bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Intramolecular Relaxation Processes
Authors: Hofacker G. Ludwig
Published: January 2005

A master equation is derived to describe internal relaxation processes in molecular systems with a relatively small number of degrees of freedom. It is an inhomogeneous equation, taking into account nondiagonal elements of the coarse-grained density matrix which prove to be the most relevant ones for the problem under consideration. Various relaxational time scales, inherent in a molecular system, can thus be shown to exist. Relaxation mechanisms and equilibrium states on these time scales can be determined. The general character and different types of solutions of the master equation are investigated. The theory is applied to internal vibrational relaxation and intramolecular rearrangement (isomerization) reactions.
Some Recent Developments in the Quantum-Mechanical Studies on the Electronic Structure of the Nucleic Acids
Authors: Pullman Bernard
Published: January 2005

The molecular orbital method has been used both in the Hückel and in the self-consistent-field approximation for the determination of the principal indices of the electronic structure of the purine—pyrimidine pairs of the nucleic acids. Both approximations lead to substantially the same conclusions insofar as the general aspects of the results are concerned. Special attention is being paid to the factors presumed to be responsible for the stability of the double-stranded structure of DNA, and in particular for the greater stability of the nucleic acids rich in guanine—cytosine over those rich in adenine—thymine. This last situation is shown to result from the greater in-plane resonance stabilization through hydrogen bonding of the G—C pair than of the A—T pair and the greater vertical interaction energy between neighboring G—C pairs than between neighboring A—T pairs due to the greater tendency of the G—C pairs to charge-transfer complexation and to their greater contribution to the van der Waals—London interaction energies. The intercalation of aminoacridines is shown to confirm different aspects of the theoretical results. Calculations of the van der Waals—London interaction energies are also carried out for the stacking association between free purines and pyrimidines in solution and for similar associations between the purines and aromatic hydrocarbons. In this last case the extent of association is determined essentially by the dispersion forces. The relation of this result to chemical carcinogenesis is discussed. Results of calculations on dipole moments and ionization potentials of the purine and pyrimidine bases are described. The earlier predictions of the theory about the existence of some particularly good electron donors and acceptors among these compounds have been verified. The first ionization potential of the bases is predicted to be that of their π electrons.
On a Second-Order Thomas—Fermi Theory
Authors: Handler George S.
Published: January 2005

A second-order Thomas—Fermi theory, involving a product representation of the θ operator, has been constructed. It yields a particle density exhibiting a shell structure for the one-dimensional harmonic oscillator.
Projection Operators for Atomic and Molecular Problems
Authors: Handler George S.
Published: January 2005

An operator formalism is developed that allows full account of correlation to be taken in terms of a wavefunction with all interparticle coordinates. The operator is shown to be an eigenoperator of S2.
N-Representability Problem for Fermion Density Matrices. I. The Second-Order Density Matrix with N =3
Authors: Smith Darwin W.
Published: January 2005

The N representability problem is the problem of how to recognize whether a given pth-order reduced density matrix is derivable from an antisymmetaic N-particle wavefunction ψ by integrating out all but coordinates from ψ*ψ.

The conditions under which a given second-order density matrix is N representable by a three-particle wavefunction are discussed.
Molecular Orbital Theory and the Physical Properties of Molecules
Authors: Nesbet R. K.
Published: January 2005

In recent years, it has become possible to compute Hartree—Fock molecular orbitals for molecules more complex than H2. Qualitative implications of this quantitative work are discussed, with emphasis on the identification of electronic excited states, on molecular electric dipole moments, and on the net correlation energy contribution to molecular dissociation energies.
Electric Dipole Polarizability of Atoms by the Hartree—Fock Method. I. Theory for Closed-Shell Systems
Authors: Cohen Howard D. , Roothaan C. C. J.
Published: January 2005

A method for the calculation of the dipole polarizabilities of closed-shell atomic systems is presented. This method involves the direct calculation of the Hartree—Fock wavefunction of the atom in the presence of the perturbing field. The orbitals are expressed as linear combinations of Slater-type functions. A large number of carefully chosen and optimized basis functions are used so as to assure a good fit to the true Hartree—Fock wavefunction. The polarizability is then calculated from the limiting value of α=p/F for F=0, where F is the electric field strength, and p is the induced dipole moment.
Correlation Energy Calculation for the 1Σg+ Ground State of the Nitrogen Molecule
Authors: Grimaldi François
Published: January 2005

Starting from a molecular Hartree—Fock wavefunction an extensive configuration-interaction calculation (201 configurations) has been carried out for the 1Σg+ ground state of N2. The matrix elements of the electrostatic Hamiltonian were calculated automatically. Both Brillouin—Wigner and Rayleigh—Schrödinger perturbation expansions, carried to a sufficient order, are shown to be good tools to find the lowest eigenvalue and eigenvector of very large matrices. Fifty percent of correlation energy is attained by this exact treatment.

Since the second-order Rayleigh—Schrödinger perturbation expansions are a good approximation to the exact results, it supplies, in addition to a good test for the selecting of configurations, a practical means of evaluating pair correlations. By using this approximation and 3043 configurations, 66% of the correlation energy was found.
Approximate Natural Orbitals for Four-Electron Systems
Authors: Barnett Gene P. , Linderberg Jan , Shull Harrison
Published: January 2005

Approximate natural orbitals for four-electron wavefunctions for Be as calculated by Boys, Matsen, Watson, and Weiss and LiH as calculated by Ebbing are obtained by diagonalization of the appropriate first-order reduced density matrices. The formalism for carrying out the process is extended to the case of a nonorthogonal basis. Occupation numbers are presented and compared for the functions reported. In addition, truncated natural expansions reproducing the original functions are tabulated. Natural-orbital functions are tabulated. Natural-orbital occupation numbers, the orbitals themselves, and the natural expansions are shown to have considerable value in comparing these functions. The nature of the approximations used in the individual functions is clarified by the analysis, and considerable insight is afforded to the nature of the physical system.
Localized Atomic and Molecular Orbitals. II
Authors: Edmiston Clyde , Ruedenberg Klaus
Published: January 2005

Using a recently proposed procedure, the localized molecular orbitals are determined for minimal-basis-set LCAO—SCF wavefunctions of the molecules LiH, BH, NH, FH, Li2, B2, Be2, N2, F2, CO, BF, LiF. In all cases, well-defined inner-shell, lone-pair, and bond orbitals are found. They exhibit a considerable degree of transferability between different molecules, and the s-p hybridization varies regularly across the periodic table. In some cases the localized molecular orbitals deviate from accepted intuition; in all cases the exact determination of intrasymmetry localization is important. A close relation is found between the localized molecular orbitals and those molecular orbitals which extremize the MO-overlap populations. In the case of the HF molecule, the localized orbitals are also determined for the exact self-consistent-field wavefunction and, the transformation from canonical to localized molecular orbitals is found to be almost identical with that in the minimal-basis-set approximation. Implications of the localization procedures and its results are discussed.
Theoretical Studies of Two-Photon Absorption Processes. II. Model Calculations
Authors: Honig Barry , Jortner Joshua
Published: January 2005

Two-photon absorption cross sections are calculated for the hydrogen atom and the hydrogen molecule. Three methods of calculation are employed: (1) a second-order time-dependent perturbation expansion; (2) a ``mean-energy'' approximation; (3) a sum-rule equivalent of perturbation theory. The various methods are compared and evaluated in terms of their general utility in describing double-photon absorption processes.
Floating Spherical Gaussian Orbital Model of Molecular Structure. I. Computational Procedure. LiH as an Example
Authors: Frost Arthur A.
Published: January 2005

The Kimball—Neumark spherical Gaussian orbital model is extended to apply to the singlet ground states of the general molecule with localized orbitals. Formulas are presented for energy, electron density, dipole moment, and the forces on nuclei and the computational procedure is described. The model is applied to LiH and the results are discussed in detail.
Influence of Nonbonded Interactions on Molecular Geometry and Energy: Calculations for Hydrocarbons Based on Urey—Bradley Field
Authors: Jacob E. Jean , Thompson H. Bradford , Bartell L. S.
Published: January 2005

A modified Urey—Bradley potential energy function comprised of quadratic terms for bond stretches, bond-angle bends, and torsional displacements together with analytical expressions for pairwise nonbonded interactions was chosen to represent the force field for hydrocarbon molecules. Quadratic constants were taken from the spectroscopic U–B analyses of Schachtschneider and Snyder [Spectrochim. Acta 19, 117 (1963)], while the nonbonded functions adopted were those proposed by Bartell [J. Chem. Phys. 32, 827 (1960)]. Reference bond angles for the quadratic terms were taken to be 109.5° or 120° for tetrahedral or trigonal coordination, respectively. Reference single-bond lengths and the torsional constant were adjusted to fit the experimental data for CH4 and C2H6. Double bonds and ring bonds in cyclopropyl compounds were considered to be rigid. The above selections served to establish a universal model force field for hydrocarbons with no remaining adjustable parameters. The potential energy functions for a variety of saturated hydrocarbons and several olefins and cyclopropyl derivatives were minimized with respect to independent structure parameters (i.e., bond stretches, bends, and internal rotations). Even though all C–H (and C–C) bonds were input to be identical to those in CH4 (and C2H6) except for nonbonded environment, the bond lengths and angles corresponding to the minimum potential energy exhibited an appreciable variation from molecule to molecule, as did also the strain energies of geometric and rotational isomers. Calculated trends in structures, isomerization energies, and barriers to rotation agreed quite well with experimentally observed trends, provided that experimental isomerization energies were corrected to 0°K and zero-point energies were taken into account. Some novel features of the results and applications of the model for predicting deformations in strained systems are discussed. The present study differs from previous work in the area of ``molecular mechanics'' in the use of a more general force field, in allowing the strained molecules to relax in all degrees of freedom (except for unsaturated groups and cyclopropyl rings), in the selection of molecular systems, and in a detailed comparison with experiment.
Systematic Approximations to the Partition Function for Crystalline Solids
Authors: Beyerlein Adolph , Salsburg Zevi W.
Published: January 2005

The two-dimensional harmonic system based upon a triangular lattice with nearest-neighbor interactions only is used as a test case to compare several systematic approximation schemes for obtaining the partition function of a crystalline solid. Attention is focused on the high-temperature limit where the free energy function FN has the form FN/NkBT = −2lnT*+D. T* is a reduced temperature. Comparisons are made on the results obtained for the additive constant D. The various schemes examined are (1) a modified cell-cluster expansion, (2) a sequence of m×∞ strips, i.e., extended tunnel models, (3) extrapolation of the properties of m×m systems with fixed boundary conditions, and (4) extrapolation of the properties of m×m systems with periodic boundary conditions. The results demonstrate that a cell-cluster expansion through sixth order (i.e., including all six-particle figures) gives a better estimate of the free energy than a 10×∞ system, a 12×12 system under fixed boundary conditions, or an 11×11 system under periodic boundary conditions. The exact value of D to four significant figures was obtained by extrapolating the results of the m×m systems with periodic boundary conditions, and the result is 0.8256.
Rate of Attachment of Gaseous Electrons to Nitrogen Dioxide
Authors: Mahan Bruce H. , Walker Isobel C.
Published: January 2005

The rates of attachment of gaseous thermal electrons (300°K) to NO2 in the presence of several inert gases have been measured. In the pressure range from 3 to 70 mm, the rate of attachment is independent of the pressure, but dependent on the nature of the inert gas. A mechanism is proposed that accounts for these observations.
Matrix Elements for Configuration d4 in a Weak Octahedral Field Using Racah Methods
Authors: Dunn T. M. , Li Wai-Kee
Published: January 2005

Employing Racah algebra, the general formula for calculating the matrix elements of a weak crystalline field for configuration dn has been derived. Applying this formula the matrix elements for d4 (including spin—orbit coupling interaction) have been calculated and tabulated.
Electron Spin Resonance Studies of a Reaction Intermediate in Strontium Chloride
Authors: Catton R. C. , Harrison L. G.
Published: January 2005

The reaction of strontium chloride powder or single crystal with fluorine at room temperature produces a defect, stable after removal of fluorine but located close to the reaction interface only, which has an electron spin resonance absorption. The ESR spectrum is consistent with a model of the defect as a chlorine atom displaced from an anion site towards a neighboring anion vacancy. The principal directions of the hyperfine tensor and g tensor are two twofold axes and a fourfold axis of the SrCl2 crystal. The tensor components indicate that the unpaired electron is localized on the Cl atom, and suggest that the atom is subject to a strong crystal field determined chiefly by two nearest-neighbor cations which define a twofold axis of the crystal. The unpaired electron is in an orbital mainly of p character and aligned along a twofold axis which is probably the one perpendicular to the line of the cations. The single-crystal spectrum, although having orientation-dependent line positions, has line shapes and intensities resembling those of a powder spectrum. This suggests a range of relative displacements of Cl atom and neighboring cations along a ``reaction coordinate'' which is probably a fourfold axis of the crystal.
Mechanisms of Populating Electronically Excited CN in Active Nitrogen Flames
Authors: Iwai Tsuruji , Savadatti M. I. , Broida H. P.
Published: January 2005

CN red (A 2Π⇀X 2Σ) and violet (B 2Σ⇀X 2Σ) bands radiated from active nitrogen flames with halogenated hydrocarbons and with cyanogen derivatives have been studied at pressures from 0.013 to 100 torr. Intensity measurements have shown that there are three distinct vibrational population distributions P1, P2, and P3 in the A 2Π state and corresponding distributions P1′, P2′, and P3′ in the B 2Σ state of CN. At very low pressures, P1 distributions are characteristic of cyanogen derivative flames and P2 distributions are characteristic of halogenated hydrocarbon flames. P3 distributions are most easily observed at pressures above 1 torr and with trace amounts of fuels containing carbon. Three distinct mechanisms responsible for producing these three types of distributions are proposed; two mechanisms involve the transfer of energy derived from the recombination of atomic nitrogen and the third is a chemical reaction using atomic nitrogen. Vibrational relaxation is observed for the P2 and P1′ distributions. Small amounts of oxygen are found to increase greatly the CN emission at low pressures. Intensity measurements of rotational lines in the red bands and in the violet 0, 0 band have been made as a function of pressure in CH2Cl2 flames. In the A 2Π state at pressures above 4 torr, a rotational temperature of 340°K can be defined, but below 4 torr the rotational distribution is best represented by a sum of two Boltzmann distributions. The effect of pressure on the amount of CN in the two distributions leads to a measured cross section of 15 Å2 for the effective collisional relaxation of rotation. From a study of the violet 0, 0 band, several new pairs of rotationally perturbed lines are found at low pressures. The formation rate of the A 2Π state relative to the B 2Σ state and to the X 2Σ state is obtained from the intensity ratio of main lines relative to extra lines in rotational perturbed pairs. CN is found to be formed in the A 2Π state at least 30 times more readily than in the B 2Σ state and about four times faster than in the X 2Σ state.
Nonadiabatic Transitions in Solids
Authors: Osherov V. I.
Published: January 2005

A pair of interacting parabolic terms are considered. The terms are linearly coupled with a medium, which has a Debye spectrum of frequences. By the help of the model presented here it is possible to describe localized thermal transitions of electrons in imperfections. The relaxation equation describing the transition in the system is found by using time-dependent perturbation theory for interaction and coupling. The relaxation equation is solved approximately. It is shown that the nonadiabatic transition rate has a maximum as a function of the interaction with the medium. This effect may be observed experimentally.
N Representability of Fermion Density Matrices
Authors: Freed Karl F.
Published: January 2005

The proof of Smith, which gives the solution to the N-representability problem of the first-order density matrix for the case of N even and a nondegenerate energy eigenstate, is also shown to be valid for certain linear combinations of degenerate states. A connection is shown between these proper linear combinations and the eigenfuctions of a perturbed Hamiltonian for which all of the degeneracies have been lifted. For the case of S=0, all the eigenfunctions of the pth-order density matrix (natural p functions) can be taken to be eigenfunctions of total spin (Σ lim i=1pSi)2,and if orbital angular momentum is a constant of the motion, these natural p functions are eigenfunctions of the total orbital angular momentum for L=0. Simple wavefunctions are presented for which the natural 2 functions are not all eigenfunctions of the total pair spin. It is then shown that for MS=0 (any integral spin) or for L=1, ML=0, the natural 2 functions are eigenfunctions of (S1+S2)2 and (L1+L2)2, respectively.
Lower Bounds to Eigenvalues of the Schrödinger Equation. I. Formalism for Excited States
Authors: Wilson Timothy M.
Published: January 2005

A procedure is presented for the calculation of lower bounds to the excited states of a Hamiltonian of the type H=H0+V, where H is bounded below and self-adjoint, V is positive definite, and H0 has a known set of eigenfunctions. This procedure is derived using the partitioning technique. A detailed study is made into the effect that replacing the reaction operator t(ε) by its inner projection onto some linear manifold f has on the curves of the multivalued bracketing function. From this analysis it is shown for the first time that when the linear manifold, onto which the projection of t(ε) is made, is of the type f=t(ε)−1/2 (ε−H0) j, the bracketing curves are no longer monotonically descending when plotted as a function of ε. This result is very important in the calculation of lower bounds to excited states.
Lower Bounds to Eigenvalues of the Schrödinger Equation. II. Application to Helium and Li+
Authors: Wilson Timothy M. , Reid Charles E.
Published: January 2005

The procedure developed in the preceding paper is used to calculate lower bounds to some of the low-lying 3S levels of helium and Li+. These calculations are the first applications of the partitioning technique to the excited states of atoms. They are made using the manifolds f=t(ε)−1/2(ε−H0) j and f=t(ε)−1/2h to construct the inner projection t(ε)′. In the latter case, a truncated reduced resolvent T0(p) was used to approximate T0. The effect that these projections have on the curves obtained by plotting the multivalued function ε′1 as a function of ε for these two cases, is also presented. The results seem to indicate that the use of the former manifold to construct t(ε)′ leads to quite close bounds for the ground states but the projection constructed using the latter manifold is better for treating the excited states. The relationships between this method and other lower bound procedures are discussed.
Pi-Electron Hamiltonian
Authors: Harris Robert A.
Published: January 2005

A new pi-electron Hamiltonian is derived for planar conjugated molecules. The Hamiltonian includes the effect of dynamic screening of the pi electrons from one another by the sigma electrons, as well as the screening of the core. The method used in Van Vleck's method of unitary transformations.
Excluded-Volume Effects in Linear Polymer Chains: A Hierarchy of Differential Equations
Authors: Yamakawa Hiromi , Tanaka Genzo
Published: January 2005

A hierarchy of differential equations for the expansion factor of a linear polymer chain is derived in a purely formal way by successive differentiation of the general equation of Fixman with respect to the binary-cluster integral for a pair of chain segments. The hierarchy is truncated by a physically reasonable assumption to obtain an approximate solution. The assumption introduced is discussed in detail. In order to obtain numerical results, it is necessary to develop at least the third-order perturbation theory, and the third expansion coefficient is evaluated to be 6.459 for the mean-square end-to-end distance. Assuming that the third coefficients are the same for the end-to-end distance and the radius of gyration, there is obtained the equation for the expansion factor αS for the latter, αS2=0.541+0.459(1+6.04z)0.46, where z is the well-known excluded-volume parameter. Although this equation has the asymptotic form αS4.35=constant z at large z, a definite conclusion concerning the value of the exponent of αS cannot be drawn from the present formulation. From the above equation and the detailed analysis, however, it may be concluded that the correct values of αS must be between those predicted by the Flory theory and the Ptitsyn theory.
Lifetime of Excited States Producing Charge Carriers in Molten Aromatics
Authors: Baessler H. , Abt K. O.
Published: January 2005

Excitation of the lowest triplet state in molten naphthalene, pyrene, and anthracene gives rise to a photocurrent. The lifetime of the excited states responsible for charge-carrier formation is 250±50 msec for naphthalene, 40±10 msec for pyrene, and approximately 10 msec for anthracene. It is determined (i) from the time response of the photocurrent after starting and shutting off illumination, and (ii) from the time dependence of the photocurrent peak which is observed if the external voltage is applied with a certain delay time after shutting off illumination.
Some Hartree—Fock Results for Two- and Four-Electron Atomic Systems
Authors: Froese Charlotte
Published: January 2005

Some numerical Hartree—Fock results are reported for excited states of two- and four-electron atomic systems. Transition integrals are given and some oscillator strengths are compared with values obtained by other methods.
Molecular g Value, Magnetic Properties, and the Ground-State Electronic Structure of Fluoroacetylene
Authors: Weiss V. W. , Todd H. D. , Lo Mei-Kuo , Gutowsky H. S. , Flygare W. H.
Published: January 2005

The first-order molecular Zeeman effect observed in the J=0→J=1 rotational transition of FC≡CH gives the magnitude of the molecular g value perpendicular to the molecular axis to be 0.0071±0.0004. When combined with an estimate of the molar susceptibility, the molecular g value leads to an average value of r2 for electrons from the center of mass. The result is 〈ψ0|Σiri2|ψ0〉=37.9×10−16 cm2. An upper limit on the magnitudes of the proton and fluorine spin—rotation interaction constants of 6–8 kHz was established by high-resolution, microwave linewidth studies of the J=0→J=1 transition.

The ground electronic state of fluoroacetylene is described by a set of 11 hybrid molecular orbitals, employing various hybridization and ionic parameters. The average values of nine one-electron operators were calculated using the 16 atomic-orbital functions included in the minimal basis LCAO MO set. The Coulson—Barnett expansion technique was used in the calculation of the two- and three-center integrals. The calculations of the one-electron operators were made for considerable ranges in the adjustable parameters of the wavefunction.

A best-fit wavefunction was obtained by fitting six of the one-electron operators to the experimentally determined properties. It was then used to compute the average value of r2 and the H and F diamagnetic shielding. The latter are combined with available chemical-shift data to yield the H and F paramagnetic shielding and spin—rotation constants. The results for the spin—rotation constants are consistent with the upper limit established by the linewidths. Also, the theoretical value of r2 agrees very well with that determined experimentally. Several features of the electronic structure and ground-state wavefunction are discussed. For instance, we found negligible s character in the fluorine atomic orbitals participating in the F–C sigma bound but a significant fluorine contribution to the F–C pi bond.
Study of Some of the Parameters Affecting Knudsen Effusion. III. The Vapor Pressure of Gold
Authors: Ward John W.
Published: January 2005

Vapor-pressure data for gold were obtained during a study of the spatial distributions of molecular beams effusing from Knudsen cells. Even with such a simple, ideal substance, deviations from cosine behavior were noted. These deviations are attributed to geometrical effects arising from cell and sample configurations, and to losses within the cell. Knowledge of the causes and effects of these deviations allowed vapor-pressure data of high prescision to be obtained.
Conduction in Crystals Containing Hydrogen Bonds. I. KHF2 and KDF2
Authors: Pollock J. M. , Sharan M.
Published: January 2005

Direct current electrolysis measurements on solid KHF2 have shown that protons are mobile in the solid, and are liberated as hydrogen gas at the cathode. From the amount of gas evolved it has been concluded that all the current in the solid is carried by the protons. Alternating current conduction measurements have also been made on solid KHF2 and KDF2 at various temperatures. It has been found that in the α-phase region (below 196°C) the conduction follows an Arrhenius-type equation with an activation energy, E=21.7 kcal mole−1, and 23.5 kcal mole−1 for KHF2 and KDF2, respectively. A sharp discontinuity is observed in the conduction plots at the α—β transition, above which an Arrhenius relation is again obeyed with E=19.8 kcal mole−1 and 20.9 kcal mole−1 for KHF2 and KDF2. The suggested mechanism of conduction through the crystal is by migration of interstitial protons or ``proton defects,'' and it is suggested that the observed activation energies refer to the formation of these defects.
Excited States of Nucleotides and Singlet Energy Transfer in Polynucleotides
Authors: Guéron M. , Eisinger J. , Shulman R. G.
Published: January 2005

We have measured the absorption, fluorescence, and phosphorescence spectra of nucleotides at 77°K. The order of decreasing energies is A, U, T, G, C for the singlet, and U−, C, G, T−, A, T for the triplet. Besides the quantum yields of fluorescence and phosphorescence, we also determined the yield for intersystem crossing to the triplet, using the amplitude of the Δm=2 triplet ESR signal. We find internal conversion occurring from both the singlet and triplet states. From the excitation energies in the neutral and ionized molecules, the stability of the ionizable proton in the excited states can be compared to that in the ground state, and the results are applied to the question of proton transfer from T to A in DNA.

From a discussion of the various cases of intermolecular energy transfer for singlets, and considering the broadband spectra of the nucleotides, it is shown that Förster's ``very weak case'' is applicable. We emphasize that two subcases must be distinguished, depending on whether transfer occurs faster than, or slower than, vibrational relaxation. The justification of the approximations in our treatment is given in the Appendix.

Assuming dipole—dipole coupling, the rate of transfer is estimated in the nucleotides in the ``before relaxation'' subcase. In the ``after relaxation'' subcase the rate of transfer is calculated using the emission data obtained in this study. In a majority of the pairs of nucleotides, ``after relaxation transfer'' at the Watson—Crick distances is allowed. These considerations are discussed briefly in reference to transfer in polyadenylic acid and DNA.
Crystal Field in Rare-Earth Trichlorides. II. Exchange Charge Effects in PrCl3
Authors: Bishton S. S. , Ellis M. M. , Newman D. J. , Smith J.
Published: January 2005

The redistribution of charge due to overlap between the rare-earth ion 5s2p6 shell and the surrounding ligands and to overlap between neighboring ligands is shown to produce a large reduction in the electrostatic contributions to the crystal field. This correction brings the calculated value of A20〈r2〉 close to its experimental value in PrCl3.
Collision Broadening of Rotational Absorption Lines. II. Self-Broadening of Symmetric-Top Molecules
Authors: Murphy Joseph S. , Boggs James E.
Published: January 2005

A recently developed theory of the broadening of rotational absorption lines due to intermolecular collisions has been applied to available experimental data on CH3Cl, CH3F, CHF3, and PF3. It is shown that rotational energy transfer for these symmetric-top molecules is almost entirely dependent on dipole—dipole interactions, so their linewidths are calculable entirely from well-known molecular parameters resulting in a stringent test of the theory. The agreement, in general, is very satisfactory. Calculations are also presented based on earlier theoretical methods.
Studies on Rydberg Orbitals. I. Slater—Condon Parameters and Valence-State Energies for Rydberg Excitations Determined from Atomic Spectra of Be–F
Authors: Hosoya Haruo
Published: January 2005

The observed atomic spectral terms of 2sm2pn3l (m = 0, 1, 2; n = 0, 1, ···, 5; l = s, p, d) were analyzed for the isoelectronic series from Be I to F I. By use of graphical inspection for deleting the effects of configuration interactions, nine series of the Slater—Condon parameters pertinent to the Rydberg orbitals were obtained together with F2pp and G1sp. The selected values are tabulated, most of which are accurate enough to be compared with and criticized by the authentic values of F2pp and G1sp. It was shown from these observed parameters that the spatial distribution of the 2p (or 2s) electron in the 2sm2pn3l state is very close to the spatial distribution in the 2sm2pn state as implied in the Slater rule. The energy expressions for the terms of spml′ (m = 1, 2, ···, 5; l = s, p) configurations are given. With these F and G values, valence-state energies for Rydberg excitations were obtained.
Further Examination of the Reaction of Oxygen Atoms with Perfluoropropene
Authors: Heicklen Julian , Knight Vester
Published: January 2005

The reaction of oxygen atoms with C3F6 has been examined further, in both the presence and the absence of molecular oxygen, at room temperature and at 126°. The oxygen atoms were generated from the mercury-sensitized decomposition of N2O. Both (C3F6) and (O2) were varied by a factor of 10 and the lamp intensity by a factor of 200. In addition to N2, the products were CF2O, CF3CFO, C5F10[Complex chemical formula],and, in the presence of O2, C3F6O (perfluoropropylene oxide). The reaction scheme is analogous to that for C2F4 and is discussed in detail. A number of relative rate constants could be estimated, and they are tabulated. Important intermediates are CF2, CF3CF, and C3F6O* in the absence of O2, together with CF2O2 and CF3CFO2 in the presence of O2.
Paramagnetic Resonance Spectra of Se2− and SSe− in the Alkali Iodides
Authors: Vannotti L. E. , Morton J. R.
Published: January 2005

The impurity ions Se2− and SSe− have been introduced into NaI and KI and detected by their paramagnetic resonances. The g factors of these centers are highly anisotropic; in KI, for example, the principal g factors of Se2− are 3.7079, 0.7824, and 0.7698. The first of these corresponds to the Se–Se bond direction (z), which was found to be parallel to the {110} directions in the crystal. The direction of minimum g has been associated with the direction of the pπ orbitals occupied by the unpaired electron (x), and was found to be parallel to {100} directions in the crystal. In NaI the largest 77Se hyperfine interaction in Se2− and SSe− was txx, but in KI tzz was the largest. This is thought to be due to the L·I/r3 term in the hyperfine Hamiltonian, since the contribution of this term to tzz is proportional to gzz−ge.
Vibronic Spectra of Transition-Metal Complexes I. Polarized Emission and Absorption Spectra of NaMg[Cr(C2O4)3]·9H2O
Authors: Mortensen O. Sonnich
Published: January 2005

Polarized emission and absorption spectra of NaMg[Cr(C2O4)3]·9H2O have been obtained at temperatures between 4.5° and 300°K in the frequency range 13 000–45 000 cm−1. Some doublet and all quartet states belonging to the electronic (3d)3 configuration have been located and several vibronic states identified. The intensities of the Laporte-forbidden transitions have been analyzed in terms of electronic and vibronic contributions, and it is shown (i) that both static and dynamic effects are important, (ii) that several vibrational modes are effective, and further, (iii) that even very low-frequency vibrations (phonons) are important. Fine structure has been resolved in the two no-phonon lines corresponding to the electronic transition 4A2→2E, and is assigned to exchange interactions between separate Cr3+ ions.
Comments on the Equation of State of the Square-Well Fluid
Authors: Young David A. , Rice Stuart A.
Published: January 2005

The simple and modified forms of the Yvon—Born—Green equation are solved for a fluid of rigid spheres with attractive square wells. The equation of state is obtained over a range of temperatures and densities. Special attention is paid to the gas—liquid and fluid—solid phase transitions predicted by the YBG equation. At the supercritical temperature kT/ε=3.33 we find nearly exact agreement with Monte Carlo pressures up to a reduced density ρσ3=0.6. At ρσ3=0.75 the disagreement with the best theoretical isotherm reaches 5%. At the critical point we find a reduced pressure (p/ρkt)c=0.50±0.02, which agrees closely with the analytic value of 0.5. In the critical region the isothermal compressibility shows strong maxima and the range of the pair correlations becomes extremely long. The YBG freezing curve shows the same qualitative features as does the Monte Carlo freezing curve.
Calculation of Infrared Intensities by the CNDO Method
Authors: Segal Gerald A. , Klein Michael L.
Published: January 2005

The CNDO method, an approximate self-consistent molecular-orbital theory, has been applied to the calculation of dipole-moment derivatives Mj=(∂μ/∂Sj), where μ is the molecular dipole moment and Sj an appropriate symmetry coordinate. The theory is reasonably successful in calculating both the magnitudes and the signs of Mj for molecules composed of first-row elements and/or hydrogen. The calculations can be understood on the basis of familiar ideas about the changes in atomic hydridization on the bending or stretching of bonds.
Atom—Molecule Kinetics Using ESR Detection. III. Results for O+D2→OD+D and Theoretical Comparison with O+H2→OH+H
Authors: Westenberg A. A. , de Haas N.
Published: January 2005

The technique described previously has been used to measure the rate constant k2 for the reaction O+D2→OD+D over the temperature range 416°—968°K. The data are strictly Arrhenius linear over this range and obey (cm3mole−1•sec−1) k2=2.0×1013 exp(−11 000/RT). A new value of k1 for O+H2→OH+H at 357°K is also reported, which gives a distinct curvature to the low-temperature end of the Arrhenius plot of the k1 data reported earlier. In the range 416°—928°K, where both k1 and k2 are linear, interpretation is made in terms of absolute rate theory without tunneling. A potential-energy surface for a linear transition complex was constructed by the semiempirical Sato method. The average value of the classical potential energy of activation calculated by independently fitting both sets of data is Ec=11 680±120 cal/mole. The theoretical ratio k1/k2 closely follows the experimental ratio in temperature dependence but is about 30% low in magnitude. The theoretical absolute values of the individual pre-exponential factors are in fair agreement with experiment, although also low and not as satisfactory as was found in the D+H2 and H+D2 cases treated previously. Some measurements comparing the decay rates of O(3P2) and O(3P1) in reaction with H2 are also given, which show that the equilibration rate between J=2 and J=1 states is probably much faster than any difference in chemical reaction rates.
Mössbauer Spectrum of Fe2+ in a Square-Planar Environment
Authors: Clark Michael G. , Bancroft G. Michael , Stone Anthony J.
Published: January 2005

The Mössbauer spectrum of high-spin Fe2+, square planar coordinated by oxygens in BaFeSi4O10, has been studied in the temperature range 80°—650°K. The spectrum, a quadrupole doublet, was analyzed by computer fitting, and the results statistically tested using the concept of internal and external consistency. Quadrupole splitting and center shift data are reported for the whole range 80°—650°K, and the widths and relative intensities of the lines have been measured at 80° and 295°K. The quadrupole splitting has been successfully correlated with the magnetic susceptibility and electronic spectrum of Fe2+ in BaFeSi4O10. The lattice contribution is found to be slightly larger in magnitude than the valence contribution, and of opposite sign. By studying both randomized and oriented samples the sign of the quadrupole splitting has been determined experimentally, and the anisotropy of the recoil-free fraction measured. The temperature variation of the center shift has been analyzed in terms of the second-order Doppler shift, and information on the vibrational motion of the iron atom obtained. The theoretical basis of the method used for analyzing the second-order Doppler-shift data is briefly discussed.

A correlation between center shift values and coordination number for minerals containing high-spin ferrous iron is noted; and interesting observations concerning the linewidths, and the effects of heat treatment on the Mössbauer spectrum of gillespite, are reported.
Nuclear Magnetic Resonance Study of Molecular Motions in Hexamethylbenzene
Authors: Allen P. S. , Cowking A.
Published: January 2005

An investigation has been made of the molecular motions occurring in solid hexamethylbenzene by measuring the proton spin—lattice relaxation time and second moment over the temperature range from helium temperatures to 450°K. The reorientation of the methyl groups is found to persist down to 2°K, presumably due to a tunneling mechanism; while the rotation of the whole molecule about its sixfold axis proceeds at a rate greater than a few kilocycles per second above 150°K. No other type of motion seems to occur at such rates, or greater, in the solid. The temperature dependence of T1 is used to estimate the activation energies and motional rates for the respective motions in each of the three solid phases.
Semiclassical Phase Shifts for Low-Energy ``Orbiting'' Collisions
Authors: Herm Ronald R.
Published: January 2005

A semiclassical expression for the phase shift in the literature which is applicable even when a maximum exists in the effective potential is re-expressed in terms of the simple JWKB phase integrals. This expression is employed to calculate phase shifts from tables of reduced functions for a Lennard-Jones (12–6) potential. These semiclassical calculations are compared with published exact values; excellent qualitative and good quantitative agreement is obtained. Finally, the qualitative nature of the quantal corrections to the classical total and differential cross sections and the collision lifetime is discussed.
New Measurements of the Infrared and the Raman Spectrum of S2Cl2
Authors: Bradley Eugene B. , Mathur Maya S. , Frenzel Charles A.
Published: January 2005

The Raman spectrum of S2Cl2 has been excited with a 6-mW He–Ne laser, 6328 Å, and new depolarization ratios of the Raman bands have been obtained. The Raman band at 449 cm−1 previously reported by earlier workers is shown to be two bands corresponding to two fundamentals, one of Type A and another Type of B, at 446 cm−1 and 434 cm−1, respectively. The Raman band at 102 cm−1 corresponding to the torsional mode is found to be polarized in disagreement with earlier investigations; the torsional mode is far-infrared active at 106 cm−1. Three infrared-active fundamentals and six overtones were observed in the 3000–400 cm−1 region. One of these overtones at 1340 cm−1 has not been reported previously. One Raman overtone band and one Raman combination band have been observed at 858 cm−1 and 647 cm−1, respectively. The Raman and infrared data have been correlated with the right-angle configuration of C2 symmetry, and thermodynamic properties have been calculated for the liquid state using the harmonic-oscillator approximation.
Dynamic Mechanical Properties of Chlorinated Biphenyls and Polystyrene—Chlorinated Biphenyl Solutions at 40 MHz
Authors: Moore R. S. , McSkimin H. J. , Gieniewski C. , Andreatch P.
Published: January 2005

Measurements of dynamic shear impedance at 40 MHz and 25°C were carried out on solutions of monodisperse polystyrenes of molecular weight 2.67×105 and 2.39×105 in chlorinated biphenyl solvents (Aroclors). Measurements were also obtained on solutions of monodisperse polystyrenes of molecular weight 2.03×103 and 1.8×106 in di-n-butyl phthalate (DBP). In addition, measurements were obtained on one binary mixture of Aroclors and on five pure Aroclor solvents. These covered a range of 106 in steady-flow viscosity. The dynamic measurements were made by an ultrasonic reflectance technique employing pulse super-position or by a phase-amplitude balancing method. Results for the polystyrene—Aroclor system indicate that the effect of a solvent slightly better thermodynamically than DBP is observed as an increase in the in-phase modulus, whereas little effect is observed in the magnitude of the polymer contribution to the out-of-phase modulus (G″—ωηs), where ω is the angular frequency, ηs is the solvent viscosity, and G″ is the modulus. Measurements on polystyrene dissolved in an Aroclor solvent for which ηs is about 3 P indicate a reduced dynamic viscosity lower by a factor of 2.5 than that obtained at 73 kHz by other workers. Results for the low-molecular-weight polymer (2.3×103) indicate a behavior more nearly Newtonian than that predicted by the Zimm theory, while results for the high-molecular-weight polymer (1.8×106) conform closely to it. Measurements for the Aroclors show that viscoelastic behavior is already significant for an Aroclor with a steady-flow viscosity of 3 P. Logarithmic plots of reduced values of G′ and G″ cross at a reduced frequency of about 109.90 and both G″/ρ and η″/η exhibit a maximum at a reduced frequency of about 1010 Hz. The series is analyzed in terms of several theories of viscoelastic behavior.
Optical Absorption Spectrum and Optical Zeeman Effect in CaWO4:Yb3+
Authors: Jones G. R.
Published: January 2005

The absorption spectrum of 0.01%—0.05% ytterbium-doped calcium tungstate is reported, observed at liquid-helium temperature. Some of the samples contained sodium for charge compensation. The effect of Na charge compensation for Yb was found to be similar to previous results observed for Na-compensated Ce in the same host. The spectrum was found to contain extensive complex structure that may be associated with the known lattice modes. The crystal-field parameters have been calculated to fit the main lines of the spectrum, and the g values that are known. The calculation was made both with and without mixture of states of unequal J. Measurements of the Zeeman effect allow unambiguous identification of the symmetry of the lowest F522 level. In terms of the free-ion JM states this level consists of a combination of M=±52 and ±32 functions. The g values for this state are g‖ = 1.2±0.1 and g⊥ = 1.5±0.1 observed at 31 kOe.
Recombination in Columns
Authors: Wilhelm H. E.
Published: January 2005

Gaseous matter is considered, in which an initially inhomogeneous ionization in columns is produced by charged particles. The simultaneous processes of ionization carrier diffusion from, and recombination in, the columns are calculated for a plasma model considering the effects of different electron and ion mobility in the nonisothermal collective diffusion approximation. Analytical solutions of the space and time dependence of the electron and ion density fields and the electric diffusion field are given, as well as the temporal development of the effective column radius, and the critical time τH for the ionization to become homogeneous. Based on the dynamics of the individual ionization columns, a macroscopic recombination theory is developed resulting in a quasilinear recombinative plasma decay equation for times 0≤t<τH. The effective columnar recombination coefficient is shown to be considerably larger than the atomic recombination coefficient, αN>α for t<τH, and explicitly time dependent due to the internal dynamics of the system, αN→α for t→τH.
Photochemistry of N2O Essential to a Simplified Vacuum-Ultraviolet Actinometer
Authors: Greiner N. R.
Published: January 2005

The net number of molecules generated per quantum absorbed (ΦΔn) in the photodecomposition of N2O with 1849-Å light was shown to be 1.00±0.05 in the range 4 to 214 torr N2O at room temperature. Direct measurement of ΦNO at initial pressures of from 5 to 30 torr N2O, and the constancy of ΦΔn over a large N2O pressure range, indicate that ΦNO probably does not change with N2O pressure under the above conditions. In most other respects, our results agree with those of other workers. It is shown that ΦΔn should be 1.00±0.05 in the range 1380–2100 Å, and that ΦΔn should be ∼0.8 in the range 1200–1380 Å.