bluuebunny/crossref_metadata_2025 huggingface dataset:
Hole density dependence of effective mass, mobility and transport time in strained Ge channel modulation-doped heterostructures
Authors: Irisawa T. , Myronov M. , Mironov O. A. , Parker E. H. C. , Nakagawa K. , Murata M. , Koh S. , Shiraki Y.
Published: February 2003

We performed systematic low-temperature (T=350 mK–15 K) magnetotransport measurements on the two-dimensional hole gas with various sheet carrier densities Ps=(0.57–2.1)×1012 cm−2 formed in the strained Ge channel modulation-doped (MOD) SiGe heterostructures grown on Si substrates. It was found that the effective hole mass deduced by temperature dependent Shubnikov–de Hass oscillations increased monotonically from (0.087±0.05)m0 to (0.19±0.01)m0 with the increase of Ps, showing large band nonparabolicity in strained Ge. In contrast to this result, the increase of the mobility with increasing Ps (up to 29 000 cm2/V s) was observed, suggesting that Coulomb scattering played a dominant role in the transport of the Ge channel at low temperatures. In addition, the Dingle ratio of the transport time to the quantum lifetime was found to increase with increasing Ps, which was attributed to the increase of remote impurity scattering with the increase of the doping concentration in MOD SiGe layers.
Band offsets at CdCr2Se4–(AlGa)As and CdCr2Se4–ZnSe interfaces
Authors: Zhao H. B. , Ren Y. H. , Sun B. , Lüpke G. , Hanbicki A. T. , Jonker B. T.
Published: February 2003

The band discontinuities of CdCr2Se4–(AlGa)As and CdCr2Se4–ZnSe heterojunctions are measured to high resolution by internal photoemission using a widely tunable optical parametric amplifier system. The conduction band offsets ΔEc=660 and 530 meV at the CdCr2Se4–GaAs and CdCr2Se4–ZnSe interfaces are determined from the threshold energies of the photocurrent spectrum at room temperature.
Fabrication of Zn/ZnS nanocable heterostructures by thermal reduction/sulfidation
Authors: Li Quan , Wang Chunrui
Published: February 2003

Single-crystalline Zn/ZnS coaxial nanocables were fabricated through thermal reduction of ZnS using graphite powder at elevated temperatures. Energy dispersive x-ray analysis of the as-fabricated samples indicated that the nanowires were composed of Zn and S only. Transmission-electron-microscopic study of the nanowires revealed that they had core/sheath contrast, suggesting a Zn core/ZnS sheath heterostructure. Epitaxial relationship was observed between the Zn and the ZnS. The possible formation mechanisms of such nanocables are discussed.
Electrical characteristics of proton-irradiated Sc2O3 passivated AlGaN/GaN high electron mobility transistors
Authors: Luo B. , Kim Jihyun , Ren F. , Gillespie J. K. , Fitch R. C. , Sewell J. , Dettmer R. , Via G. D. , Crespo A. , Jenkins T. J. , Gila B. P. , Onstine A. H. , Allums K. K. , Abernathy C. R. , Pearton S. J. , Dwivedi R. , Fogarty T. N. , Wilkins R.
Published: February 2003

Sc 2 O 3 -passivated AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated with 40 MeV protons to a fluence corresponding to approximately 10 years in low-earth orbit (5×109 cm−2). Devices with an AlGaN cap layer showed less degradation in dc characteristics than comparable GaN-cap devices, consistent with differences in average band energy. The changes in device performance could be attributed completely to bulk trapping effects, demonstrating that the effectiveness of the Sc2O3 layers in passivating surface states in the drain-source region was undiminished by the proton irradiation. Sc2O3-passivated AlGaN/HEMTs appear to be attractive candidates for space and terrestrial applications where resistance to high fluxes of ionizing radiation is a criteria.
ESR–ENDOR study of x-irradiated α-methyl-D-glucopyranoside single crystals at 12 K: Influence of hydrogen bonding on primary alcohol group radiation chemistry
Authors: Madden K. P. , Bernhard W. A.
Published: February 2003

Single crystals of α-methyl-D-glucopyranoside x-irradiated at 12 K contain a primary alkoxy radical. In contrast to the previously characterized primary alkoxy radical found at 77 K, the C–O bond does not significantly reorient. This result, as well as deprotonation of an accompanying primary hydroxyalkyl radical, is explained by the presence of three, instead of the usual two, hydrogen bonds about the O6 atom.
An isothermal–isobaric computer simulation of the supercooled-liquid/glass transition region: Is the short-range order in the amorphous solid fcc?
Authors: Abraham Farid F.
Published: February 2003

[N,P,T] Monte Carlo simulations of metastable supercooled-liquid and amorphous phases of Lennard-Jones atoms indicate several distinct signatures for identifying the glass transition boundary; i.e., the density, enthalpy, and pair distribution function dependences on temperature and pressure are different for the two phases. The effective hard-sphere packing fraction ηa at the glass transition boundary is verified to be the same whether the glass is prepared by temperature quenching or pressure crushing. Using ηa and liquid-state perturbation theory, the glass transition boundary is calculated for the metastable pressure–temperature phase diagram of the Lennard-Jones system. Finally, we argue that the evolution of the PDF structure as a function of degree of metastability suggests that the amorphous phase is a ’’distorted fcc packing.’’ A comparison with experiment is made.
Molecular librations and the α–γ phase transition in solid nitrogen based on the Kihara potential
Authors: Kobashi Koji , Kihara Taro
Published: February 2003

Properties of solid N2 under pressure have been studied in terms of the Kihara potential consisting of the 6–12 core–core interaction and the electrostatic quadrupole–quadrupole interaction. The observed P–V data, the α–γ phase transition, and the libration frequencies were reproduced satisfactorily in terms of slightly different potential parameter sets for α and γ–N2. It was concluded that in order to reproduce the α–γ phase transition, the molecular shape represented by the electron charge density contour of 0.002 a.u. should be taken into account in the empirical potentials.
Molecular Rydberg transitions. XVI. MCD of CH3Br
Authors: McGlynn S. P. , Scott J. D. , Felps W. S. , Findley G. L.
Published: February 2003

Magnetic circular dichroism, first derivative (of absorption), and absorption spectra of methyl bromide are presented for the first s–Rydberg transition region, 55 000–61 000 cm−1. A straightforward analysis in terms of the ratios (MCD/derivative) of the signal amplitudes yields a unique identification of the first s–Rydberg states, 3E(1) and 1E(1). These identifications, in conjunction with oscillator strength ratios and an intermediate coupling model, lead to an assignment of the remaining first s–Rydberg states 3E(2) and 3E(0±). All of these assignments are corroborative of ones based on vibrational analyses and extrapolations [S. Felps, P. Hochmann, P. Brint, and S. P. McGlynn, J. Mol. Spectrosc. 59, 355 (1976)]. The power of MCD techniques in VUV Rydberg analyses is strikingly demonstrated.
Analysis of the ’’charge resonance’’ transition in anthracene dimer anion
Authors: McHale Jeanne , Simons Jack
Published: February 2003

The experimentally observed ’’charge resonance’’ transition of anthracene dimer anion is explained in terms of the resonance interaction of the lowest unoccupied orbitals of neighboring anthracene molecules. The distortion energies of the anthracene molecule and anion are shown to make an important contribution to the excitation energy. The numerical estimate of the resonance integral, based on the experimental absorption energy of the dimer anion, is shown to be related to that which is appropriate for a calculation of electron mobility in crystalline anthracene.
Chemiluminescence of argon bromide. II. Potential curves of ArBr and population distributions in the B (1/2) and C (3/2) electronic states
Authors: Golde Michael F. , Kvaran Agust
Published: February 2003

The continuous emission spectra of ArBr (Paper I) are analyzed by comparison with computer simulations, using trial molecular potential curves and uniform WKB wave functions. Vibrational distributions in the emitting states are derived by a least-squares technique. For the highly-structured B (1/2)−X (1/2) continuum, rather precise results are obtained and it is shown that the product energy distributions in the reactions Ar+HBr and K+HBr are closely similar. Analogus simulations of the C (3/2)−A (3/2) system yield less precise information because this continuum is partially overlapped by B−X emission. The results for both systems support previous ab initio calculations of the noble-gas halides.
Quasielastic light scattering from solutions in the small wave vector limit
Authors: Weissman Michael B.
Published: February 2003

An expression for the mutual diffusion coefficient of a solute consistent with irreversible thermodynamics is compared with expressions obtained by other methods. The results of experiments on protein solutions and nearly ordered bead solutions are compared with theory. It is argued that for small wave vectors the bead experiments are dominated by effects of polydispersity.
Quantum statistical theory of flash desorption
Authors: Gortel Z. W. , Kreuzer H. J. , Spaner D.
Published: February 2003

The nonequilibrium initial value problem of phonon-mediated flash desorption of a gas from a solid surface is formulated explicitly and flash desorption times td=td(Tg, Ts) are calculated, using a nonlocal separable surface potential, as a function of both initial and final temperatures Tg and Ts, respectively. We find that for fixed Tg, td can be approximated by Frenkel’s formula over a limited range of flash temperatures Ts. We fit our theory to flash desorption data for He desorbing from Constantan and find excellent agreement. Predictions on 4He (H or D) desorbing from LiF (NaF) are given. Our theory is formulated both in one and three dimensions and it is shown by numerical examples that the theory of flash desorption works equally well in either case.
Radial distribution function of random coil polymers
Authors: Koyama Ryuzo
Published: February 2003

Assuming a Gaussian-form intermolecular potential between random coil polymers, the radial distribution function of these molecules is calculated from the Yvon–Born–Green integral equation with an approximation better than the previous paper [J. Phys. Soc. Jpn. 43, 287 (1977)]. The excess intermolecular potential [denoted by w(r) in the text] is derived in a more general form than the Gaussian function assumed previously. But the results of the radial distribution function of both the reports show the same qualitative properties; the value of this function for small molecular distance is smaller or larger than unity depending on whether the polymer interaction is repulsive or attractive. And this value increases with polymer concentrtion, particularly for repulsive interaction, this value tends to unity in the entire range of molecular distance when the concentration increases very largely.
Resonance peak shapes in molecular photoionization mass spectroscopy
Authors: Eland J. H. D. , Berkowitz J. , Monahan J. E.
Published: February 2003

Some autoionizing resonances are observed in different fragment ion channels with different shapes and peak positions. It is shown that a simple parametrization yields consistent resonance energies and widths independent of the channel and that peak shapes vary systematically with the relative intensity of the resonance and the continuum in the channel observed.
Two large-amplitude motions in triatomic molecules. Force field of the 1B2 (1A′) state of SO2
Authors: Mezey Paul G. , Ramachandra Rao Ch. V. S.
Published: February 2003

A program has been developed to calculate the energy levels associated with the two large-amplitude stretching vibrations ν1 and ν3 of a bent triatomic molecule in which the ν3 oscillation occurs in a double minimum potential. Employing the two large-amplitude Hamiltonian H0s(ρ1,ρ3) obtained earlier by Brand and Rao. [J. Mol. Spectrosc., 61, 360 (1976)], the vibrational energy levels (v1,v3even/odd) of SO2 molecule in its 1B2 (1A′) excited state are calculated. The nine parameters of the potential function V0(ρ1,ρ3) are then adjusted to give a least-square fit to the 12 observed vibrational term values corresponding to the levels (v1,v3even) of S16O2 and S18O2. A three-dimensional picture of the potential surface V0(ρ1,ρ3) using the final set of force constants is also presented. The saddle point of this surface is at (ρO1=1.5525 Å, ρO3=0.0 Å) and the absolute minima occur at (ρe1=1.5644 Å, ρe3=±0.0745 Å). Barrier height, i.e., the height of the saddle point above the absolute minima, is 140 cm−1.
Rotational relaxation in sonic nozzle expansions
Authors: Klots Cornelius E.
Published: February 2003

The thermal conduction model for cooling in sonic nozzle expansions is extended to rotational degrees of freedom. Unimolecular decomposition theory, as applied to collision complexes, provides a natural formalism for describing the rotational–translational coupling. Simple expressions are presented for the terminal ’’temperatures’’ as functions of the source parameters and the relevant long-range r−6 potential. Extensions to other potentials and to vibrational relaxation are indicated.
Emission spectra of alkyl substituted diacetylene radical cations: CH3–C≡C–C≡C–R+ with R=H, D, CH3, and CD3; CD3–C≡C–C≡C–R+ with R=H, D, CD3 and C2H5–C≡C–C≡C–R+ with R=H and C2H5. Competition of the radiative Ã (π−1) → X̃ (π−1) and fragmentation decay of their Ã (π−1) states
Authors: Maier John P. , Marthaler Oskar , Kloster-Jensen Else
Published: February 2003

Optical emission spectra of the radical cations given in the title have been detected in the gaseous phase, using low energy electrons for the excitation. The band systems are assigned to the Ã (π−1) →X̃ (π−1) electronic transitions of these cations by reference to the photoelectron spectroscopic data. A vibrational analysis of the emission bands yields the frequencies of some of the totally symmetric fundamentals for the X̃ states and of one or two for the Ã states that are supplemented by the frequencies inferred from the photoelectron spectra. The title cations excited to their Ã states exhibit the rare decay behavior in that the radiative relaxation is detected even though fragmentation also takes place. The lifetimes of these cations in the lowest vibrational levels of the Ã states have been measured. The rates of the radiative and radiationless processes depleting the Ã states are estimated from these lifetimes and the upper limits of the quantum yields of emission obtained from the cation breakdown curves. Also reported are some other alkyl diacetylene cations for which the radiative pathways could not be detected.
Photoexcitation and ionization in molecular oxygen: Theoretical studies of electronic transitions in the discrete and continuous spectral intervals
Authors: Gerwer A. , Asaro C. , McKoy B. V. , Langhoff P. W.
Published: February 2003

Theoretical studies of valence-electron (1πg, 1πu, 3σg) photoexcitation and ionization cross sections in molecular oxygen are reported employing separated-channel static-exchange calculations and the Stieltjes–Tchebycheff moment-theory technique. As in previously reported investigations of photoexcitation and ionization in small molecules following this approach, canonical Hartree–Fock orbitals, large Gaussian basis sets, and many-electron eigenstates of correct symmetry are used in defining appropriate noncentral static-exchange potentials and in computations of the appropriate discrete and continuum transition strengths. It is particularly important in molecular oxygen to incorporate the appropriate ionic parentages of the various photoionization multiplet states in order to obtain the correct partial-channel cross sections. The calculated discrete series associated with 1πg excitation are found to be in good agreement with available experimental assignments and previously reported theoretical studies, and the predicted states associated with 1πu and 3σg excitations are in general accord with assignments for the higher series based on spectral and quantum-defect analysis. Although the observed photoelectron spectra and photoionization cross sections are relatively complex, the calculated total vertical electronic photoabsorption cross section and the partial-channel photoionization cross sections for production of X 2πg, a 4πu, A 2πu, 2 2πu, 3 3Πu, b 4Σg−, and B 2Σg− ionic states are found to be in good accord with recent synchrotron radiation, line-source, electron-impact, and (e,2e) dipole oscillator-strength measurements when proper account is taken of the parentages of the various multiplet states. The partial-channel cross sections exhibit resonancelike structures that can be attributed to contributions from diabatic valencelike virtual states that appear in the appropriate photoionization continua, rather that in the corresponding discrete spectral intervals. These features in the dipole spectrum of molecular oxygen are discussed and are contrasted and compared with the results of previously reported related studies in molecular nitrogen and carbon monoxide.
A discrete scattering series representation for lattice embedded models of chain cyclization
Authors: Fraser Simon J. , Winnik Mitchell A.
Published: February 2003

In this paper we develop a lattice based model of chain cyclization in the presence of a set of occupied sites V in the lattice. We show that within the approximation of a Markovian chain propagator the effect of V on the partition function for the system can be written as a time-ordered exponential series in which V behaves like a scattering potential and chainlength is the timelike parameter. The discrete and finite nature of this model allows us to obtain rigorous upper and lower bounds to the series limit. We adapt these formulas to calculation of the partition functions and cyclization probabilities of terminally and globally cyclizing chains. Two classes of cyclization are considered: in the first model the target set H may be visited repeatedly (the Markovian model); in the second case vertices in H may be visited at most once(the non-Markovian or taboo model). This formulation depends on two fundamental combinatorial structures, namely the inclusion–exclusion principle and the set of subsets of a set. We have tried to interpret these abstract structures with physical analogies throughout the paper.
An integral equation approach to scaled 1/Z-expansions of Hartree–Fock energies
Authors: McDowell Keith
Published: February 2003

A resummation of certain single-excitation perturbation diagrams occurring in a scaled 1/Z-expansion of atomic Hartree–Fock energies is accomplished by introducing a new integral equation. To test the new procedure, calculations are carried out on the atomic two-electron isoelectronic sequence. It is found that the resulting approximate Hartree–Fock energy appears to be an upper bound to the exact energy. Agreement with previous accurate results to within 10−6 a.u. is obtained with the exception of the H− ion. Here the agreement is within 10−4 a.u.
Influence of bounded trajectories in the study of binary time correlation functions
Authors: Bonamy L. , Hoang N. M.
Published: February 2003

In the frame of binary collisions, it is shown that in addition to the well known unbounded trajectories, the bounded trajectories may contribute significantly to the calculation of time correlation functions. The relative influences of the different contributions is strongly temperature dependent. An illustration is made in the case of the radial distribution function g (r). Moreover, it is shown that under specific conditions, the unbounded contribution must be taken into account in the study of the temperature dependence of linewidths.
Influence of the finite duration of collisions on the infrared line shape
Authors: Boulet C. , Robert D. , Galatry L.
Published: February 2003

The influence of the finite duration of the collisions is analyzed for the pure rotational lines of a diatom–atom gas mixture and discussed vs the general trends of the anisotropic part of the intermolecular potential. The calculated line profiles, using curved classical trajectories and including all the orders of the interaction in the description of the time evolution of the dipole moment, show a significant deviation from the usual impact van Vleck–Weisskopf profiles as soon as the anisotropic potential exhibits a marked well. Such a deviation is consistent with the experimental results of Frenkel and van der Elsken for HCl–Ar mixture. At last, the shape of the rotational lines in the harmonic 0–2 vibrational band of HCl perturbed by xenon is calculated. In that case, the presence of a strong vibrational dephasing effect increases the influence of the finite duration of collisions and introduces a marked asymetry of the line shape.
Two-photon excitation as a monitoring technique for photodissociation dynamics: CF3NO→CF3+NO(v,J)
Authors: Asscher M. , Haas Y. , Roellig M. P. , Houston P. L.
Published: February 2003

Two pulsed dye lasers each pumped by a separate Nd:YAG laser were used to study the vibrational and rotational states of NO. (AIP)
Raman study of vibrational broadening in C4F8 in the dense fluid region
Authors: Jonas J. , Perry S. , Schroeder J.
Published: February 2003

The temperature and density dependence of the line width of the 698 cm−1 line in the Raman spectrum of CuF8 has been determined experimentally. The line width behaviour is interpreted in terms of models for vibrational dephasing of the molecule. (AIP)
The effect of intermolecular potential well depths on vibrational energy transfer
Authors: Gordon Robert J.
Published: February 2003

It is contended that under certain circumstances the vibrational energy transfer in the ground electronic state of molecules is given by parmenters relation1−3 P (T) =C exp (EkT) where C is a constant and and E is related to potential well depth. (AIP)
Finer examination of Politzer’s improved approximate energy formula for molecules
Authors: Anno Tosinobu
Published: February 2003

Politzer’s relation1,2 connecting the total energy E of a molecule with the total electrostatic potential VO,A at the nucleus of A within the molecule is given by: E=ΣA kA ZA VO,A. It is argued that changes in KA due to change of the nuclear environmental of A should be taken into accounts to get an accurate value of E. (AIP)
Long time dynamics of swollen rubbers: Optical and mechanical properties
Authors: Ronca G.
Published: February 2003

The low frequency dynamics of a swollen network is investigated by means of a many-body Langevin equation which treats the junctions like slowly moving structural units, as suggested by recent improvements of the equilibrium theory of rubber elasticity. Both the viscoelastic constitutive equation and the optical autocorrelation function S (k, t) of a junction-labeled network are then calculated for a model system with very long circuits. Deviations of S (k, t) from exponential behavior and quadratic linewidth are predicted to occur if the scattering wavelength is not much larger than the average distance between adjacent crosslinks. Calculated deviations are shown to be strongly dependent on functionality and swelling ratio. In particular, we predict a remarkable difference between trifunctional and tetrafunctional networks.
Production and properties of S(1S) in liquid argon (88 °K) and nitrogen (77 °K)
Authors: Black G. , Sharpless R. L. , Lorents D. C.
Published: February 2003

Photodissociation of OCS to produce S(1S) has been observed in both liquid argon and liquid nitrogen over the wavelength range 144 to 161 nm. Over this wavelength range, the quantum yields are within a factor of 2 of those previously measured in the gas phase. Spectra of the emissions have been measured. The emissions have radiative lifetimes of (39±2) μsec in liquid argon and (50±3) μsec in liquid nitrogen. Evidence is presented that S(1S) exists mainly as bound molecules in these media and that the lifetimes measured are those for the bound 2 1Σ+−1 1Σ+ transitions. In these media the quenching of the emission by OCS has a rate coefficient of (4±1) ×10−14 cm3 molecule−1 sec−1.
19F spin-rotation tensors in CCl3F and ClO3F and their application to liquid-phase rotational diffusion
Authors: Garg S. K. , Ripmeester J. A. , Davidson D. W.
Published: February 2003

Shielding anisotropies of 19F nuclei in CCl3F and ClO3F of Δσ=117 and 590 ppm, respectively, were found by analysis of the rigid-lattice NMR line shapes of these molecules enclathrated in D2O hydrates. Spin-rotation interaction tensor components were obtained from the shielding constants and used to derive angular momentum correlation times for these molecules in the liquid from the spin-rotation contribution to the 19F relaxation rates. For CCl3F and ClO3F the available data agree almost quantitatively with the predictions of McClung’s J diffusion model for the relation between angular momentum and orientational correlation times of symmetric top molecules.
Ultrasonic studies of nematic–isotropic phase transitions
Authors: Gudgin Eva F. , Kruus Peeter , Munro Peter N.
Published: February 2003

Detailed studies have been carried out of the temperature dependence of the ultrasonic absorption in the isotropic–nematic phase transition range for p-methoxybenzylidene p-n-butylaniline (MBBA), and mixtures of MBBA with benzene and chlorobenzene. Although there is visual hysteresis in the MBBA systems, the ultrasonic absorption does not depend on whether the systems are cooled or heated. The volume averaged absorption for the MBBA–benzene system in the region of phase separation has a temperature dependence similar to that for MBBA–chlorobenzene, where the phases remain in suspension.
Critical test of equation-of-motion–Green’s function methods. II. Comparison with configuration interaction results
Authors: Herman Michael F. , Freed K. F. , Yeager Danny L. , Liu Bowen
Published: February 2003

A detailed comparison is presented between calculated equation-of-motion (EOM) ionization potentials and electron affinities and highly converged configuration interaction (Cl) results for a variety of atomic and molecular systems. Since an exact EOM calculation and a full Cl calculation within the same orbital basis set must yield identical results, this type of study allows for the separation of errors due to the approximations employed in solving the EOM equations from those errors arising from the use of an incomplete orbital basis set. The convergence of the EOM calculations at different levels of approximation is also investigated for these same systems. Important EOM basis operators, involving ionization and excitation (shakeup operators) or ionization and de-excitation, are numerically identified by configuration selection routines and are diagonalized rather than treated perturbatively. Terms involving second order couplings (arising from ground state correlation) between these shakeup states are calculated, as are the lowest order contributions from ionization and double excitation and from ionization and double de-excitation operators. These terms, which are normally neglected in EOM calculations, are found to be significant in certain cases. The agreement between the most sophisticated EOM and CI results is excellent for the molecular systems studied. The results justify the need for retention of higher order couplings, addition of double shakeup operators, and the adoption of a nonperturbative approach as described in paper I. The agreement is not as good for the atomic systems and possible reasons for these discrepancies are discussed.
Compatibility restrictions in the theory of antiresonance line shapes
Authors: Druger S. D.
Published: February 2003

The quasicontinuum correlation parameters that occur in the theory of antiresonance line shapes and radiationless decay, by virtue of being defined in terms of averages over the same set of quasicontinuum states, are shown to be restricted by conditions of mutual compatibility. These restrictions are analyzed in geometrical terms and some of their consequences are examined. A new correlation parameter λ is introduced and shown to qualitatively measure in many ways the overall consequences of correlations among the quasicontinuum couplings for many sparsely spaced states. A method is given for parametrizing the line shape and radiationless decay theory so as to satisfy the compatibility restrictions implicitly, thereby facilitating the analysis of experimental data. The application of the compatibility relations to the analysis of some recently reported line shape studies for molecules and solids is then discussed, including recent work on the optical absorption spectrum of boron-doped silicon.
Self-consistent molecular orbital methods. XX. A basis set for correlated wave functions
Authors: Krishnan R. , Binkley J. S. , Seeger R. , Pople J. A.
Published: February 2003

A contracted Gaussian basis set (6-311G**) is developed by optimizing exponents and coefficients at the Mo/ller–Plesset (MP) second-order level for the ground states of first-row atoms. This has a triple split in the valence s and p shells together with a single set of uncontracted polarization functions on each atom. The basis is tested by computing structures and energies for some simple molecules at various levels of MP theory and comparing with experiment.
A Mössbauer temperature study of two cold smectic (B and H) liquid crystals
Authors: LaPrice Walter J. , Uhrich David L.
Published: February 2003

We have used the Fe-57 Mössbauer effect (ME) to study solutions (0.2% by weight) of 1,1′-diacetylferrocene (DAF) in two liquid crystalline materials, 4-n-butoxybenzylidene-4′-n-′octylaniline (BBOA or 40,8) and 4-n-hexoxybenzylidene-4′-n-′ propylaniline (HBPA or 60,3). The ME parameters were determined for the temperature range 100–300 K in the crystalline solid phase of both systems and in the cold smectic B phase of BBOA and the cold smectic H phase of HBPA. Here ’’cold’’ means the smectic glass and the supercooled smectic phase. The lnf (recoil-free intensity) versus T plots exhibited linear Debye behavior for the solid phases of each system over the entire temperature range. The low temperature portion of the cold smectic lnf versus T data also exhibited Debye behavior for both systems. In both instances the smectic glass gave lower Mössbauer–Debye temperatures (ϑL) than the corresponding crystalline phase. For the smectic H glass of HBPA, ϑL=46 K and is independent of molecular orientation. For the smectic B glass of BBOA, ϑL=64 K for preferred molecular alignment parallel to the ME gamma direction and ϑL=49 K for perpendicular alignment. The smectic glass–supercooled smectic transition was determined to be Tg=175 K for BBOA and Tg=190 K for HBPA from the deviation of the lnf versus T data from linear behavior. Above Tg, the deviation from linear Debye behavior followed a (T−Tg)2 dependence. For DAF in HBPA, the intermolecular contribution to the Fe-57 vibrational ellipsoid (εL) was isotropic. For DAF in BBOA, εL declined linearly with increasing temperature below Tg. For 220–245 K line broadening and quadrupole relaxation were observed for the supercooled smectic H solution of HBPA. These results are accounted for using a model for rotational diffusion of the DAF molecule. The rotational diffusion apparently occurs without simultaneous translational diffusion.
Charge transfer in atomic collisions: The pair polarizability anisotropy
Authors: Hilton Peter R. , Oxtoby David W.
Published: February 2003

We present a simple illustrative one-electron scheme for the calculation of polarizability anisotropies of systems involving charge transfer processes. The method relies upon a frozen core assumption and the use of atomic Hartree–Fock wave functions to deduce the form of the one-electron potential by means of an inversion scheme. A basis set expansion technique is then applied to this potential. Polarizability anisotropies have been calculated for LiCl and KCl for internuclear separations up to 13 a.u. The agreement with Hartree–Fock finite-field calculations (which is generally good) reveals the dominance of charge transfer effects in these cases.
Comment on ‘‘Electron affinities from endothermic negative-ion charge-transfer reactions. IV. SF6, selected fluorocarbons and other polyatomic molecules’’
Authors: Lifshitz C. , Tiernan T. O. , Hughes B. M.
Published: February 2003

The energy thresholds for the dissociative electron transfer processes X−+SF6=SF5+F+X where X=O,S,F, brand I are discussed and electron affinities of SF5 radicals are obtained. (AIP)
Nonbonding intermolecular forces: The tetrathiafulvalene (TTF) dimer
Authors: Silverman B. D.
Published: February 2003

It is shown that the simplified version of local density functional theory proposed by Gordon and Kim can be used to accurately determine the location of interaction energy minima associated with large π orbital planar molecules interacting at van der Waals distances. The results of this calculation have contributed to the understanding of the origin of tetrathiafulvalene (TTF) stacking in neutral crystalline TTF and in the quasi-one-dimensional organic conductor, tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ). This technique should be generally useful in determining the origin of the stacking geometries of large planar molecules such as, for example, observed between nucleic acid constituents.
Nonradiative electronic relaxation of gas phase aromatic carbonyl compounds: Benzaldehyde
Authors: Hirata Y. , Lim E. C.
Published: February 2003

Radiationless transitions of gas phase benzaldehyde have been investigated, by studying the excitation energy and isotope dependence of its phosphorescence. As in aromatic hydrocarbons, S1→T1 intersystem crossing (ISC) dominates over S1→S0 internal conversion (IC) for low to moderate excess energies (i.e., for excitation energies corresponding to S0→S1 and S0→S2 absorptions), but S1→S0 IC becomes important for large excess vibrational energies. The excitation energy dependence of phosphorescence in the region of S0→S1 and S0→S2 absorptions therefore reflects the excess vibrational energy (in T1) dependence of T1→S0 ISC. This dependence is exponential, indicating that efficient intramolecular vibrational energy redistribution precedes T1→S0 ISC. It is shown that the rates of T1→S0 ISC and S1→S0 IC are dramatically reduced by deuteration of ring hydrogens, but only moderately affected by deuteration of the aldehyde hydrogen. The isotope effects on T1→S0 ISC are discussed in light of recent spectroscopic findings of Goodman and co-workers.
Quantum mechanics of the ground state of four identical fermions
Authors: Bruch L. W.
Published: February 2003

Wave functions for four identical spin-one-half fermions with total spin 0, 1, and 2 are constructed. Lower bounds on the ground state energies of these spin states are derived. The results are illustrated with an analysis of 4-fermions interacting via Hooke’s law potentials in three spatial dimensions. Other bounds on the ground state energy of four identical particles are also discussed.
Vibration→vibration energy transfer in methane
Authors: Hess Peter , Kung A. H. , Moore C. Bradley
Published: February 2003

Vibrational energy levels of methane in the range 2800 to 6000 cm−1 were excited by a pulsed tunable laser. Infrared fluorescence decays were observed at 294 K and analyzed to yield V→V energy transfer pathways and rates. Symmetric stretching excitation is converted to asymmetric stretching in the same molecule with a rate constant k1=(3.6±0.9) ×10−11 cm3 molecule−1 s−1 (P=0.09). The ν2 and ν4 bending vibrations are interconverted somewhat less rapidly. Stretching excitation is converted to bending with a rate constant of (0.8±0.2)×10−11 cm3 molecule−1 s−1 (P=0.022) for the stretching fundamentals and about twice that for overtone or combination levels. The rate of almost exactly resonant transfer of a vibrational quantum from one molecule to another was about (1.8±0.6)×10−11 cm3 molecule−1 s−1 (P=0.05) for transfer of a bending quantum from CH4(2ν4) and about three times less for transfer of a stretching quantum.
The Hellmann–Feynman theorem for approximate wave functions and its application to nonadiabatic coupling matrix elements with the aid of a coupled Hartree–Fock method
Authors: Habitz Peter , Votava Christian
Published: February 2003

Nonadiabatic coupling matrix elements are calculated by means of the Hellmann–Feynman theorem. Thereby the basis set dependence is investigated thoroughly for GTO basis sets. For every occupied AO, at least two polarization functions have to be included, of which the K shell p function have to be taken into special consideration. In this report we will show applications for the calculation of molecular forces on Hartree–Fock level. With a coupled Hartree–Fock method the gradient of orbital energies and nonadiabatic coupling matrix elements between different orbitals will be given. Our computations will deal with the molecules H2, N2, Li2+, and NeO.
The transport properties of binary gas mixtures in applied magnetic fields
Authors: Thomas James A. , Curtiss C. F.
Published: February 2003

Employing methods introduced by L. W. Hunter, scalar equations are obtained for the transport properties of binary gaseous mixtures in applied magnetic fields. The collision integrals occurring in these equations are generalizations of those discussed by L. W. Hunter and R. F. Snider. The shear viscosity of an atom–diatom mixture in an applied magnetic field is treated in detail. The basis set is truncated and the limit in which the concentration of the diatomic species is low is considered. The expressions obtained for the shear viscosity tensor are shown to be of the same form as earlier theoretical expressions.
Contracted Gaussian basis sets for molecular calculations. I. Second row atoms, Z=11–18
Authors: McLean A. D. , Chandler G. S.
Published: February 2003

Contracted Gaussian basis sets for molecular calculations are derived from uncontracted (12,8) and (12,9) sets for the neutral second row atoms, Z=11–18, and for the negative ions P−, S−, and Cl−. Calculations on Na...2p63p, 2P and Mg...2p63s3p, 3P are used to derive contracted Gaussian functions to describe the 3p orbital in these atoms, necessary in molecular applications. The derived basis sets range from minimal, through double-zeta, to the largest set which has a triple-zeta basis for the 3p orbital, double-zeta for the remaining. Where necessary to avoid unacceptable energy losses in atomic wave functions expanded in the contracted Gaussians, a given uncontracted Gaussian function is used in two contracted functions. These tabulations provide a hierarchy of basis sets to be used in designing a convergent sequence of molecular computations, and to establish the reliability of the molecular properties under study.
Vibrational energy transfers from the v=1 level of HBr to the v=1 level of CO, NO, N2, and O2, and to the 00° 1 level of CO2 and N2O
Authors: Seoudi B. , Doyennette L. , Margottin-Maclou M. , Henry L.
Published: February 2003

Rate constants for the vibrational energy transfer in HBr–M systems, with M=CO2, N2, N2O, CO, NO, O2, have been measured from 300 to 700 K using the laser-induced fluorescence technique. The results are compared to the values calculated from Shin’s model and from Dillon–Stephenson method using, respectively, a Morse potential and a dipole–dipole potential. From the analysis of our results on the HBr–M systems and of the results obtained by other authors on many HX–M systems (X being an halogen atom) a discussion is given about the respective role played by the attractive multipolar forces and by the repulsive forces in the V–V transfers.
Structure and dynamics of associated molecular systems. III. Computer simulation of liquid hydrogen chloride
Authors: McDonald Ian R. , O’Shea Séamus F. , Bounds David G. , Klein Michael L.
Published: February 2003

Several models for the interaction between hydrogen chloride molecules have been used in molecular dynamics simulations of the liquid. The models give rise to liquids in which molecules pack in very different fashions. In the absence of any experimental data on the liquid structure, it is difficult to argue strongly in favor of any particular model. However, the results on the liquid, when combined with solid state data, seem to favor those models which incorporate a weak but well-defined hydrogen bond.
On the many-body contributions to the 0K binding energy of solid argon
Authors: Aziz Ronald A.
Published: February 2003

The many-body contributions to the OK binding energy of solid Argon are discussed in terms of Aziz-Chen 13 potential.(AIP)
A more compact form of the equation of state for mixtures of hard spheres
Authors: Ponce-Ramirez L.
Published: February 2003

The hard-sphere model is used to predict a compact form of equation of state fluid mixtures.(AIP)
Theoretical prediction of the potential curves for the lowest-lying states of the isovalent diatomics CN+, Si2, SiC, CP+, and SiN+ using the a
b i
n
i
t
i
o MRD-CI method
Authors: Bruna Pablo J. , Peyerimhoff Sigrid D. , Buenker Robert J.
Published: February 2003

Large-scale CI calculations are reported for the potential curves of the isovalent series of diatomic systems CN+, Si2, SiC, CP+, and SiN+ in their lowest electronic states. The standard AO basis sets employed are of double zeta plus polarization quality and the CI method used is of the multireference double-excitation (MRD-CI) variety including individualized configuration selection and energy extrapolation. By including up to 17 reference species to generate the MRD-CI spaces (of orders up to 150 000) and by supplementing the AO basis with f functions it is found that the ground state of CN+ is the π4 1Σ+ species (as in isovalent C2) falling 0.1 eV below the σπ3 3Π state. This result is in significant disagreement with earlier theoretical predictions on this point, which have generally tended to place the 3Π state at least 0.3 eV below 1Σ+. The importance of using more than a single reference configuration in the CI calculations is underscored in this example. For Si2 a similar nearly isoenergetic relationship is noted for its lowest two electronic states, but in this case the competing states are 3Πu and 3Σg−, with 1Σg+ found to lie 0.7 eV higher in this spectrum. The mixed first- and second-row systems SiC and CP+ both show a clear 3Π ground state, well separated from both 1Σ+ and 3Σ−, but in SiN+ the absolute energy minimum is found to occur for 3Σ−, whereby the wide variations in the relative stabilities of all these states from one system to another is seen to be a consequence of the weakening of π bonding relative to σ as second-row atomic character is introduced into these molecules. Finally generally good agreement is observed between calculation and experiment in this study, with errors of 0.02 bohr and 70 cm−1 being indicated for known bond lengths and stretching frequencies.
Calculation of molecular polarizabilities using an anisotropic atom point dipole interaction model which includes the effect of electron repulsion
Authors: Birge Robert R.
Published: February 2003

The point dipole interaction model for molecular polarizability recently proposed by Applequist, Carl, and Fung is modified by replacing isotropic atomic point dipoles with anisotropic atomic point dipoles. The modified formalism, which is invariant to coordinate transformations, requires an additional empirical parameter for each atom type (ξA, the atomic anisotropy constant) and a single, global parameter applicable to all nonconjugated systems (κ, the repulsion exponent). The atomic polarizability tensor in the molecular environment is evaluated as a function of interatomic electron repulsion. This latter quantity is shown to be related to the degree to which bonding diminishes the polarizability of an atomic center in the direction (s) of the covalent bond (s). The anisotropic atom point dipole interaction model generates identical mean molecular polarizabilities as in the isotropic procedures of Applequist et al., while reducing the average error in the calculated molecular polarizability components to ∼7%. This error is comparable to experimental uncertainty.
Absorption spectra of heavily Cu+-doped KCl, SrCl2 and KI crystals
Authors: Tsuboi Taiju
Published: February 2003

Optical absorption and magnetic circular dichroism spectra have been investigated in heavily Cu+-doped KCl, SrCl2, and KI crystals (the concentration is more than 0.1 mole%). In KCl, CuCl microcrystal is formed in the annealed crystals and gives rise to two sharp bands in the 350–380 nm region, which are attributable to the Z1,2 and Z3 exciton bands in the microcrystal by analogy with the Z1,2 and Z3 exciton bands of pure CuCl crystal. The two bands of the microcrystal shift toward lower energy and approach to the pure CuCl exciton band spectrum with increasing microcrystal size. Similar microcrystal has been suggested to be formed in CuCl-doped SrCl2, and CuI microcrystal in CuI-doped KI.
On the vibrational structure in the luminescence spectra of uranium-activated sodium fluoride crystals
Authors: Bleijenberg K. C. , Breddels P. A.
Published: February 2003

In this paper we report on the luminescence properties of three selectively excited uranate centers in sodium fluoride crystals, viz. the (UO6⋅VF)×, (UO6⋅VF)×p and (UO5F)× centers. The emission transition is assigned to a 4γ7u→12γ8u transition. The emission spectra and the lowest energy band in the excitation spectrum show vibronic patterns associated with two electronic origins due to splitting of the excited electronic states under C4v symmetry. The relative intensities of the two vibronic patterns are temperature dependent. The temperature dependence of the decay time of the luminescence of the three uranate centers provides information about the transitions involved in the luminescence processes. An analysis of the vibrational structure in the luminescence spectra is presented.
Vibrational product state distributions of ion–molecule reactions by infrared chemiluminescence: Cl−+HBr,HI→HCl(v)+Br−,I−
Authors: Zwier Timothy S. , Bierbaum Veronica M. , Ellison G. Barney , Leone Stephen R.
Published: February 2003

Initial vibrational product distributions have been obtained for the thermal proton abstraction reactions, Cl−+HBr→HCl(v=0,1)+Br− and Cl−+HI→HCl(v=0,1,2)+I−. The experimental method utilizes detection of infrared chemiluminescence from the products of the ion–molecule reactions in a flowing afterglow. A detailed description of the apparatus design and characteristics is given. The initial relative HCl product vibrational distribution for the reaction Cl−+HI was determined to be Nv=1=1.0, Nv=2=0.85±0.05. The ratio of the total emission from Cl−+HBr to that from Cl−+HI was measured to be 39±2%. The results suggest substantial disposal of energy into product vibrations in these ion–molecule reactions.