bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Hartree–Fock–Slater calculations on diatomic molecules: Addendum
Authors: Becke A. D.
Published: February 2003

A completely numerical method for the computation of Hartree–Fock–Slater wave functions in diatomic systems has been previously reported and applied to the calculation of dissociation energies for selected first-row molecules. The previous results were obtained using spin-restricted orbitals. In this note, the results of new, fully spin-unrestricted calculations are presented.
Reply to ‘‘Comment on ‘Light scattering study of the phase transition in sym-triazine’ ’’
Authors: Yoshihara A. , Bernstein E. R. , Raich J. C.
Published: February 2003

Rae’s1 comments on the author’s paper concerning the phase transition in sym-triazine2 are answered. (AIP)
The electronic structure of polyphenyls and poly(p-phenylene)
Authors: Ford W. K. , Duke C. B. , Paton A.
Published: February 2003

The ultraviolet photoemission, optical absorption, and core-level shakeup spectra of p-phenylene oligomers and poly(p-phenylene) are analyzed using the spectroscopically parametrized CNDO/S3 model. The densities of valence states are calculated for these molecules and shown to provide a good description of available photoemission spectra. Photogenerated radical cation states can be delocalized over four or more phenyl moieties in the solid-state oligomers. The relationship between the density of valence states and the energy band structure of macromolecules of poly(p-phenylene) is established. The energies of the lowest energy electronic excitations of p-phenylene oligomers are evaluated and shown to describe well the available UV absorption and XPS shakeup measurements. The influence of disorder in the solid state is assessed by analysis of the influence of macromolecular conformation on the electronic structure.
Estimation of some matrix elements of the dynamical dipolar polarizability of iodine atom from long-range dispersion energy terms for molecular iodine
Authors: Vigue J. , Saute M. , Aubert-Frécon M.
Published: February 2003

The reduced matrix elements of the dynamical dipolar polarizability ε(k,k′) of the iodine atom are derived from the dispersion energy matrix for I2. The preponderance of the ε(0,0) term, proportional to the mean value C6 of the corresponding coefficients of all the different molecular states of I2, is strongly related to the quasi-isotropic feature of the C6 coefficient. Our value for the static dipole polarizability α is coherent with other determinations.
On the monotonicity of the atomic electron momentum density and shell structure of the radial momentum density
Authors: Gadre Shridhar R. , Chakravorty Subhas , Pathak Rajeev K.
Published: February 2003

Numerical investigations on the monotonicity of the electron momentum densities for atoms helium through xenon, using single-zeta and near Hartree–Fock wave functions, have been carried out. It has been noted that, in general, atoms with their ultimate p shells doubly occupied or more tend to show a nonmonotonic electron momentum density. An exception to this is the monotonic behavior exhibited by the elements helium through neon employing single-zeta wave functions. A study of the shell structure in momentum space for the above atoms reveals that all these atoms display, at the most, three maxima in their radial momentum density.
CASSCF/CI calculations for first row transition metal hydrides: The TiH (4Φ), VH (5Δ), CrH (6Σ+), MnH (7Σ+), FeH (4,6Δ), and NiH (2Δ) states
Authors: Walch Stephen P. , Bauschlicher Charles W.
Published: February 2003

By consideration of atomic coupling arguments and interaction of 4s23dn and 4s13dn+1 derived terms, the ground states of the transition metal hydrides are predicted to be TiH (4Φ), VH (5Δ), CrH (6Σ+), MnH (7Σ+), FeH (4Δ), CoH (3Φ), and NiH (2Δ). All of these systems have been studied by a CASSCF/CI(SD) procedure with the exception of CoH. The calculated parameters derived from the CASSCF/CI(SD) potential curves are in good agreement with the experimental values where known (no information exists for TiH and VH). Inclusion of atomic correlation leads to significantly better agreement with experiment particularly for Re. These improvements are related to a more balanced description of the atomic states in the correlated wave functions.
On the basis set superposition error in potential surface investigations. I. Hydrogen-bonded complexes with standard basis set functions
Authors: Leclercq J. M. , Allavena M. , Bouteiller Y.
Published: February 2003

The basis set superposition errors on the energy of the complexes FH ⋅⋅⋅ OH2 and FH ⋅⋅⋅ NCH are investigated at the SCF level. The two-dimension energy-potential surfaces, corresponding to the slow and fast frequencies of the hydrogen bridge, are calculated without and with the counterpoise correction. The corresponding quadratic, cubic, and quartic force constants are computed. Similar calculations are reported for the electric dipole moment and its derivatives. These investigations show that the basis set superposition error: (i) does not decrease, in the vicinity of the equilibrium configuration of the complex, when standard high-quality basis sets are used; (ii) shifts the minimum of the potential surface, distorts this surface, and changes the force constants in a significant but not drastic manner.
Fluids of hard diatomic molecules. I
Authors: Wertheim M. S.
Published: February 2003

The problem addressed is that of finding the complete orientation-dependent pair distribution function of a fluid of hard diatomic molecules. The treatment decomposes the Mayer f function into several terms and uses a graph-theoretical treatment. The basic idea is the explicit use of molecular geometry in constructing approximations. The fugacity expansion is found to be superior to the density expansion for this purpose. The neglect of large classes of graphs is shown to be exact for extremely asymmetric diatomics and is introduced as a new approximation for the less asymmetric case. Topological reduction of the reduced expansion leads to a result that resembles the density expansion, but contains an additional parameter. An integral equation of Ornstein–Zernike type is derived, and an approximation for closing the equation is suggested. The resulting equations are calculationally tractable and can be used to obtain both the centers correlation function and the higher harmonics of the pair distribution function. The relation to RAM perturbation theory is discussed briefly.
Charge carrier escape rate from electrode–liquid interface
Authors: Prock Alfred , Das Kamalendra N. , Melman Paul
Published: February 2003

Carrier photoinjection after excitation of low dielectric constant medium has been described in terms of forced diffusion of ions away from image forces at the electrode. The rate of this detachment process is expected to have a characteristic dependence on the strength of applied electric field at the electrode. We describe an extrinsic photoconductivity experiment using a thin layer cell where space charge modification by dark current of the local field due to injection or blocking effects can be made negligible. At high applied fields we find quantitative agreement of photocharge yield with the predicted characteristic behavior. This agreement strongly supports the correctness of the ion detachment model in such systems.
Convergence and memory effects in stochastic treatment of collisional energy transfer
Authors: Makowski A. J. , Lin C. S.
Published: February 2003

Second and fourth order Markovian (M) and non-Markovian (NM) equations were solved analytically for stochastic treatment of collinear collision between two identical diatomic molecules. It is shown that when v/2ωL≪1 is satisfied the Markovian approximation (omission of memory) is sufficiently valid and all four approximation methods (2M, 4M, 2NM, 4NM) show good agreement with exact semiclassical theory. Convergence of the transition probabilities vs perturbation expansion of potential is slow and nonmonotonic. However, case by case, non-Markovian approximation gives a faster convergence than the Markovian.
Anomalous temperature-dependent phosphorescence of Cu porphin in anthracenea)
Authors: Bohandy J. , Kim B. F.
Published: February 2003

The temperature dependence of the phosphorescence spectrum of copper porphin in anthracene has been studied from room temperature down to 8 K and the 4.2 K spectrum has been obtained. A 23.4 cm−1 crystal field splitting of the orbital components of the TQ state was observed. The 0–0 transition appears abruptly at approximately 25 K and increases rapidly in intensity as the temperature is lowered. A model involving energy transfer from the copper porphin to the triplet exciton band of anthracene gives a satisfactory explanation for the anomalous temperature dependence of the copper porphin phosphorescence intensity.
Rayleigh–Brillouin scattering of transverse and longitudinal acoustic waves in a supercooled viscoelastic liquid
Authors: Wang C. H. , Liu Quan-L.
Published: February 2003

Rayleigh–Brillouin spectra of 3-phenyl propanol are studied over the temperature range from −119.5° to 98.1 °C. The orientation relaxation time is obtained as a function of temperature. The depolarized spectra exhibit clear shear wave sidebands at temperatures below −29.5 °C. The polarized spectra give peaks due to the longitudinal acoustic wave whose frequency displays kinks at the glass transition temperature and at 37 °C (Tk). Tk is 55 °C above the melting temperature (−18 °C). The shear wave frequency decreases linearly with increasing temperature. The experimental results on the VH scattering spectra are analyzed according to viscoelastic theories based upon the Voigt and Maxwell models. Comparison of the theory with observed spectra shows that the Voigt model gives a better fit to the experimental data. Microscopic theory has also been developed to derive the Voigt and Maxwell models. Angular dependent studies are proposed to differentiate the various theories which give different predictions about the physical nature of the parameters.
State resolved rotational excitation in HD+D2 collisions. II. Angular dependence of 0→2 transitions
Authors: Buck U. , Huisken F. , Maneke G. , Schaefer J.
Published: February 2003

Time-of-flight spectra for the scattering of HD molecules from D2 molecules have been measured at a collision energy of E=70.3 meV over a range of center-of-mass scattering angles from 45° to 158°. The spectra reveal clearly resolved transitions at the energy loss ΔE=33 meV which corresponds to 0→2 transitions of HD and the double transition 0→1 of HD and 0→2 of D2. The differential cross sections derived from these spectra increase with increasing scattering angle from 1.7% to 34.7% of the elastic cross section. The pure 0→2 transition of D2 which only needs 22 meV to be induced could not be detected within our experimental sensitivity of 0.02 Å2/sr. Closed coupled calculations based on the ab initio potential surface of Meyer and Schaefer show that this result can be explained by the different coupling terms which are responsible for these transitions. In contrast to the 0→1 transition the 0→2 transition of HD proved to be sensitive to the anisotropic part of the interaction potential for the homonuclear system. The comparison of experimental and calculated cross sections for the ab initio potential of Meyer and Schaefer reveals discrepancies for the 0→1 transition of HD, but shows agreement for the 0→2 transition of HD at intermediate angles.
State resolved rotational excitation in D2+H2 collisions
Authors: Buck U. , Huisken F. , Kohlhase A. , Otten D. , Schaefer J.
Published: February 2003

In a crossed molecular beam experiment time-of-flight distributions of ortho D2 molecules scattered from normal H2 (nH2) and para H2 (pH2) have been measured in a center-of-mass angular range of 75° to 180°. The collision energies were 84.1 and 87.2 meV, respectively. In all spectra the rotational excitation of D2 from j=0 to j=2 has been resolved. With pH2 as secondary beam the same transition could also be observed for H2. The measurements show that the probability for rotational excitation of D2 depends on whether the scattering partner H2 is rotating (nH2) or not (pH2). In the first case the cross sections are larger by a factor of approximately 2. The reason for this behavior is the presence of an additional interaction term which is at long range distances, identical to the quadrupole–quadrupole interaction and which is absent if H2 is in the j=0 state. The experimentally derived differential cross sections for the rotational excitation of D2 and H2 are compared with theoretical results obtained by close coupling calculations based on the ab initio potential surface of Meyer and Schaefer. The comparison shows a remarkable agreement. However, small deviations in the positions of the diffraction oscillations of the elastic differential cross section curve suggest that the isotropic potential term has to be shifted to smaller distances. In order to maintain the relative position of the inelastic differential cross section curves which are well predicted by the ab initio potential the same shift has to be applied to the anisotropic potential terms.
Calculation of higher-order semiclassical scattering phase shifts: The effect of a barrier maximum
Authors: Luppi Jussi , Pajunen Petri
Published: February 2003

Evaluation of high-order semiclassical scattering phase shifts is extended to situations involving a potential barrier. Calculations by using appropriate semiclassical phase shift formulas yield accurate results for energies above and below as well as in the immediate neighborhood of the barrier maximum.
The dissociation energies of the diatomic alkali hydrides
Authors: Yang S. C. , Nelson D. D. , Stwalley William C.
Published: February 2003

A new method for estimating the dissociation energies for the alkali hydride molecules is reported. It involves extrapolating the known Rydberg–Klein–Rees potential curve of the A 1Σ+ state to the ionic–covalent avoided crossing point. The estimate dissociation energies De(X) are 16 000±400 cm−1 for NaH, 15 020±400 cm−1 for KH, and 14 580±600 cm−1 for RbH.
Intermolecular attractive forces in triplet excimers: L-shaped excimer of naphthalene
Authors: Lim B. T. , Lim E. C.
Published: February 2003

Experimental evidence is presented which indicates that the triplet excimer of naphthalene is L shaped. The preference for an L-shaped structure is interpreted as a compromise between the dispersion force which favors a coplanar structure and the electrostatic force which favors a P-shaped structure. The intermolecular attractive forces which are responsible for the formation of triplet excimers (of aromatic hydrocarbons) are therefore similar to those responsible for the formation of the ground state van der Waals dimers.
On the localization of the resonance state wave function in the complex coordinate method
Authors: Deguchi K. , Kato Y. , Nishikawa K. , Aono S.
Published: February 2003

The localization of the resonance state wave functions is investigated in the complex coordinate method within the framework of a simple two-state model. (AIP)
Dynamics of fluorescence quenching in micellar systems
Authors: Infelta Pierre P. , Grätzel Michael
Published: February 2003

Tachiya’s criticism of the authors’ previous publication regarding a kinetic model to explain fluorescence quenching in organized assemblies, such as surfactant micelles is answered. (AIP)
Raman scattering study of pressure effects on the structure and the coordination-induced charge redistribution in 4-cyanopyridine
Authors: Wong P. T. T.
Published: February 2003

The Raman spectra in the frequency regions of the lattice and the internal modes of the crystalline CNPy and Zn(CNPy)2Cl2 have been measured at various pressures up to 16.5 and 20 kbar, respectively. A structural phase transition at 10 kbar in CNPy and two at 8.2 and 18 kbar in Zn(CNPy)2Cl2 were observed. At high pressure, CNPy suffers a lattice distortion along the eigenvector of a soft phonon, and Zn(CNPy)2Cl2 undergoes a molecular configuration distortion which leads to the softening of a rotational phonon. The charge distribution on the CNPy molecule is changed by coordination and also by external pressure and this charge redistribution has been correlated with the vibrational spectral changes.
Explicit construction and algebraic structures of Hückel propagators and their applications
Authors: Nishikawa K. , Yamamoto M. , Aono S.
Published: February 2003

Propagator theory is developed in the Hückel model. Analytical expressions of Hückel propagators for linear and ring molecules with and without bond alternation are obtained by analyzing the Dyson’s equation. Further, the propagators for molecules of complex topological structures are constructed in systematic ways with those for simpler linear and ring systems. By applying the partitioning technique to the Dyson’s equation, it is easily shown that the propagators of complex systems are formally brought into the same form as those for the simple ones with renormalized Coulomb and resonance integrals. Finally, some physical quantities are directly evaluated by the integration method proposed by Coulson.
A study of the liquid–vapor interface of mercury: Computer simulation results
Authors: D’Evelyn Mark P. , Rice Stuart A.
Published: February 2003

This paper extends our recently proposed pseudoatom theory for the liquid–vapor interface of simple metals to mercury. An important difference between mercury and the alkali metals is that in the former the metal–nonmetal transition takes place over a range of density positioned at much higher density than the critical density. A modified pseudoatom model, with an improved treatment of the metal–nonmetal transition, is presented. Using the modified effective Hamiltonian for the ions, Monte Carlo simulations of the liquid mercury surface have been carried out. The simulations reveal a highly structured liquid–vapor transition zone, with large amplitude density oscillations. The metal–nonmetal transition is found to play a critical role in determining the liquid–vapor interface structure, and it gives rise to a partial monolayer of nonmetallic atoms adsorbed on the metal surface. A detailed comparison of our results with the existing experimental and theoretical work, particularly the x-ray reflectance data of Lu and Rice, is presented.
1H NMR study of the phase separation and the behavior of hydrogen in Ti1−yVyHx
Authors: Hayashi Shigenobu , Hayamizu Kikuko , Yamamoto Osamu
Published: February 2003

The behavior of hydrogen in the Ti–V hydrides was studied by 1H NMR spectroscopy. FT spectra and spin-lattice relaxation times of Ti0.60V0.40H0.90, Ti0.40V0.60H0.79, and Ti0.20V0.80H0.77 were measured in a temperature range between 125 and 425 K. A phase separation occurs in the Ti–V hydrides by hydriding, and the β–Ti–V–H and the γ–Ti–H phases are dominant. The former phase increases with temperature, accompanied by the decrease in the latter. The composition in the γ–Ti–H phase is almost independent of temperature, while it changes with temperature in the β–Ti–V–H phase. In the β–Ti–V–H phase, hydrogen-ordered structures are assumed to be formed, and the hydrogen diffuses faster than in β–VHx and γ–TiHx.
Thermal diffusivity in mesophases: A systematic study in 4-4′-di-(n-alkoxy) azoxy benzenes
Authors: Urbach W. , Hervet H. , Rondelez F.
Published: February 2003

We present a systematic study of thermal diffusivity in the nematic liquid crystalline phase of 4-4′-di-(n-alkoxy) azoxy benzenes and several other materials. The data allow to separate the respective contributions of the rigid central core and of the flexible aliphatic chains. For the component of the diffusivity tensor parallel to the long molecular axis, it is found that they differ by as much as a factor of 6 in favor of the core contribution. Combining the present observations with our earlier results, we are now able to draw general conclusions on the thermal diffusivity in a nematic and smetic A, B, and C phases. We have also developed two semiquantitative models based, one on a static network of distributed resistances, and the other on an extension of the Eyring kinetic model for the thermal conductivity of simple liquids. Only the dynamic model yields a satisfactory description of our data. The distance over which the thermal energy is not transferred instantaneously upon collision between two neighboring molecules is found to correspond to the aliphatic chain length (calculated for a freely rotating chain). Using this formalism, a priori calculations of the thermal diffusivities can be performed, to better than 20%, for any rodlike liquid crystalline material.
Quantum dynamical model of laser-stimulated isotope separation of adsorbed species: Role of anharmonicity, coupling strength, and energy feedback from the heated substrate
Authors: Lin Jui-teng , George Thomas F.
Published: February 2003

A quantum model of a heterogeneous system consisting of a mixture of isotopes adsorbed on a solid surface and subjected to laser radiation is presented. The model system is described by a total Hamiltonian including direct and indirect (surface-phonon-mediated) couplings. The equations of motion are derived in the Heisenberg–Markovian picture in which the many-body effects of the surface phonon modes and the adspecies are reduced to an overall broadening (damping factor) given by the sum of the energy (T1) and phase (T 2) relaxations. The effects of the dephasing and anharmonicity on the average excitation are investigated. The ‘‘bistability’’ feature with a red-shifted optimal detuning is discussed in terms of the solution of a cubic equation. A diagonalization procedure is presented in a new basis which reveals the effects of the coupling strength, the frequency difference, and the level width of the isotopes on the total steady-state excitation, which in turn reflects the surface spectrum of the model system. Finally, the isotope selectivity given by the numerical results of the time-integrated excitation is discussed. It is shown that the optimal detuning for a weak coupling strength is further red-shifted for a strong isotopic coupling strength. Finally, energy feedback effects of the bath modes on the excitations of the active modes are investigated by combining a quantum excitation equation and a classical heat diffusion equation.
The observation of one-phonon assisted selective desorption and adsorption of He atoms in defined vibrational levels on a LiF (001) single crystal surface
Authors: Lilienkamp G. , Toennies J. Peter
Published: February 2003

By choosing the appropriate incident angle it has been possible to inject the nearly monoenergetic (Δv/v≊1%) He atoms of an incident beam (18 meV) into one of the four bound states of the atom–LiF(001) surface potential. The final angular distributions of the atoms which have been inelastically scattered by phonons out of these bound states have been measured for the 〈100〉 and 〈110〉 directions of LiF (001). For the low-lying states these distributions are peaked at large final angles (≊75°) near grazing and are different from the distributions for the atoms directly inelastically scattered. The time of flight distributions indicated a predominance of annihilation events indicating that the atoms have been ejected by gaining the minimum amount of energy for release from the surface. The initial angle distribution of He atoms inelastically entering the 〈110〉 v=0 ground state could also be measured by monitoring the flux at a unique magic angle at which the atoms can leave this state by the reverse of selective adsorption. The time of flight spectra reveal that the atoms in this case were trapped by a creation process. The two processes of adsorption and desorption are related by microscopic reversibility. The results are discussed in terms of a simple quantum resonance theory.
An EPR study of the reaction between poly(p-phenylene sulfide) and electron-acceptor dopants
Authors: Kispert L. D. , Files L. A. , Frommer J. E. , Shacklette L. W. , Chance R. R.
Published: February 2003

EPR spectra for electron-acceptor doped poly(p-phenylene sulfide) are reported. The g values obtained from these spectra correspond to an electron density centered around a divalent sulfur radical cation R–S–R. This assignment is supported by corresponding EPR data from an oligomeric model compound φ–S–φ–S–φ (φ=phenyl). The g value of the sulfur-based radical cation of doped poly(p-phenylene sulfide) distinctly contrasts the nearly free electron g values obtained from EPR measurements on poly(p-phenylene) and its oligomer p-terphenyl.
Theoretical studies of H2–H2 collisions. IV. Ab initio calculations of anisotropic transport phenomena in para-hydrogen gasa)
Authors: Köhler Walter E. , Schaefer J.
Published: February 2003

The temperature dependence of the effective Waldmann–Snider cross sections determining the Senftleben–Beenakker effects of viscosity and heat conductivity has been studied for pH2 gas between 10 and 200 K. From ab initio nonspherical potentials of H2–H2, scattering matrices have been determined in close-coupling calculations. From these, the elements of the scattering amplitude matrix have been obtained and used as input quantities for the evaluation of the various Waldmann–Snider collision integrals. The results of these first ab initio numerical calculations of anisotropic transport coefficients show excellent agreement of calculated and measured effective cross sections, especially for the most recent improved version of the interaction potential. In addition, it has been shown that the polarization production cross sections are quite sensitive to the potential anisotropy.
Scattering off an ellipsoid: A semiclassical theory
Authors: Eu Byung Chan , Sink Michael L.
Published: February 2003

The WKB approximation is developed for scattering of an atom by an ellipsoidal particle and elastic scattering cross sections are calculated by using the WKB phase shifts in the prolate spheroidal coordinates and uniform WKB approximations for angular spheroidal wave functions. The calculation of cross sections requires the solution of an elliptic boundary condition and is quite simple compared to the calculation in the close coupling theory in the spherical coordinate representation. A version of close coupling theory is briefly discussed in the prolate spheroidal coordinates.
Arbitrary order functional sensitivity densities for reaction-diffusion systems
Authors: Dacol D. K. , Rabitz H.
Published: February 2003

The concept of functional sensitivity analysis in the study of diffusion processes in a chemically reacting environment is reviewed and extended to include the notion of arbitrary order functional sensitivity densities. A new perspective on its physical and mathematical basis is offered through a detailed discussion of the motivation behind the formal procedure adopted. The arbitrary order functional sensitivity densities (defined as arbitrary order functional derivatives of a chemical species concentration with respect to the space and time dependent parameters of the system) are shown to obey certain differential equations that can be solved with the help of a Green’s function. This Green’s function is the inverse of a differential operator that defines an associated linear system in the application of Lyapounov’s linearized stability theory to (in general nonlinear) reaction-diffusion systems. It is found that the Green’s function can be regarded as a concentration response function which allows for an interpretation of the sensitivity densities as generalized response functions. Finally, an illustration of the use of those techniques is provided by applying them to the case of a linear reaction-diffusion system.
Analysis of the 254.7 nm absorption system of carbonyl fluoride
Authors: Judge R. H. , Moule D. C.
Published: February 2003

The 230 nm absorption spectrum of carbonyl fluoride has been recorded in the vapor phase at 25° and −78 °C at path lengths up to 48 m. In all, 170 bands were observed in the spectrum and were assigned to vibrational activity in ν1′, ν2′, ν3′, ν4′, and ν5′. The presence of temperature sensitive bands attributed to ν4′′ leads to the interpretation that the excited state is nonplanar. Combination differences isolating ν4′′ show that the inversion doubling splitting is less than the experimental error for levels 4+ and 4− in the Q4 mode of vibrational excitation. A fit of the G4 term values to the energy levels derived from a quadratic-Lorentzian function yielded a central barrier of 8200 cm−1 and an out-of-plane angle of 31.8° for V(Q4). The high barrier is attributed to an inductive effect from the fluorine atoms brought about by a relaxation of the symmetry from C2v to Cs on electronic excitation.
Mössbauer spectroscopy on high-spin d5 iron complexes: Crystal field calculations
Authors: Spartalian K. , Carrano Carl J.
Published: February 2003

Mössbauer spectra of high-spin ferric Fe(EHPG) compounds in frozen solution have been recorded at 4.2 K in a small applied field. The spectra have been analyzed in terms of a spin Hamiltonian with S=5/2 used as an intermediate step for generating a crystal field model that has the ground sextet 6A1 and three excited quartet states appropriately spaced in energy. The model has been found to be appropriate for g=4.3 high-spin ferric complexes with spin Hamiltonian D values in the range 0.6–1.7 cm−1. It is shown that the model can provide a three-way correlation of the relevant data obtained by Mössbauer, EPR, and optical absorption spectroscopy.
Bond polar parameters from infrared intensities in X2CY molecules
Authors: Nikolova B. , Galabov B. , Lozanova C.
Published: February 2003

The integrated gas-phase infrared intensities in F2CO, Cl2CO, F2CS, and Cl2CS are interpreted in terms of bond polar parameters using recently proposed parametric model of IR intensities. The calculated values for the bond parameters correlate with the electronegativities of the atoms forming the chemical bonds in these molecules. It is concluded that the band intensities in the infrared spectra of these systems are largely dependent on the static charge distribution.
Diffusion in concentrated hard sphere dispersions: Effective two particle mobility tensors
Authors: Snook I. , van Megen W. , Tough R. J. A.
Published: February 2003

In view of the practical difficulties already encountered plus those anticipated in the implementation of many-body hydrodynamic interactions, we examine a number of empirically screened two particle mobility tensors. The empirical screening constant(s), which depend on the dispersion concentration, are adjusted to give the best agreement with available experimental mutual and local self-diffusion constants for concentrated hard sphere dispersions. These diffusion constants are obtained experimentally from the first cumulant of the coherent intermediate scattering function in the small and large wave vector limits. We find that the experimental data can only be satisfactorily reproduced by employing a pair mobility tensor containing two adjustable screening terms. The predictions of the final mobility tensor at intermediate wave vectors are also qualitatively consistent with experiments.
Response to ‘‘Comment on: ‘A quantum analog to the classical quasiperiodic motion’’’
Authors: Hose Gabriel , Taylor H. S.
Published: February 2003

The comments Mukamel2 on a previous paper by the authors1, regarding the quantum analog to quasiperiodic motion in classical mechanics are answered. The effective Hamiltonian is defined for each state and yields the quasiconstants of the motion for the state of interest. This is not the Heff given by Mukamel2. (AIP)
The dynamics of ethylene dimer infrared photodissociation in pulsed molecular beamsa)
Authors: Hoffbauer Mark A. , Liu Kopin , Giese Clayton F. , Gentry W. Ronald
Published: February 2003

Molecular beam experiments have been carried out on the infrared photodissociation of the (C2H4)2, (C2D4)2, and (C2H4)⋅ (C2D4) van der Waals molecules. Measurements of the frequency and fluence dependences of the photodissociation cross sections were performed over the CO2 laser frequency range from 900 to 1100 cm−1, which covers the region of the ν7 out-of-plane vibration of C2H4 and the ν12 in-plane vibration of C2D4. In addition, the monomer product speed and angle distributions were measured in order to obtain information on the final energy disposition in the products. Absorption in either vibrational mode induces dissociation of the cluster, but the linewidth associated with excitation of the ν7 mode of C2H4 is about four times larger than that associated with excitation of the ν12 mode of C2D4. Two-laser ‘‘hole-burning’’ experiments demonstrate the homogeneity of the ground-state populations. The absorption intensities are not simply proportional to the number of molecules in the cluster capable of absorbing at a given frequency but instead appear to contain information on the structure of the dimer. The dissociation products are scattered isotropically in the center of mass system, with average recoil velocities which correspond to only a small fraction of the available energy appearing in translation. In the case of (C2H4)2, the lack of vibrational modes at the corresponding product internal energies implies that the remaining energy goes into product rotation. Based on the rather detailed spectroscopic and dynamical information provided by these experiments, and the assumption of a skewed parallel structure for the dimer, qualitative arguments are presented that the observed linewidths are determined by the rates of the mode-specific anharmonic coupling of the monomer vibrations to the van der Waals coordinates, but not necessarily by the vibrational predissociation rates.
Triplet exciton lifetime under pressure in ‘‘pure anthracene’’
Authors: Arnold S. , Hassan N.
Published: February 2003

The triplet exciton lifetime in ‘‘pure’’ anthracene crystals is found to decrease by as much as a factor of 3 at room temperature under pressures up to 6.4 kbar and in a reversible fashion. Temperature measurement under pressure from 200 to 400 K show that the effect is due to a state ∼0.3 eV below the exciton band. Experiments with tetracene doped anthracene revealed that trapping by tetracene is increased by a factor of 2 over the same pressure range, indicative of enhanced diffusion. A comparison with the ‘‘pure’’ anthracene effect reveals that pressure enhanced diffusion is insufficient for explaining this effect; the cross section for capture by the 0.3 eV state must change by more than a factor of 4 in going from 1 atm to 6.4 kbar. A triplet excimer is invoked for explaining our results, consistent with earlier work. The pressure dependence of the mean capture cross section for this species is determined.
Electronic properties of alkali trimers
Authors: Martins José Luís , Car Roberto , Buttet Jean
Published: February 2003

The electronic properties of the alkali trimers Li3, Na3, and K3 are studied using the pseudopotential and the local-spin-density approximations. More than 100 configurations were calculated for each trimer in order to obtain a complete picture of the adiabatic Born–Oppenheimer surfaces. The equilibrium geometry of the trimers are Jahn–Teller distortions of an equilateral triangle. Although the three surfaces are quite similar, Li3 is more affected than Na3 or K3 by the dynamical character of the Jahn–Teller distortion. The calculated ionization potentials agree very well with the experimental values and the qualitative features of the Born–Oppenheimer surface are confirmed by recent ESR experiments.
Electron thermalization in gases
Authors: Shizgal B.
Published: February 2003

The energy relaxation of energetic electrons is determined with a moment method solution of the hard sphere Lorentz–Fokker–Planck equation. The convergence of the expansion of the electron speed distribution function in speed polynomials is rapid and the energy relaxation can be written explicitly as a sum of a small number of exponential terms characterized by the lowest eigenvalues of the Lorentz–Fokker–Planck equation. The decay of the directed velocity is examined with a discrete ordinate method. The rate of convergence vs the number of quadrature points is extremely rapid and for particular values of the initial electron energy, an exact result can be obtained.
Thermodynamic properties of a square-well fluid in the liquid and vapor regions
Authors: Carley David D.
Published: February 2003

The thermodynamic properties of a square-well fluid are computed for temperatures below the critical temperature using a perturbation technique. Thermodynamic functions such as pressure, internal energy, and the Helmholtz function are tabulated and compared with computer simulation results. The critical point is found and the liquid–vapor phase diagram is obtained. The perturbation method uses high temperature parametric integral equation results as an original reference system and applies first order perturbation theory to the Helmholtz function. The pair potential (φ) is written as the sum of two parts, a reference potential (φr) and a perturbing potential (φp) and the separation is established by the relationship φr=αφ where α is a constant. This separation leads up to a particularly simple method of computing thermodynamic properties when the pressure and internal energy are known along one isotherm. In the case of the square-well potential this approximation leads not only to simple equations but the results also appear to be reasonably accurate.
13C NMR chemical shift tensors of metal carbonyls
Authors: Gleeson James W. , Vaughan Robert W.
Published: February 2003

The principal components of the 13C NMR chemical shift tensors of metal carbonyls containing between one and six metal atoms were determined from their powder patterns. The tensors of terminally bound CO groups are highly anisotropic (380±60 ppm) and nearly axially symmetric. The tensors of bridging CO groups are much less anisotropic, due to significant asymmetry in the electron orbitals about the C–O internuclear axis. The tensors vary only slightly for different transition metals. There is no intramolecular rearrangement of the metal carbonyls in the solid state at frequencies greater than 10 kHz, except in Fe3(CO)12.
Photoelectron spectra of the lanthanide trihalides and their interpretation
Authors: Ruščić B. , Goodman G. L. , Berkowitz J.
Published: February 2003

The He i photoelectron spectra of gaseous LaCl3, LaBr3, LaI3, CeBr3, CeI3, NdBr3, NdI3, ErI3, LuBr3, and LuI3 have been obtained. They display a pronounced increase in splitting, and hence a progressively clearer definition of peaks in the valence band as either the halogen or the lanthanide increases in atomic number. These experimental features, together with a refined relativistic Xα DVM calculation using the von Barth–Hedin potential, have enabled us to assign these peaks with confidence. The He ii photoelectron spectra of CeBr3, NdBr3, and LuI3 are also presented. They reveal that the 4f-like ionizations of early lanthanide members (e.g., Ce) occur at lower energy than the ligand valence band, but that those of late members (e.g., Lu) are corelike. The aforementioned calculations reproduce this behavior quantitatively. They also help to rationalize a bimodal behavior in the valence band; the spectra with less than half-filled 4f shell are very similar, as are those with more than half-filled 4f shell, but the two groups are distinctly different. The width of the valence bands, which varies over a factor 2.5, is correctly reproduced. The calculations have been been extended to include fluorides, where contact is made with electron impact mass spectrometry and x-ray photelectron spectra of solids, thereby enabling corrections to be made to the latter. The fragmentation behavior in mass spectrometry is then related to the states observed in photoelectron spectroscopy. Both the calculations and these experimental comparisons yield a picture in which the lanthanide fluorides display predominantly ionic bonding (Ln2.2+); the bonding takes on succesively more covalent character as one proceeds to chlorides (Ln1.6+), bromides (Ln1.3+), and iodides (Ln1.0+).
Simulation of quadrupole disturbed NMR field spectra by using the exact solution of the Hamiltonian: Application to zinc
Authors: Abart J. , Palangié E. , Socher W. , Voitländer J.
Published: February 2003

The NMR signals of 67Zn in polycrystalline zinc metal have been observed at frequencies between 8.8 and 13 MHz. Because of the large quadrupole interaction, the spectra have been recorded by sweeping the magnetic field. In order to evaluate the spectra with high accuracy, we have developed a variational method which is based on the exact solution of the NMR-Hamiltonian, for calculating the transition fields, the appropriate transition intensities and from those field spectra. From the comparison between the simulated and the experimental spectra of Zn, we evaluated a quadrupole coupling constant e2qQ/h of 12.73 (4) MHz, an isotropic Knight shift Kiso of 0.15 (3)% and an axial one Kax&d of 0.03 (3)%. The results are discussed in comparison with already known data.
Resonance Rayleigh scattering of cyanine dyes in solution
Authors: Anglister J. , Steinberg I. Z.
Published: February 2003

Every process of light absorption is inherently associated with a resonance scattering of the incident beam regardless of the nature of the absorbing molecules. Both the real and imaginary parts of the refractive index contribute to the resonance scattering, and marked depolarization is expected to be observed as a rule in the light scattered by complex molecules. The resonance and near-resonance Rayleigh scattering has been measured for a number of cyanine dyes: pseudocyanine, orthochrome T, 1,1′-diethyl-2, 2′-pyridyl-quinolyl cyanine, and pinacyanol chloride, in a number of solvents. In no case was the measured scattering intensity weaker than that expected theoretically, and good agreement between theory and experiment was found as a rule at the blue part of the absorption bands. In contrast, the measured scattering intensities exceeded (by up to fourfold) the theoretically expected values at the red parts of the absorption bands. Possible reasons for this discrepancy are discussed.
The structure of metallic complexes of polyacetylene with alkali metals
Authors: Baughman R. H. , Murthy N. S. , Miller G. G.
Published: February 2003

The crystal structures of sodium, potassium, rubidium, and cesium doped polyacetylene have been determined using crystal packing and x-ray diffraction analyses. Each of these metallic complexes is tetragonal, with the polyacetylene chains forming a host lattice in which the alkali metal ions are present in channels. Lithium appears to be too small to stabilize the channel structure and an amorphous structure is observed. Predicted unit cell parameters and x-ray diffraction intensities are in agreement with observed values. Similarities with the alkali metal doped graphite suggest that hybridization between carbon pz orbitals and metal s orbitals occurs. Such hybridization is expected to result in a high conductivity component normal to the chain direction. On the other hand, direct overlap between polymer chains appears small, since alkali metal columns separate polymer chains. Compositions calculated for the channel structures (from meridional diffraction spacings, the intensity of equatorial diffraction lines, measured volume expansion, and distances in model complexes) all range from y=0.12 to 0.18 for (CHMy)x, where M is sodium, potassium, rubidium, or cesium.
SCF, IEPA, PNOCI, and CEPA2-PNO analysis of the anisotropy of (H2)2 interaction near the minimum in the van der Waals interaction
Authors: Burton Peter G. , Senff Ulrich E.
Published: February 2003

The nature of the anisotropy of the H2–H2 interaction is investigated in some detail. The electron correlation effects and their influence toward the anisotropy of the (H2) dimer interaction are discussed in some detail. (AIP)
Electric dipole moment and quadrupole hyperfine structure of OC–HCl and OC–DCl
Authors: Altman R. S. , Marshall M. D. , Klemperer W. , Krupnov Andrei
Published: February 2003

Microwave and radio frequency spectra of the weakly bound complex OC–HCl and two of its isotopes measured in static electric field are reported. The values of the dipole moments and the hyperfine constants determined are         This molecular complex is shown to have a significant induced dipole moment which is much larger than elementary electrostatic calculations predict. The ratio of the electric quadrupole coupling constant in the DCl complex to that of free DCl is shown to be the same using either the chlorine or the deuterium, indicating no measurable distortion in the electric field gradient at the deuterium nucleus.
Raman spectroscopy of molecular monolayers without giant field enhancements
Authors: Tsang J. C. , Avouris Ph. , Kirtley J. R.
Published: February 2003

Raman spectra have been obtained from molecular monolayers of nitrobenzoic acid and aminobenzoic acid on AlOx and in Ag and Sn tunnel junctions. The large electromagnetic field enhancement necessary for surface enhanced Raman scattering experiments from roughened noble metal surfaces is replaced by the enhanced sensitivity of a cooled, optical multichannel detector. The behavior of the Raman intensity for a molecule adsorbed on a nonresonant metallic substrate has been studied and compared with theory. The evolution of the vibrational spectrum of the adsorbate during the fabrication of an inelastic electron tunneling spectroscopy junction has been observed and the dominant spectral changes assigned to the initial adsorption of the molecule on the oxide surface.
Simple approximate analytical expressions for the eigenvalues of anharmonic oscillators and confining potential models
Authors: Fernández Francisco M. , Castro Eduardo A.
Published: February 2003

The scaling variational method is applied in order to obtain approximate analytical expressions for the eigenvalues of anharmonic oscillators and confining potential models.
Total energy of heavy positive ions especially near the weak ionization limit
Authors: Grout P. J. , March N. H. , Tal Y.
Published: February 2003

Results, both analytical and numerical, for the total energy of heavy positive ions are presented. The q dependence of various energy-related quantities near the weak ionization limit (q → 0) is studied, q being 1−N/Z for N electrons and nuclear charge Ze.
Non-Markovian theory of activated rate processes. I. Formalism
Authors: Carmeli Benny , Nitzan Abraham
Published: February 2003

The escape of a particle from a potential well is treated using a generalized Langevin equation (GLE) in the low friction limit. The friction is represented by a memory kernel and the random noise is characterized by a finite correlation time. This non-Markovian stochastic equation is reduced to a Smoluchowski diffusion equation for the action variable of the particle and explicit expressions are obtained for the drift and diffusion terms in this equation in terms of the Fourier coefficients of the deterministic trajectory (associated with the motion without coupling to the heat bath) and of the Fourier transform of the friction kernel. The latter (frequency dependent friction) determines the rate of energy exchange with the heat bath. The resulting energy (or action) diffusion equation is used to determine the rate of achieving the critical (escape) energy. Explicit expressions are obtained for a Morse potential. These results for the escape rate agree with those from stochastic trajectories based on the original GLE. Non-Markovian effects are shown to have large effects on the rate of energy accumulation and relaxation within the well.