bluuebunny/crossref_metadata_2025 huggingface dataset:
The high-resolution visible overtone spectrum of acetylenea)
Authors: Scherer G. J. , Lehmann K. K. , Klemperer W.
Published: February 2003

Direct, gas-phase overtone spectra of states corresponding to five and six quanta of C–H stretch have been obtained for four isotopically substituted acetylenes in the region 14 900–18 500 cm−1. Peak positions of individual rotation–vibration lines were determined to a precision of about 0.003 cm−1. A total of 39 bands are analyzed: 16 for 12C2H2; 14 for 13C2H2; five for 12C13CH2; and four for 12C2HD. The rotational structure of the bands is fit to a semirigid rotor Hamiltonian. However, the bands suffer from severe rotational perturbations, with typical matrix elements being on the order of 0.3 cm−1 or less. The error in the determined band origins varies between 0.001 and 0.1 cm−1, depending on the degree of perturbation. Precision rotational constants are also determined for the observed bands. The vibrational term values cannot be adequately explained in terms of the usual slightly anharmonic normal mode expansion. Even though acetylene represents an intermediate case between the local mode and normal mode limits, the simple local mode theory described by Child and Lawton [M. S. Child and R. T. Lawton, Faraday Discuss. 71, 273 (1981)] can be used to rationalize many aspects of the spectrum—e.g., the splitting of the states ‖005g011〉 and ‖005u011〉 is found to be only 0.44 cm−1. The intermediate character of acetylene is seen upon single deuterium substitution. The state corresponding to five quanta of 12C–H stretch shifts about 100 cm−1 to the blue, a result which is certainly anomalous from the point of view of intuitive local mode theory. The band origins for the observed Σ–Σ transitions for all four acetylenes studied are found to be in good agreement with the results of a recent variational calculation [L. Halonen, M.S. Child, and S. Carter, Mol. Phys. 47, 1097 (1982)]. It is also observed that the anharmonic shifts of the sequence band transitions are quite large—for the v=5 overtone band, the sequence bands are shifted 74 cm−1 fo the Πg bend and 39 cm−1 for the Πu bend.
Dynamic light scattering studies of protein solutions under high pressure
Authors: Nyström Bo , Roots Jaan
Published: February 2003

Dynamic light scattering measurements on bovine serum albumin (BSA) at pH=4.7 and ionic strength I≊0.12 M were carried out in the pressure interval 1–4000 atm and for concentrations ranging from 8–80 kg m−3. At moderate pressures the mutual diffusion coefficient D was found to decrease linearly with concentration, while at the highest pressures deviation from linearity was observed. For a given concentration, the value of D increases initially with pressure and passes gradually through a maximum; at higher pressures (above 1000 atm) D decreases with increasing pressure. The hydrodynamic radius, deduced from diffusion data extrapolated to infinite dilution, was observed to increase with pressure during the denaturation process (pressures above 1000 atm) of the protein. Upon releasing the pressure the return of D was not reversible.
Pure electronic, vibronic, and two-particle surface excitons on the anthracene crystal. II. Experimental study and analysis of the (0,1) region
Authors: Bernard J. , Orrit M. , Turlet J. M. , Kottis Ph.
Published: February 2003

In this second part, we present the experimental and theoretical study concerning vibronic surface transitions for the vibration modes 390 and 1400 cm−1. We begin by a theoretical discussion of the different limiting cases of exciton-vibration coupling. In the experimental part, evidence of the surface character for the observed structures in surface emission excitation spectra is provided by their shifts upon surface coating. A general smilarity of the surface states with the previously described bulk states, including a translational equivalence (δ̄=206 cm−1), is established. The observed structures are assigned to interacting single particle (vibron) resonances and two-particle bands. However, some slight discrepancies between surface and bulk band structures lead us to question the complete validity of their translational equivalence. Finally, our observations show that the surface two-particle excitation profile (peak shaped) is quite different from the surface two-particle absorption profile (stepwise threshold profile). We propose a model mechanism of the surface excitations relaxation which accounts qualitatively for this specific surface excitation profile.
Longitudinal diffusion coefficients and test of the generalized Einstein relation for Tl+ ions in Kr and Xe, Li+ in Kr and Xe, and Cl− in N2 a)
Authors: Thackston M. G. , Byers M. S. , Holleman F. B. , Chelf R. D. , Twist J. R. , McDaniel E. W.
Published: February 2003

Longitudinal diffusion coefficients are measured for Tl+ in Kr and Xe, Li+ in Kr and Xe and cl− in N2. These diffusion coefficients are compared with the calculated ones from a previous measurement of ion mobility values.3 (AIP)
An improved approximate energy formula for molecules in terms of corrected free atom energies
Authors: Castro Eduardo A. , Fernández Francisco M.
Published: February 2003

A new approximate energy formula for molecules is presented. The relationship is based on corrected free atom energies. The correction factor reflects the change in the electrostatic potential at the nucleus of the atom in going from the free state to the molecule. Numerical testing shows a very good agreement with HF–SCF data as well as with other similar approximate formulas. (AIP)
Hypervirial calculations of Morse oscillator matrix elements
Authors: Requena A. , Peña R. , Zúñiga J.
Published: February 2003

MAtrix elements of the Morse oscillator are obtained in an efficient and quick way by using hypervirial relationships to generate a recursion formula to calcuate the matrix elements. (AIP)
Comment on ‘‘Hypervirial calculations of Morse oscillator matrix elements’’
Authors: Huffaker J. N.
Published: February 2003

The recursive method of Requena, Rena, and Zuniga1 for calculating the matrix elements of the Morse oscillator is criticized. The formula is considered not suitable for numerical computations. (AIP)
The low-lying 2Σ− states of OH
Authors: van Dishoeck Ewine F. , Langhoff Stephen R. , Dalgarno A.
Published: February 2003

Potential energy curves for the two lowest 2Σ− states of OH are computed at the configuration-interaction level using four different basis sets. Electronic transition dipole moments connecting the excited 1 2Σ− and 2(D)2Σ− states with each other and with the ground X 2Π state are presented as functions of internuclear distance. The theoretical absorption oscillator strengths for the D 2Σ−(v′=0) ← X 2Π(v″=0) transition are in good agreement with the empirical value derived from astronomical measurements. The photodissociation cross sections for absorption from the v″=0, 1, and 2 levels of the ground state into the continuum of the 1 2Σ− state are calculated, and the interstellar and cometary photodissociation rates are derived.
An improved self-interaction-corrected local spin density functional for atoms
Authors: Harrison Joseph G.
Published: February 2003

The application of the self-interaction-corrected local spin density approximation (SIC-LSDA) to atoms is reexamined. It is shown that a more careful application of the central-field approximation results in a modified functional which yields accurate total energies, correlation energies, and, in the ‘‘exchange-only’’ (X-O) version, exchange energies in good agreement with Hartree–Fock (HF) values. It is also shown that the X-O version of the earlier SIC-LSDA functional yields total energies in close agreement with experiment for second-row atoms. The proposed modification removes this tendency of the X-O functional to mimic a correlated functional.
A theoretical study on the mechanism of electronic to vibrational energy transfer in Hg(3P)+ CO collisions
Authors: Kato Shigeki , Jaffe Richard L. , Komornicki Andrew , Morokuma Keiji
Published: February 2003

The mechanism of electronic-to-vibrational (E–V) energy transfer in Hg(3P) + CO collisions has been studied theoretically. The configuration interaction (CI) method was employed to calculate potential energy surfaces of the collision system. A simplified theoretical model, based on the reaction coordinate concept and the calculated potential energy characteristics, was used to discuss the mechanism of the singlet–triplet transition and the energy disposal in the collision. The results obtained were that: (a) the quenching process proceeds via a collision complex mechanism; and that (b) the triplet–singlet transition occurs near the collinear geometry. A model classical trajectory calculation gives a product CO vibrational distribution in good agreement with the experimental result.
Equation of state for fluid hydrogen-isotopes H2, D2, and T2 up to their freezing points at 300 K
Authors: Shimizu Hiroyasu , Kumazawa Takao
Published: February 2003

The calculations of the P-V isotherms of fluid hydrogen isotopes H2, D2, and T2 up to their freezing pressures around 55 kbar at 300 K have been performed by using the modified hard-sphere variational perturbation theory with a quantum correction for four kinds of intermolecular potentials. The results by the use of the potentials of Silvera-Goldman and Nellis et al. agreed well with the experimental equation of state. The quantum pressures (ΔP) were estimated as a function of volume for H2, D2, and T2 at 300 and 200 K, and the dependences of ΔP on volume, molecular mass, and temperature were discussed.
Anisotropic rotational diffusion of an α helix and analysis of the internal motion of side chains
Authors: Hanssum H. , Rüterjans H.
Published: February 2003

In order to investigate the anisotropic rotational diffusion of the backbone and the side chains of poly-L-lysine the 13C spin-lattice and spin–spin relaxation times of all carbon atoms with directly bound H atoms have been obtained at a Larmor frequency of 67.89 MHz. The polypeptide was dissolved in a mixed solvent of 40% methanol and 60% water. In this solvent, at pH=11.3, the backbone of poly-L-lysine is in the conformation of an α helix with partially charged side chains. The macromolecule was, therefore, regarded as a rigid rod and the rotational diffusion of the backbone was described by two diffusion constants D1 and D3 which characterize the rotational diffusion of, and around, the symmetry axis, respectively. The rotational motion of the Cβ methylene group with respect to the laboratory coordinate system is characterized by the rotational diffusion of the backbone relative to the laboratory system and by superposed rotations around the Cα–Cβ bond relative to the molecular coordinate system. Simulation of the possible internal motions by using a molecular model has shown that only two rotameric positions of the β methylene group are allowed. Consequently, the model of jumps between two allowed rotamers was applied in the evaluation procedure. The corresponding theory of spin-relaxation was evaluated using Wigner rotation matrices. The diffusion constants of D1=1.0×105 s−1, D3=3.8×107 s−1, and the jump rate of k1=5.0×107 s−1 were evaluated. The rotations of the CγH2, CδH2, and CεH2 methylene groups have been described with the model of one-dimensional diffusion around the corresponding bonds.
The influence of protein dynamics on Mössbauer spectra
Authors: Knapp E. W. , Fischer S. F. , Parak F.
Published: February 2003

Protein dynamics gives rise to characteristic changes in a Mössbauer spectrum. The spectra are analyzed by a minimum of three Brownian oscillator modes accounting for protein specific motion probed by the Mössbauer nucleus. Two of these modes are extremely overdamped; a third mode has a diffusionlike character. The drastic changes of the Mössbauer spectrum with temperature are simulated by an extended version of the Brownian oscillator. With this oscillator the protein is characterized by conformational substates and transition states. The first are responsible for the solidlike, the latter for the liquidlike behavior of the protein. The interplay of transition states and conformational substates is responsible for largely different temperature dependences of the mean square displacements from x-ray and Mössbauer experiments.
The generalized Carnot cycle: A working fluid operating in finite time between finite heat sources and sinks
Authors: Ondrechen Mary Jo , Rubin Morton H. , Band Yehuda B.
Published: February 2003

The production of work in finite time from a reservoir with finite heat capacity is studied. A model system, for which the only irreversibilities result from finite rates of heat conduction, is adopted. The maximum work obtainable in finite time from such a system is derived, and is found to be strongly dependent upon the reservoir heat capacity. The cycle producing the maximum work is derived for an arbitrary one-component working fluid; no equation of state is assumed. In the optimum cycle, when the working substance is in contact with a finite reservoir, then the temperature of the working fluid is an exponential function of time and the entropy of the working substance is a linear function of time. While the maximum work obtainable in a single fixed-time cycle is a strictly increasing function of the reservoir heat capacity, the efficiency (work produced/heat put in) is a strictly decreasing function of the reservoir heat capacity, for the model system with a finite hot reservoir and an infinite cold reservoir. In the limit where the reservoir heat capacity approaches infinity, the finite-time efficiency approaches the Curzon–Ahlborn efficiency η=1−(T0low/T0high)1/2 for the cycle which produces maximum power.
Nuclear magnetic relaxation study of fully deuterated sulfolan
Authors: Peemoeller H. , Sharp A. R. , Watton A. , Kydon D. W.
Published: February 2003

Molecular motions of the fully deuterated sulfolan molecule (C4D8O2S) have been studied in the solid state by NMR measurements of the deuteron spin-lattice relaxation times in the laboratory (T1) and rotating (T1ρ) frame. In the crystalline phase, it has been found that the relaxation is determined by the ring puckering motion of the molecule. The plastic crystal phase is found to exhibit effects from both isotropic reorientation and translational diffusion. The modified nature of this phase and the plastic–crystalline transition of the deuterated as compared to the undeuterated solid is discussed in terms of the C–H—O hydrogen bonding between molecules.
Two-dimensional deuterium NMR of lipid membranes
Authors: Müller Luciano , Chan Sunney I.
Published: February 2003

The intrinsic linewidths of deuterium resonance in randomly oriented solids or liquid crystals can be extracted from two-dimensional NMR spectra in which spectral dispersion due to the quadrupolar Hamiltonian is removed in the indirectly detected frequency domain ω1. Such spectra can be obtained with a modified quadrupolar echo sequence in which the interval between the excitation and echo radio frequency pulse is rendered the second time variable. With this method, deuterium NMR linewidths have been measured in two model bilayer membranes as a function of temperature: 1-myristoyl-2-myristoyl-d27-phosphatidylcholine and a 3:2 1-palmitoyl-2-palmitoyl-(16,16,16)-d3-phosphatidylcholine:cholesterol mixture.
Imbedded matrix Green’s functions in atomic and molecular scattering theory
Authors: Lill J. V. , Schmalz T. G. , Light J. C.
Published: February 2003

This paper presents a general, simple, and unified treatment of Green’s function approaches to the solution of the sets of coupled second order differential equations encountered in the theory of inelastic and reactive scattering. The standard scalar theory of Sturm–Liouville problems is extended to systems of equations without recourse to spectral resolutions of the Green’s operator. A nonstandard approach to invariant imbedding is then developed to yield the most general kind of recursion relation for Wigner R matrices possible; the R-matrix propagation of Light and Walker and the variable interval-variable step algorithm of Parker, Schmalz, and Light are shown to be particularly simple examples of this more general scheme. Extensions and simplifications are offered. Also recurrence relations, stabilization of solutions, adiabatic and diabatic representations, and the use of nonorthogonal bases are all treated in a transparent manner.
Exact scattering solutions in an energy sudden (ES) representation
Authors: Chang B. , Eno L. , Rabitz H.
Published: February 2003

In this paper, we lay down the theoretical foundations for computing exact scattering wave functions in a reference frame which moves in unison with the system internal coordinates. In this frame the (internal) coordinates appear to be fixed and its adoption leads very naturally (in zeroth order) to the energy sudden (ES) approximation [and the related infinite order sudden (IOS) method]. For this reason we call the new representation for describing the exact dynamics of a many channel scattering problem, the ES representation. Exact scattering solutions are derived in both time dependent and time independent frameworks for the representation and many interesting results in these frames are established. It is shown, e.g., that in a time dependent frame the usual Schrödinger propagator factorizes into internal Hamiltonian, ES, and energy correcting propagators. We also show that in a time independent frame the full Green’s functions can be similarly factorize. Another important feature of the new representation is that it forms a firm foundation for seeking corrections to the ES approximation. Thus, for example, the singularity which arises in a conventional perturbative expansions of the full Green’s functions (with the ES Green’s function as the zeroth order solution) is avoided in the ES representation. Finally, a number of both time independent and time dependent ES correction schemes are suggested.
Reaction of ketenes with atomic oxygen
Authors: Washida Nobuaki , Hatakeyama Shiro , Takagi Hiroo , Kyogoku Takeshi , Sato Shin
Published: February 2003

Rate constants for the reaction of atomic oxygen with ketene, and methyl, ethyl, and dimethyl ketene were measured over a temperature range of 230–449 K using the pulse radiolysis resonance absorption system. Over the temperature range of the experiments, the rate data could be fitted by Arrhenius expressions: O+CH2CO, (2.92±0.78)×10−12exp[(−1349±154 cal mol−1)/RT]; O+(CH3)CHCO, (4.79±1.31)×10−12exp[(494.9±163.2 cal mol−1)/RT]; O+(C2H5)CHCO, (5.36±0.83)×10−12exp[(444.6±94.0 cal mol−1)/RT]; O+(CH3)2CCO, (5.92±0.94)×10−12exp[(1131±85 cal mol−1)/RT]; in units of cm3 molecule−1 s−1. The rate constants at room temperature were also determined using a discharge-flow system coupled to a photoionization mass spectrometer. Rate constants obtained are 0.043±0.04, 1.16±0.13, 1.36±0.11, and 6.04±0.64×10−11 cm−3 molecule−1 s−1 for CH2CO, (CH3)CHCO, (C2H5)CHCO, and (CH3)2CCO, respectively. Several reaction products were analyzed by the photoionization mass spectrometer.
Raman investigation of the effects of torsion on fused silica optical fibers
Authors: Hokmabadi M. S. , Walrafen G. E.
Published: February 2003

The application of reversible tensile stress to a pure fused silica optical fiber produces a significant modification of the Raman spectrum. The changes in Raman spectra are studied for fused silia optical fibers for applied reversible torsion. (AIP)
Supercritical extraction at atmospheric pressures
Authors: Procaccia Itamar , Gitterman Moshe
Published: February 2003

It is shown that solubility of solids in binary mixtures increase substantially near the liquid–liquid critical points. This allows supercritical extraction to be performed at atmospheric pressures rather than at the high pressures that characterize liquid–gas critical points.
Comment on ‘‘Recent determinations of potassium ion–rare gas potentials’’
Authors: Budenholzer F. E. , Gislason Eric A. , Jorgensen A. D.
Published: February 2003

Recent scattering measurements of the K+–gas potentials by the authors are compared with two new determinations of these potentials. The first is a theoretical calculation using an electron gas model, and the second utilizes a direct inversion proceduce in conjunction with measurements of ion mobilities. The overall agreement is good, but thers is a significant disagreement in the K+–Ar system between the scattering and mobility results.
On the kinetics of luminescence quenching in micellar systems
Authors: Tachiya M.
Published: February 2003

The kinetics of luminescence quenching in micellar systems as presented by Infelta, gratzel and Thomas is found to contain logical errors. Their treatment is further discussed and evaluated. (AIP)
The calculation of diamagnetic susceptibilities from the Thomas–Fermi–Amaldi theory of atoms
Authors: Donnamaria Maria C. , Castro Eduardo A. , Fernández Francisco M.
Published: February 2003

The importance of the Fermi–Amaldi correction for the Thomas–Fermi theory of atoms is re-examined with respect to a recent work [P. Csavinszky, Int. J. Quantum Chem. 15, 511 (1979)]. The calculated values of diamagnetic susceptibilities show an improvement over values determined from the Thomas–Fermi theory.
Scaled diatomics-in-molecules (SDIM) theory. I. General theory and preliminary applications to H3 and H4
Authors: Ellison Frank O.
Published: February 2003

Diatomics-in-molecules (DIM) is an established semiempirical theory for calculating atomization energies and potential energy surfaces for polyatomic systems in ground and excited states. A fundamental deficiency of this method must be considered its omission of optimum scaling of the diatomic and polyatomic wave functions. A new scaled DIM (SDIM) theory is proposed which utilizes a basis of scaled exact atomic state eigenfunctions. Scaled atoms-in-molecules (SAIM) theory [Theor. Chim. Acta 51, 241 (1979)] is employed to generate approximate optimumly scaled diatomic fragment eigenfunctions. Rigorous theory is formulated for independent variational scaling of polyatomic state functions using established DIM algorithms. Polyatomic eigenvalue equations are solved in terms of diatomic and monatomic eigenvector and empirical eigenvalue input; no complex electronic integral computations are required, except for overlap (as in ordinary DIM theory) and kinetic energy integrals. Initial applications to H3 and H4 using a minimal basis set are reported.
Structural studies of low temperature ice Ih using a central force potential model
Authors: Deutsch Peter W. , Hale Barbara N. , Ward Richard C. , Reago Donald A.
Published: February 2003

The revised central force potentials of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] are used to study the binding energy, structure, and multipole moments of a periodic ice Ih sample with a unit cell of 192 water molecules. The initial configuration for the unit cell has each oxygen in a wurtzite structure and intramolecular H–O–H angles symmetrically positioned in the tetrahedral O–O–O angles. Hydrogens are placed such that the total dipole moment for the unit cell is zero and the diagonal quadrupole moments are small (≲ 10−28 esu cm2). Subject to these restrictions, a static energy minimization on the periodic ice crystal yields an optimal O–O separation, intramolecular O–H distance, and intramolecular H–O–H angle of 2.78, 0.972 A, and 101.0°, respectively. Starting from this idealized wurtzite configuration, Metropolis Monte Carlo runs on the periodic system are made at 20 and 200 K. At 20 K, the equilibrated system has an average intermolecular potential energy per molecule of -15.2 kcal/mol and structure factors which have decreased to about 80% of the initial values. The dipole moment for the unit cell is ≂ 3 D. The equilibrated system at 200 K appears to be modified only by temperature dependent vibrational effects.
Mesoscopic kinetic theory
Authors: Grmela Miroslav , Laidlaw William G.
Published: February 2003

Kinetic theory is regarded as a phenomenological theory of macroscopic physical systems. The kinetic equations are constructed as continuity (Liouville) equations corresponding to the time evolution equations of a representative particle subjected to averaged, effective forces. Through the effective forces the unique character of the systems under consideration is expressed. The phenomenological kinetic theory is validated by establishing its relationship to equilibrium thermodynamics and hydrodynamics. A unified approach to the study of relations among dynamical theories formulated on different levels is proposed.
A dielectric model for the solvent effect on the intensity of light absorption
Authors: Shibuya Tai-ichi
Published: February 2003

A new dielectric model is proposed for the solvent effect on the absorption intensity. The ratio of the apparent oscillator strength f″ of a solute molecule measured in a solution of refractive index n to the oscillator strength f of the solute molecule is given by f″/f=[s(n2−1)+1]2/n, where s is a ‘‘shape’’ parameter of the cavity in which the solute molecule is supposed to lie. The parameter s is identified with the depolarization factor of a dielectric in the same shape as the cavity, for the direction of the transition moment. The proposed linear relation between (nf″)1/2 and n2−1 is demonstrated for the π → π* transition of β-carotene and for the n→ π* transition of pyrazine. For the allowed π → π* transitions of long linear polyenes, the s value is approximately 0, leading to the relation f″/f=1/n. The proposed formula also reduces to the well-known Chako formula f″/f=(n2+2)2/(9n) for the spherical cavity whose s value is 1/3. The theory predicts that 1/n≤f″/f≤n3. It is shown that the proposed formulas are also derivable from Scholte’s expressions of the cavity field and the reaction field for ellipsoidal cavity.
A pseudoatom theory for the liquid–vapor interface of simple metals: Computer simulation studies of sodium and cesium
Authors: D’Evelyn Mark P. , Rice Stuart A.
Published: February 2003

This paper describes a theory of the structure of the liquid–vapor interface of simple metal. The atomic motion is described by an effective Hamiltonian for the ions in an inhomogeneous metal. The ‘‘pseudoatom’’ Hamiltonian is derived by evaluating the electronic free energy of the metal to second order in the electron–ion pseudopotential. The model is completed by an approximate treatment of the metal–nonmetal transition which must occur in the traversal of the liquid–vapor interface. Using the derived effective Hamiltonian, Monte Carlo simulations of liquid sodium and cesium have been carried out. The Monte Carlo algorithm used is much more sophisticated than that employed in conventional simulations of liquids since the effective ion–ion interaction is density and position (relative to the surface) dependent, and therefore must be recalculated with each Monte Carlo displacement to insure convergence to a self-consistent effective Hamiltonian and density distribution. Monte Carlo simulations of bulk liquid sodium and cesium yield pair correlation functions which are in excellent agreement with experimental data. The simulations of the liquid–vapor interface reveal considerable structure, in the form of stable density oscillations extending several atomic layers into the bulk liquid; the spacing characteristic of this structure is about one atomic diameter. The existence of this ordering is traced to the variation in the surface zone of the so-called structure-independent energy component of the effective Hamiltonian. A less robust, more model dependent, result of the simulations is the prediction that there is a partial monolayer of ‘‘hybrid-state’’ species, neither metallic nor vaporized, adsorbed on the liquid metal surface. The existence of these hybrid-state atoms is a consequence of our treatment of the metal–nonmetal transition. The implications of our results for the interpretation of the surface properties of liquid metals are briefly discussed.
A uniform WKB approximation for spheroidal wave functions
Authors: Sink Michael L. , Eu Byung Chan
Published: February 2003

Uniform WKB wave functions are developed for prolate spheroidal wave functions which arise when the Schrödinger equation is given in prolate spheroidal coordinates. A detailed numerical test is presented for angular spheroidal wave functions. It shows that the approximate uniform WKB wave functions are excellent in accuracy.
Initial states of maximal entropy in formal scattering theory
Authors: Pfeifer P. , Levine R. D.
Published: February 2003

For a precollision state which is not sharply defined, not all details of the dynamics can be obtained by examination of the final state. A version of formal collision theory which takes full advantage of the inherent loss of detail is provided. Only the relevant aspects of the dynamics need then be computed and an explicit identification of the relevant details is provided by a generalized intertwining theorem. Several explicit examples where this point of view can be implemented are worked out.
The state-selective reactions of vibrationally excited CH (X 2Π) with oxygen and nitrogen
Authors: Duncanson John A. , Guillory William A.
Published: February 2003

The reaction rate constants for the reaction of CH (X 2Π, v″=0,1) with O2 and N2 have been measured. CH was produced by IR multiple photon dissociation of methanol and probed by laser induced fluorescence of the A(0,0) (431 nm) and A(0,1) (488 nm) transitions. The second order rate constants are k02 (v″=0)=2.1×10−12 cm3 molecule−1 s−1, k02 (v″=1)=4.3×10−12 cm3 molecule−1 s−1, kN2 (v″=0)=7.1×10−14 cm−3 molecule−1 s−1, and kN2 (v″=1)=3.0×10−12 cm3 molecule−1 s−1. The rate constants for CH (v″=1) are the observed combined rate constants for reaction and vibrational relaxation.
An analysis of the density dependence of the butane isomerization rate
Authors: Evans G. T.
Published: February 2003

A Fokker–Planck (FP) and a BGK-like collision operator are used in the analysis of the torsional dynamics of butane. Using previously derived kinetic equations, we have determined the torsional correlation time τ as a function of the density (or friction). The inverse of the torsional correlation time, or the isomerization rate, goes to zero at low density, reaches a maximum at an intermediate density, and decreases monotonically for higher densities. Predictions of the FP and BGK-like theories of the isomerization correlation time agree with the classic Chandrasekhar–Kramers result at high to moderate densities, and with stochastic molecular dynamics calculations of Montgomery, Holmgren, and Chandler.
Laser studies of electronic energy transfer in atomic copper
Authors: Chen Hao-Lin , Erbert Gaylen
Published: February 2003

Laser-induced fluorescence and crossed-beam optical pumping and probing techniques were used to study the cross sections of collisional mixing deactivation of electronically excited copper atoms (2P3/2, 2P1/2, 2D3/2, and 2D5/2) in various buffer gases. The cross sections for total deactivation of metastable status (2D5/2, and 2D3/2) to the ground state by the collision partners He, Ne, Ar, H2, D2, and N2 at 1450 °C are less than 10−20 cm2. Cross sections for the collisional mixing of 2D5/2 and 2D3/2 levels are more than an order of magnitude larger. However, collisional mixing of the 2P3/2 and 2P1/2 levels by the buffer gases does take place more rapidly with cross sections in the range of 10−16 cm2. The cross sections for total deactivation of Cu(2D5/2) to ground state, collisional mixing of the 2P3/2,1/2 levels, and collisional mixing of the 2D5/2,3/2 levels by atomic Cu at 1450 °C are 4.8×10−17, 8.7×10−15, and 1.7×10−15 cm2, respectively.
Geometric model of trapped electrons in trehalose single crystals x-ray irradiated at 3 K. An EPR studya)
Authors: Samskog P.-O. , Kispert L. D. , Lund A.
Published: February 2003

Three different radicals were identified by EPR in x-ray irradiated single crystals of trehalose at 3 K. The species are the trapped electron, a hydroxy alkyl radical, and an alkoxy radical. The electron is trapped in an intermolecular site formed by two hydroxyl groups, one on the carbohydrate and the other on a water molecule as evidenced by the anisotropic proton hyperfine couplings. A geometric model for the trapping site is presented. The trapped electron decays by cleavage of an OH bond and the liberated hydrogen atom abstracts another hydrogen atom from an adjacent carbon atom forming a hydroxy alkyl radical. The site of the alkoxy radical has been identified. The primary reaction mechanism is discussed.
Dipolar correlation function and motional narrowing in finite two-dimensional spin systems
Authors: Korb J.-P. , Torney D. C. , McConnell H. M.
Published: February 2003

A statistical treatment is used to describe the dipole–dipole relaxation processes of spins S=1/2 diffusing on finite two-dimensional (2D) surfaces. This leads to a general expression for the dipolar correlation function G(τ) including pairwise autocorrelation and cross-correlation terms. We show that for a finite 2D planar surface, G(τ) decays faster than that for an infinite planar surface. For finite 2D planar surfaces, dipolar translational correlation times, τ̄c are expressed in terms of the diffusion coefficient, the distance of closest approach between spins, and the area of the surface. It is shown that there is rapid motional line shape narrowing for sufficiently small two-dimensional surfaces. The calculation of resonance line shapes for the infinite 2D surface is discussed, but remains an unsolved problem when the only relaxation processes are those that arise from intermolecular dipolar interactions.
Electron spin resonance of Gd3+ in triacetate tetrahydrates of Sm, Nd, Er, Y, Yb, and Dy
Authors: Misra Sushil K. , Bartkowski M. , Mikolajczak Pawel
Published: February 2003

An EPR study of Gd3+-doped single crystals of triacetate tetrahydrates of Sm, Nd, Er, Y, Yb, and Dy has been made in order to study the systematics of EPR spectra in these homologous isostructural hosts at various temperatures. The absolute signs of the spin Hamiltonian parameters are determined from intensities of lines at liquid helium temperatures. The parameters are evaluated using a rigorous least-squares fitting procedure. As far as the systematics of the parameters are concerned, it is found that while the parameter b22 varies linearly, the parameter b02 varies approximately linearly with the atomic radius of the host rare-earth ion. The EPR studies presented here suggest a monoclinic symmetry at the site of the rare-earth ions in the rare-earth triacetate tetrahydrate crystals investigated. As well, all rare-earth sites are found to be magnetically equivalent. The EPR data also suggest that the Nd host undergoes some structural change at about 238 K.
Temperature dependence of intermolecular vibrational energy transfer in the two-channel cyclopropane-1,1-d2 system. Neon bath gasa)
Authors: Krongauz V. V. , Rabinovitch B. S. , Linkaityte-Weiss E.
Published: February 2003

The competitive, two-channel cyclopropane-1, 1-d2 isomerization to propylene has been used for the study of the temperature dependence of vibrational energy transfer efficiency. This note reports work with Ne bath gas at 823 and 1050 K. The fall-off region was k/k∞≊0.01. The average amount of energy <ΔE≳ transferred per collision with Ne from activated cyclopropane-1, 1-d2 molecules declines with temperature rise, from 575 cm−1 at 823 K to 275 cm−1 at 1050 K. The relative efficiency of collisions β̄ω declines from 0.062 at 823 K to 0.012 at 1050 K.
Localized orbitals and the theory of separated pairs
Authors: Luken William L.
Published: February 2003

The relationship between the theory of separated pairs and localized molecular orbitals is examined by approximating the energy of a separated pair wave function as the sum of two terms. The first term determines a linear vector space similar to that spanned by the canonical SCF orbitals. The second term determines a basis for that space which corresponds to a localized representation of the wave function.
Thermodynamic perturbation theory for molecular liquid mixtures
Authors: Fischer Johann , Lago Santiago
Published: February 2003

A Weeks–Chandler–Andersen type perturbation theory for the Helmholtz energy of mixtures consisting of molecules with nonspherical cores is given. The correlation functions are obtained from a reference mixture of softly repulsive spherical particles. For that mixture the Percus–Yevick equation is solved with Baxter’s formalism. By a blip expansion a hard convex body system is determined for which the free energy is obtained from Boublík’s equation. For one-center Lennard-Jones liquids, the excess properties for mixtures agree with simulation results as good as those of the Baker–Henderson and the variational theory, while the pure substance properties are obtained better now. For mixtures of one-center and two-center Lennard-Jones liquids, the excess volumes and the excess enthalpies are given for argon/nitrogen and argon/oxygen after fitting the unlike pair interaction to the experimental value of the excess Gibbs energy. The results resemble those obtained from simpler theories, but discrepancies with respect to the reported experimental data remain.
HNC solution for the central force model for liquid water
Authors: Thuraisingham Ranjit A. , Friedman Harold L.
Published: February 2003

Beginning with the central force model for water introduced by Lemberg, Stillinger, and Rahman, the HNC approximation method has been used to calculate the atom–atom pair correlation functions of a state of liquid water. Although a stable and accurate solution to the HNC equation for the model is obtained using the Rossky–Dale algorithm, the structure and thermodynamics agree only crudely with the published molecular dynamics results for the same model and the same N, V, T state.
Infrared and Raman orientation correlation functions of the ν3 vibration of N2O mixed with rare gases
Authors: Dreyfus C. , Ouillon R. , Berreby L.
Published: February 2003

IR and Raman orientational correlation functions are obtained from the corresponding profiles of the ν3 band of N2O at near-identical experimental conditions. The influence of the leak of polarized light is estimated for Raman scattering. The experimental correlation functions corrected for hot bands, are compared to the usual theoretical rotational diffusion models. None of the models fits both the IR and Raman correlation functions. A very good agreement is observed with the Steele perturbation theory, which introduces as the only parameter the mean square torque exerted on the molecule by the medium.
Laser photoelectron spectroscopy of MnH− and FeH−: Electronic structures of the metal hydrides, identification of a low-spin excited state of MnH, and evidence for a low-spin ground state of FeH
Authors: Stevens Amy E. , Feigerle C. S. , Lineberger W. C.
Published: February 2003

The laser photoelectron spectra of MnH− and MnD−, and FeH− and FeD− are reported. A qualitative description of the electronic structure of the low-spin and high-spin states of the metal hydrides is developed, and used to interpret the spectra. A diagonal transition in the photodetachment to the known high-spin, 7Σ+, ground state of MnH is observed. An intense off-diagonal transition to a state of MnH, at 1725±50 cm−1 excitation energy, is attributed to loss of an antibonding electron from MnH−, to yield a low-spin quintet state of MnH. For FeH− the photodetachment to the ground state is an off-diagonal transition, attributed to loss of the antibonding electron from FeH−, to yield a low-spin quartet ground state of FeH. A diagonal transition results in an FeH state at 1945±55 cm−1; this state of FeH is assigned as the lowest-lying high-spin sextet state of FeH. An additional excited state of MnH and two other excited states of FeH are observed. Excitation energies for all the states are reported; vibrational frequencies and bond lengths for the ions and several states of the neutrals are also determined from the spectra. The electron affinity of MnH is found to be 0.869±0.010 eV; and the electron affinity of FeH is determined to be 0.934±0.011 eV. Spectroscopic constants for the various deuterides are also reported.
IR-spectroscopic study of isotope effects on the NH/ND-stretching bands of meso-tetraphenylporphine and vibrational hydrogen tunneling
Authors: Limbach Hans-Heinrich , Hennig Jürgen , Stulz Josef
Published: February 2003

The IR spectra of meso-tetraphenylporphine (TPP) dissolved in CCl4 have been measured in the NH and ND stretching band region as a function of isotopic substitution using a newly constructed vacuum IR cell. Thus, it was possible for the first time to localize the NH and ND stretching bands of TPP–HD, which are characterized by the wave numbers 3335 and 2493 cm−1. TPP–H2 and TPP–D2 were found to absorb at lower frequencies, namely 3318 and 2482 cm−1. The observation of this band shift allows one to identify the observed NH and ND stretching bands in TPP–H2 and TPP–D2. They arise from antisymmetric stretching vibrations, the symmetric bands being forbidden in the IR spectra. NH/ND stretching bandwidths of the order of 20 cm−1 were observed, which is unusually small for proton transfer systems. This observation further confirms our previous conclusions from the primary HH/HD/DD kinetic isotope effects on the tautomerism in this molecule, namely that the motion of the hydrogen atoms takes place in a coupled manner from discrete vibrational NH stretching levels without substantial coupling to the motion of heavy atoms. Since the symmetric NH stretching vibration has a higher frequency than the antisymmetric stretching vibration, the interaction between the two inner hydrogen atoms in TPP is repulsive.
The spectroscopy and single vibronic level fluorescence quantum yields of jet cooled trans-stilbene and its van der Waals complexes
Authors: Zwier Timothy S. , Carrasquillo M. Edwin , Levy Donald H.
Published: February 2003

This paper reports results on the spectroscopy and dynamics of trans-stilbene seeded in a supersonic free jet. The cooling provided by the expansion results in well-resolved vibronic structure near the origin. Fluorescence excitation spectra reveal two low frequency vibrational modes at 82 and 95 cm−1 above the origin. By 1800 cm−1 above the origin the discrete vibronic structure has given way to a continuous absorption which extends to 6200 cm−1 blue of the origin. The fluorescence excitation spectrum is combined with a direct absorption measurement in the jet using a Xe lamp in order to obtain SVL fluorescence quantum yields for the isolated trans-stilbene molecule. The fluorence quantum yields show no mode dependence, indicating that vibrational relaxation within the trans configuration is much faster than isomerization to the perpendicular configuration. Stilbene van der Waals complexes with helium and argon have been identified in fluorescence excitation spectra at higher nozzle backing pressures. Dispersed fluorescence spectra of these complexes place an upper bound on the stilbene-He binding energy in the excited state of 82 cm−1. Several features of the photodissociation of these complexes are discussed.
Theoretical study of the effects of vibrational-rotational interactions on the Raman spectrum of N2
Authors: Langhoff Stephen R. , Bauschlicher Charles W. , Chong Delano P.
Published: February 2003

A systematic study of the polarizability and polarizability derivatives of N2 is undertaken as a function of basis set and level of correlation treatment. The value obtained for the ratio of derivatives (re β′e/βe) of the polarizability anisotropy β=α∥−α⊥ is 3.15±0.2, which is larger than the two experimental estimates of 2.63±0.29 and 2.22±0.44.
Angle-resolved photoelectron spectroscopy of N2O measured as a function of photon energy from 14 to 70 eV
Authors: Carlson Thomas A. , Keller Paul R. , Taylor James W. , Whitley Timothy , Grimm Frederick A.
Published: February 2003

Angle-resolved photoelectron spectra have been taken of the first four bands of N2O, using photons from synchrotron radiation. From these data, the partial cross section and the angular distribution parameter β have been obtained over a range of photon energies from 14 to 70 eV for the first four valence orbitals: 2π, 7σ, 1π, and 6σ. Calculations, based on the multiple scattering Xα method, also have been performed to obtain the partial cross sections and β values for comparison with experiment. An important element in the understanding of these data is the presence of shape resonances particularly in the photoionization of the 7σ and 6σ orbitals. Although the calculations are not in good quantitative agreement with experiment, they are able qualitatively to give a correct account of the overall behavior. In the case of the photoelectron spectra of the 7σ and 6σ orbitals, the vibrationally resolved bands were studied independently, particularly for their β values. Evidence of autoionization was found from detailed study of data on the 7σ orbital. In addition, marked changes in β over the vibrational envelope have been noted and possible explanations are advanced based on the effects of shape resonances and vibronic coupling.
Spectroscopy of the transition state. II. F+Na2→FNaNa‡*→NaF+Na*
Authors: Arrowsmith P. , Bly S. H. P. , Charters P. E. , Polanyi J. C.
Published: February 2003

Chemiluminescence from the reaction F+Na2→NaF+Na* (3 2P) has been studied in crossed uncollimated beams at a reagent pressure of ∼10−5 Torr, with systematic variation of experimental conditions. The atomic D line emission is accompanied by ‘‘wing’’ emission extending over several hundred angstroms, to either side of the D line. The source of the wing emission has been examined in some detail. The earlier proposal [J. Chem. Phys. 73, 5895 (1980)] that the wing comprises the emission spectrum of transition states FNaNa‡* which exist as the reaction products are in the process of separating, is in best accord with the observations. The kinetics, spectral shape, and intensity of the wings provide the principal clues as to their origin. The red and blue wings differ in shape. The integrated intensity in the red is approximately twice that in the blue. Alternative models are considered.
Negative ion photodetachment and the electron effective mass in liquids
Authors: Baird James K.
Published: February 2003

The electron photodetachment cross section for a negative ion in the gas phase is compared with the photodetachment cross section for the same ion when it is dissolved in a liquid supporting ‘‘free’’ electron propagation. The ratio of the amplitudes of these two cross sections near threshold is found to depend upon the effective mass m* of an electron in the conduction band of the liquid. We apply this result to electron photodetachment from O−2. In terms of the electron’s free mass m, we find for liquid argon at 87 K (m*=0.26 m), 2,2-dimethylbutane at 296 K (m*=0.27 m), 2,2,4-trimethylpentane at 296 K (m*=0.27 m), and tetramethylsilane at 296 K (m*=0.27 m). At 200 K, the effective mass in tetramethylsilane decreases to m*=0.21 m. In the case of liquid argon, the effective mass calculated herein agrees qualitatively with values which can be estimated from measurements of the electron mobility and exciton spectrum.
Kinetics of phase transitions: Theory of Ostwald ripening
Authors: Marqusee J. A. , Ross John
Published: February 2003

A new derivation is presented for the last stage of phase separation in the kinetics of a first order phase transition, precipitation, where Ostwald ripening is the dominant mechanism. We use a time scaling technique and derive the power law time dependence and distribution function for the size of the particles of the new phase. Equations are derived for the correction terms to the distribution function and power laws. The derivation clarifies and corrects prior work.