.doi.org/10.1063/1.468767 (10 pages) | Cited 8 times

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The possibility of probing the collisions of aligned Rydberg atoms by stimulated emission is assessed with studies of a polarized state and a new measurement of a collisional alignment effect in atomic Ca. The stimulated emission method uses a laser to dump the desired state to a lower level which subsequently fluoresces. The technique can be used to obtain populations and polarization dependent information. First, the method is tested by applying it to an aligned Ca(4s17d 1D2) state. Alignment curves are measured when the initial state is prepared with both parallel and perpendicular relative polarizations. The experimentally observed alignment compares well with that derived from theoretical considerations of a saturated stimulated transition. Second, a two‐vector collisional alignment experiment (initial state and relative velocity vector) is performed to study the energy transfer process Ca(4s7d 1D2)+He→Ca(4s6f 1F3)+He+ΔE=17.7 cm−1, and alignment effects are measured by both stimulated emission and conventional direct fluorescence detection. A preference for the ‖m‖=1 and 2 initial states is observed in the relative cross sections. Essentially identical data are obtained with the two detection methods when elliptically polarized light is used for the stimulated emission detection method. The stimulated emission technique can provide alignment and population information of the final states, making it an excellent new tool for both three‐vector correlation experiments and state‐to‐state Rydberg transitions. © 1995 American Institute of Physics.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
34.50.-s Scattering of atoms and molecules

Orbital alignment cross sections by stimulated emission probing: The state‐to‐state Ca Rydberg process Ca(4s17d 1D2)+Xe→Ca(4s18p 1P1)+Xe

Eileen M. Spain, Mark J. Dalberth, Paul D. Kleiber, Stephen R. Leone, Stefan S. Op de Beek, and Jan P. J. Driessen

J. Chem. Phys. 102, 9532 (1995); http://dx.doi.org/10.1063/1.468768 (5 pages) | Cited 11 times

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The initial state alignment effect vs relative velocity is measured for a state‐to‐state Ca Rydberg collisional energy transfer process. The stimulated emission detection method is used to determine the alignment effect for the n,l‐changing transition: Ca(4s17d 1D2)+Xe→Ca(4s18p 1P1) +Xe+ΔE=−1.7 cm−1. The rate of electronic energy transfer in this state‐changing collision is observed to vary with the direction of the Rydberg electron charge cloud relative to the collision axis. Both the expected cos(4β) and cos(2β) dependencies are observed. The alignment data are analyzed to obtain the relative cross sections for the individual Ca(1D2) magnetic sublevels. The values of the m‐sublevel cross sections σ0:σ‖1‖:σ‖2‖ are 1.13±0.02:1.11±0.02:0.83±0.02. Qualitative interpretations of the relative cross sections in terms of both molecular (van der Waals) Born–Oppenheimer potentials and the impulse approximation are presented. © 1995 American Institute of Physics.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
34.50.-s Scattering of atoms and molecules
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Molecular dynamics of β‐carotene in solution by resonance enhanced optical Kerr effect

Marilena Ricci, Renato Torre, Paolo Foggi, Valey Kamalov, and Roberto Righini

J. Chem. Phys. 102, 9537 (1995); http://dx.doi.org/10.1063/1.468769 (7 pages) | Cited 2 times

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The orientational dynamics of β‐carotene in n‐alkane solutions is investigated by resonance enhanced optical Kerr effect. By use of this spectroscopic technique, it is possible to selectively investigate the relaxation of a probe molecule at a concentration level low enough to allow the observation of the averaged single‐molecule dynamics. For delay times longer than ∼20 ps all solutions show a single exponential decay, with a time constant depending on the viscosity, that is ascribed to the β‐carotene orientational relaxation. The dependence on viscosity of the measured relaxation times is compared with the predictions of different models. The purely hydrodynamic theories overestimate, by far, the solute effective volume and hence its orientational relaxation time; a much better agreement is obtained from two quasihydrodynamic models. © 1995 American Institute of Physics.
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33.15.Vb Correlation times in molecular dynamics
78.20.Ls Magneto-optical effects

State‐selected vibrational relaxation rates for highly vibrationally excited oxygen molecules

Ramón Hernández, Ralf Toumi, and David C. Clary

J. Chem. Phys. 102, 9544 (1995); http://dx.doi.org/10.1063/1.468770 (13 pages) | Cited 44 times

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The state‐selected vibrational relaxation rates in O2+O2 collisions, with one O2 molecule in a highly vibrationally excited state, have been calculated from first principles. The vibrationally close‐coupled, rotationally infinite order sudden approximation has been used to treat the collision dynamics and a potential energy surface based on high quality ab initio calculations, which include the variation of the O2 vibrational coordinates, has been developed. The calculated relaxation rates are in good agreement with those obtained from experiment for 8≤v<26 but fail to reproduce the sharp increase observed experimentally for v≥26 indicating the onset of a new vibrational relaxation mechanism. © 1995 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Light intensity effects on diffusion‐influenced fluorescence quenching in a hard‐sphere liquid: Molecular dynamics simulation and the many‐body Smoluchowski equation approach

T. Bandyopadhyay

J. Chem. Phys. 102, 9557 (1995); http://dx.doi.org/10.1063/1.468771 (8 pages) | Cited 5 times

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Molecular dynamics simulation of a model fluorescence quenching reaction A∗+B→B (A∗ is fluorophore and B is quencher molecule) in a hard‐sphere liquid where the fluorophore is excited for the first time or reexcited shortly after a bimolecular quenching process is carried out. The effects of light intensity on the temporal behavior of the fluorescence quenching kinetics is obtained by a summed form of an appropriate convolution integral using the simulation data. The convoluted results are compared with the recently developed general theoretical framework for the quenching kinetics where the exciting light pulse has a short but finite duration. The theory is based on hierarchy of phenomenological kinetic equations involving reactant molecule distribution functions. The alone effect of potential of mean force is examined and the radiation boundary condition is considered. Improvements over the simplest version of the Smoluchowski theory has been found. Considering the error introduced due to truncation of repeated excitation of A at the level of first repeated excitation (after a bimolecular process) the agreement between theory and simulation is excellent under certain limiting time profile of the exciting light pulse. © 1995 American Institute of Physics.
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33.50.Hv Radiationless transitions, quenching
31.15.xv Molecular dynamics and other numerical methods

Is slow thermal isomerization in viscous solvents understandable with the idea of frequency dependent friction?

Hitoshi Sumi and Tsutomu Asano

J. Chem. Phys. 102, 9565 (1995); http://dx.doi.org/10.1063/1.468772 (9 pages) | Cited 15 times

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Thermal Z/E isomerization of substituted azobenzenes and N‐benzylideneanilines takes place slowly after fast photoinduced E/Z isomerization. Its rate constant kobs is smaller than about 103 s−1 because of a high reaction barrier of about 50 kJ/mol. The pressure dependence of kobs measured in solvents as glycerol triacetate can well be understood in the framework of the transition state theory (TST) at low pressures. At high pressures, however, kobs begins to steeply decrease as the pressure increases, to be more exact, as the solvent viscosity η increases with the pressure, and the reaction enters the non‐TST regime. Since the η‐induced decrease of kobs at high pressures is slower than η−1, it cannot be described by the Kramers theory which regards the reaction as the barrier surmounting by Brownian motions regulated by frequency independent friction. Next, it was adjusted to the Grote–Hynes theory incorporating the idea of frequency dependent friction. The situation of kobs mentioned earlier enabled us to derive, without adjustable parameters, the correlation time τsc among random forces for friction due to solvent microscopic motions in the generalized Langevin equation on which the theory is based. At η∼107 Pa s, we obtained τsc∼1 ms. It is too long to justify the theory, since such a long‐time correlation cannot be realized among random forces exerting on the isomerizing moiety with an angstrom dimension. It will also be shown that τsc must be so long unphysically as to be at least much longer than 1 ps even if kobs at low pressures is adjusted to the theory. © 1995 American Institute of Physics.
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82.30.Qt Isomerization and rearrangement
82.20.Pm Rate constants, reaction cross sections, and activation energies
66.20.-d Viscosity of liquids; diffusive momentum transport

Rate expressions for excitation transfer. III. An ab initio study of electronic factors in excitation transfer and exciton resonance interactions

Gregory D. Scholes, Richard D. Harcourt, and Kenneth P. Ghiggino

J. Chem. Phys. 102, 9574 (1995); http://dx.doi.org/10.1063/1.468773 (8 pages) | Cited 41 times

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A detailed theory for electronic aspects of electronic excitation (energy) transfer (EET) for sandwich dimers was derived in paper II of this series [J. Chem. Phys. 101, 10 521 (1994)]. In II, the electronic transfer matrix element for EET was evaluated, then simplified to various levels of approximation. The results of ab initio molecular orbital calculations on an ethene sandwich dimer are reported here in order to test and quantify the theory of II. The calculations were undertaken using a STO‐6G basis set and localized molecular orbitals, with separations of 4, 5, and 6 Å between the molecules. It is demonstrated that the important electronic factors contributing to EET are the Coulombic interaction (for direct singlet–singlet transfer) and, for both singlet–singlet and triplet–triplet EET, orbital overlap‐dependent interactions. The dominant orbital overlap‐dependent terms arise from through‐configuration interaction, which involves successive one‐electron transfers mediated via bridging ionic configurations, first presented in II. The results confirm that the Dexter‐type exchange interaction is small in comparison. © 1995 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.vj Electron correlation calculations for atoms and ions: excited states

Orbital‐invariant second‐order many‐body perturbation theory on parallel computers: An approach for large molecules

David E. Bernholdt and Robert J. Harrison

J. Chem. Phys. 102, 9582 (1995); http://dx.doi.org/10.1063/1.468774 (8 pages) | Cited 20 times

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The equations for the second‐order many‐body perturbation theory [MBPT(2)] energy are derived in an orbital‐invariant representation, analogous to that obtained with the method of self‐consistent electron pairs of Meyer. This formulation is well suited to take advantage of the localized nature of interactions in large chemical systems in order to reduce the computational effort required to study them. This formulation of the MBPT(2) method also lends itself to implementation on parallel computers. We describe a scalable implementation in which the key data are distributed across the parallel computer rather than being replicated. Portability to both shared‐ and distributed‐memory computer architectures is provided through the use of a subroutine library implementing a ‘‘global array’’ programming model. We demonstrate that this approach is scalable even for relatively small chemical systems.
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36.20.-r Macromolecules and polymer molecules
31.15.xp Perturbation theory
31.15.xr Self-consistent-field methods

Linear dependencies among basis set products and near locality of some nonlocal operators

Douglas E. Hoch and John E. Harriman

J. Chem. Phys. 102, 9590 (1995); http://dx.doi.org/10.1063/1.468775 (8 pages) | Cited 10 times

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Linear dependencies among basis‐set products and the decomposition of the matrices of some one‐electron operators into local and nonlocal components have been investigated for several common quantum chemical basis sets and for a harmonic oscillator basis. For the first ten atoms and some simple diatomics, the kinetic energy, Fock, and density matrices were investigated. It was found that, for the basis sets used, these operators are all nearly local, in the sense that their matrices could be reproduced as the matrices of simple multiplicative‐function operators, even though there are significant numbers of linear dependencies among the products of the basis functions. SCF eigenfunctions for these systems were found to have no linear dependencies among products. Basis sets of one‐dimensional harmonic oscillator eigenfunctions were found to give a kinetic energy matrix that is not nearly local. © 1995 American Institute of Physics.
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31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods

Analytical energy gradients and geometry optimization in the divide‐and‐conquer method for large molecules

Qingsheng Zhao and Weitao Yang

J. Chem. Phys. 102, 9598 (1995); http://dx.doi.org/10.1063/1.468776 (6 pages) | Cited 37 times

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Based on the divide‐and‐conquer method in the density‐functional theory, an efficient approach is developed to compute analytically the energy gradients with respect to the nuclear coordinates. Tests performed show that both energy gradients and optimized molecular geometry converge to the corresponding results of the Kohn–Sham method when the nearest neighbor contributions are increased. © 1995 American Institute of Physics.
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36.20.-r Macromolecules and polymer molecules
31.15.E- Density-functional theory

Effective and intermediate Hamiltonians obtained by similarity transformations

Leszek Meissner and Marcel Nooijen

J. Chem. Phys. 102, 9604 (1995); http://dx.doi.org/10.1063/1.468777 (11 pages) | Cited 36 times

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A simple similarity transformation is used to derive equations for effective and intermediate Hamiltonians in a lucid way. Effective and intermediate Hamiltonians based on the wave operator formalism provide only a subset of all eigenvalues while the similarity transform technique divides the eigenvalue problem into two subproblems that can be solved separately. This means that the complete spectrum of the Hamiltonian remains well defined and this proves to be advantageous in the formal analysis and may be useful in many applications. Moreover both left and right hand eigenvectors of the transformed Hamiltonian can be obtained and this allows a convenient evaluation of properties. Rayleigh–Schrödinger and Brillouin–Wigner perturbation expansions of the intermediate Hamiltonians are discussed and a comparison is made of the various possible schemes. © 1995 American Institute of Physics.
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31.15.xp Perturbation theory
03.65.Ge Solutions of wave equations: bound states

Protonated hydrochlorous acid (HOClH+): Molecular structure, vibrational frequencies, and proton affinity

J. S. Francisco and S. P. Sander

J. Chem. Phys. 102, 9615 (1995); http://dx.doi.org/10.1063/1.468778 (4 pages) | Cited 2 times

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Protonated hydrochlorous acid (HOClH+) has been examined theoretically. Equilibrium geometries have been optimized and harmonic vibrational frequencies obtained for each of the parent and protonated structures at various levels of theory employing second‐order Møller–Plesset perturbation interaction theory (MP2), singles and doubles excitation configuration interaction theory (CISD), and coupled‐cluster theory (CCSD). Our study has found that protonation of the oxygen of HOCl is favored over protonation at the chlorine site. Protonation of the oxygen leads to a pyramidal structure of Cs symmetry. There is a planar Cs structure which is the inversion transition state. The inversion barrier is 3.2 kcal mol−1. The proton affinity of hypochlorous acid, HOCl, is found to be 153.1 kcal mol−1 at 0 K. © 1995 American Institute of Physics.  
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33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory

Coupled Hartree–Fock calculations of origin‐independent magnetic properties of benzene molecule

Paolo Lazzeretti, Massimo Malagoli, and Riccardo Zanasi

J. Chem. Phys. 102, 9619 (1995); http://dx.doi.org/10.1063/1.468779 (7 pages) | Cited 30 times

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Conventional coupled Hartree–Fock approach and two computational methods based on continuous transformation of origin for the electronic current density induced by a magnetic field have been employed to calculate magnetic susceptibilities and nuclear magnetic shieldings of carbon and hydrogen in benzene. Near Hartree–Fock estimates have been obtained by using a basis set of 492 gaugeless contracted Gaussians containing ad hoc polarization functions. Theoretical magnetic susceptibility and nuclear shieldings evaluated in the present work via pointwise coordinate transformation are independent of the origin of the reference system. A series of sum rules for gauge independence of computed results and charge‐current conservation has been tested to document the high accuracy of the calculation of magnetic properties. © 1995 American Institute of Physics.
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31.15.xr Self-consistent-field methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Electronic structure for the configurations ndk+1(n+1)s0(n+1)p1, ndk(n+1)s1(n+1)p1, and ndk−1(n+1)s2(n+1)p1 (k=1 to 10) in the first and second row of transition metals

J. M. García de la Vega

J. Chem. Phys. 102, 9626 (1995); http://dx.doi.org/10.1063/1.468780 (5 pages)

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Systematic numerical Hartree–Fock results for the lower states of the configurations ndk+1(n+1)s0(n+1)p1, ndk(n+1)s1(n+1)p1, and ndk−1(n+1)s2(n+1)p1 corresponding to the neutral atoms of the first and second row of transition metals are reported. Average energies of each configuration and LS energies of the corresponding lowest states are presented and discussed. The excitation energies and the relative orbital sizes for these states are also examined. © 1995 American Institute of Physics.
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31.15.xr Self-consistent-field methods

Ab initio molecular dynamics study of antimony clusters

V. Sundararajan and Vijay Kumar

J. Chem. Phys. 102, 9631 (1995); http://dx.doi.org/10.1063/1.468781 (7 pages) | Cited 4 times

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We present an ab initio molecular dynamics study of the atomic and electronic structure of SbN (N=2–8 and 12) clusters within the local density approximation and pseudopotential representation of the electron–ion interaction. Simulated annealing calculations have been done for 6‐, 7‐, 8‐, and 12‐atom clusters. While for Sb4 a bent rhombus is about 2 eV higher in energy than a regular tetrahedron, we find that it plays an important role in the structure of larger clusters. For Sb8 we obtain two weakly interacting tetrahedra to be of lowest energy. However, this is nearly degenerate with a bent rhombus interacting with a distorted tetrahedron. Further, our calculations suggest a bent rhombus based structure for Sb12 cluster indicating the observation of Sb4n clusters in Sb vapor condensation cell to be due to abundance of Sb4 clusters. A large gap is found to exist between the highest and the next occupied Kohn–Sham eigenvalues of the lowest energy isomers of 3‐, 5‐, and 7‐atom clusters. This is in agreement with the abundance of cations of these clusters in the laser ablation experiments. © 1995 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.E- Density-functional theory

Molecular theory of phase equilibria in model and real associated mixtures. II. Binary aqueous mixtures of inert gases and n‐alkanes

I. Nezbeda, J. Kolafa, J. Pavlíček, and W. R. Smith

J. Chem. Phys. 102, 9638 (1995); http://dx.doi.org/10.1063/1.468782 (9 pages) | Cited 10 times

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The phase equilibrium properties of a molecular‐based model of binary aqueous mixtures are investigated using an extended primitive model (EPW) for water, which incorporates a mean‐field attractive term in addition to the interactions given by the primitive model studied in part I of this series of papers. The second component, representing a nonpolar fluid, is modeled by a general hard body with a mean‐field attractive term. Analytical expressions for the Helmholtz free energy of this precisely defined molecular model are obtained from statistical mechanical theory, as a function of the molecular size, the mean‐field interaction term, and the shape of the second component. The predictions of our model are compared with the behavior of two classes of real aqueous mixtures: Group A={water+inert gases, hydrogen} and Group B={water+n‐alkanes}. The phase equilibrium properties are studied as a function of the ratio of the critical temperature τ and critical volume λ with respect to the corresponding quantities for water, and the global phase diagram (i.e., the type of phase behavior and its dependence on the model parameters) is determined. Since τ and λ are obtainable both from our theory and from experiment, our approach thus contains no adjustable parameters. The theory gives qualitatively correct predictions of the phase behavior of these two classes of mixtures, i.e., of the transition between Type IIIc and Type IIId critical line behavior in the Konynenberg and Scott classification scheme, of the presence or absence of pressure minima for Group B mixtures exhibiting Type IIIc behavior, and the dependence of the temperature and pressure of the Type IIIc temperature minimum on the size of the second‐component molecule. © 1995 American Institute of Physics.
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64.70.Ja Liquid-liquid transitions
64.75.-g Phase equilibria

The effect of phase separation on short‐ and intermediate‐range order in high‐silica Li2O–SiO2 glasses

A. J. G. Ellison, D. L. Price, J. E. Dickinson, and A. C. Hannon

J. Chem. Phys. 102, 9647 (1995); http://dx.doi.org/10.1063/1.468783 (6 pages) | Cited 2 times

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Wide‐angle neutron diffraction measurements have been performed on single‐phase and phase‐separated high‐silica glasses in the system Li2O–SiO2. The structure factors of the single‐phase glasses vary modestly with increasing Li2O concentration compared to the changes observed when Na2O or K2O is added to SiO2, and vestiges of the intermediate‐range order characteristic of v‐SiO2 are retained to 33 mol % Li2O. The structure factors of single‐phase and phase‐separated glasses are identical to within 1%–2%, indicating that phase separation results in very minor disruptions to local atomic arrangements. When combined with evidence obtained from previous studies, these data indicate that single‐phase high‐silica glasses in this system contain compositional heterogeneities analogous to those produced by phase separation. © 1995 American Institute of Physics.
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61.43.Fs Glasses
61.05.fm Neutron diffraction
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