bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR Study of Mn2+ in α- and β-Mg2P2O7
Authors: Calvo C. , Leung J. S. , Datars W. R.
Published: January 2005

The electron spin resonance of magnesium pyrophosphate (Mg2P2O7) doped with 0.3% manganese pyrophosphate has been studied at room temperature and in the temperature range of 55° to 94°C using a microwave frequency of 35 Gc/sec. The parameters of the spin Hamiltonian and the orientation of the principal axes of the Mn2+ ion were determined in the α phase at room temperature and in the β phase for the temperature range of 64° to 94°C. The spin-Hamiltonian parameters for Mn2+, assumed to occupy cation sites, are reported for the unique site of the β phase and the two unique sites of the α phase. The principal axes of the spin Hamiltonian of Mn2+ in the α phase were displaced by angles as large as 60° from those in the β phase. The space group of the β phase was determined to be C2/m and that of the α phase confirmed to be B21/c. The phase transformation was found to be reversible and involve the coexistence of both phases from 59° to 63°C.
Theory of the Helix—Coil Transition in DNA Considered as a Periodic Copolymer
Authors: Strässler S.
Published: January 2005

One of the major difficulties in calculating transition curves for the ``melting'' of DNA is to take into account the fact that all of the base pairs do not have the same stability. Two kinds of base pairs of differing stability corresponding to adenine—thymine and guanine—cytosine are recognized by the model used in this paper. For a periodic arrangement of the two base pairs we have reduced the problem of calculating the melting curve to find the largest real eigenvalue of a matrix. Some transition curves are computed for a model with nearest-neighbor correlation only.
Vibrational Relaxation in Pure SO2 and SO2/Ar Mixtures
Authors: Shields F. Douglas
Published: January 2005

Sound absorption and velocity measurements have been made in pure SO2 and mixtures of 25% and 50% Ar with SO2 at room temperature, 400°, and 500°K. The results confirm earlier reports of a multiple relaxation process. The data have been fit with both series and parallel relaxation curves and the temperature dependence of the individual relaxation times determined. The difficulty in distinguishing between the two processes is discussed.
Dielectric Properties of Hydrogen Halides. III. High-Frequency Dispersion in Solid Phases of HI and HBr
Authors: Groenewegen P. P. M. , Cole R. H.
Published: January 2005

Dielectric constant and loss measurements have been made at frequencies from 5 to 225 MHz. These are in the range to characterize the relaxation in the intermediate solid phase of HBr from the 89°K λ transition to 98° K and, together with earlier data, the relaxation in HI from the 70°K transition to 92°K. The complex dielectric constant is described in both cases by a skewed arc function rather than the symmetric circular arc functions found for the low-temperature phases. The corresponding loss of long-time dipole correlations suggests a more liquidlike behavior. It is further suggested that deviations of the relaxation rates from temperature dependence of Arrhenius form may be explainable in terms of cooperative interaction effects in a disordered phase.
Adsorption of Flexible Macromolecules. III. Generalized Treatment of the Isolated Macromolecule; The Effect of Self-Exclusion
Authors: Silberberg A.
Published: January 2005

A generalized treatment of adsorption at an interface of an isolated flexible macromolecule from solution is presented. Adsorption is assumed to involve the arrangement of the segments of the chain into conformations in which loops of segments and trains of segments attached to the surface alternate each other. Adsorption will occur only if the free-energy change ΔFs per segment in going from loop to train is less than a critical value. For a very long chain (no end effects) the distribution functions of loop and train sizes do not depend on the length of the chain. The arrangment possibilities of the loops and trains are represented by functions of the type ω(i) = γi−aui which have been used to allow for nonintersection effects (volume exclusion effects) in random walks. If in the above, the exponent a characterizes loops and the exponent ā trains, it is conjectured that the proper choice of (a, ā) is (43, —⅓) rather than (32, 0). With this choice, self-exclusion within the loops and trains is allowed for. It is shown that a reduction in the a priori probability of leaving the surface and returning to it [small (γγ̄)] favors large loops. The ratio (ū/u) is shown to equal 0.4 independent of lattice type.
ESR Studies of Naphthoquinones and Related Compounds. Hyperfine Interaction by the Methoxyl Group as a Conformational Probe
Authors: Rabold Gary Paul , Ogata Ronald T. , Okamura M. , Piette L. H. , Moore R. E. , Scheuer P. J.
Published: January 2005

ESR spectra were run on a large number of methoxy-substituted para-semiquinones. With the help of MO calculations it was deduced that methoxyl hyperfine interaction in these systems is, in part, a function of the spin density on the ether oxygen. By the use of model compounds it was further deduced that only one conformational isomer is effective in giving rise to splitting. A semiempirical value for |QOCH3| was calculated to be 5.6 G.
Infrared Spectrum of HN3 and DN3: Assignment of the Coriolis-Coupled Bending Vibrations
Authors: Levine D. M. , Dows David A.
Published: January 2005

The complex infrared vibration—rotation spectra of hydrazoic acid and deuterohydrazoic acid from 400–1000 cm−1 have been studied. The prominent Q branches have been assigned to three Coriolis-coupled vibrational transitions. From an analysis of the observed frequencies, band origins and Coriolis constants have been determined. HN3: v3=1263.7, v5=534.2, v6=607.0, ζ36z=−0.31, ζ56z=−0.93±0.02; DN3: v4=953.8, v5=492.2, v6=588.4, ζ46z=−0.41, ζ56z=−0.82±0.02.

Coriolis coupling between v5(a′) and v6(a″), combined with the inherently small intensity of v6, causes v6 as well as v5 to exhibit predominantly parallel character. The anomalous intensity distribution has been the cause of previous difficulty in assignment.
Infrared and Raman Spectra of Vinylene Carbonate
Authors: Dorris Kenneth L. , Boggs James E. , Danti Alfred , Altpeter Lawrence L.
Published: January 2005

The infrared and Raman spectra of vinylene carbonate have been observed from 50 to 4000 cm−1 and most of the fundamental modes of vibration have been assigned. The B2 ring-puckering vibration is at 258 cm−1 in the liquid, in good agreement with the results of microwave intensity measurements. A short C–O bond length, on the order of 1.15–1.17 Å, is indicated by the high frequency of the carbonyl stretching frequency.
Low-Energy, Large-Angle Electron-Impact Spectrum of Ethylene
Authors: Doering John P.
Published: January 2005

The electron-impact spectrum of ethylene has been measured at primary energies of 35, 50, and 70 eV and a fixed scattering angle of 90°. The most intense inelastic peak was found to be at 8 eV. This peak corresponds to a number of unresolved allowed transitions which are observed in the vacuum-ultraviolet absorption spectrum. A peak was observed at 4.6 eV which was assigned to a forbidden singlet—triplet transition. The 6.5-eV ``ultraviolet mystery band'' transition was not observed. Neither was any peak observed in the spectrum which could be assigned to a large inelastic process at the ionization limit.
Activated Adsorption of Hydrogens on Aromatic—Alkali-Metal Charge-Transfer Complexes
Authors: Inokuchi Hiroo , Wakayama Nobuyuki , Kondow Tamotsu , Mori Yoshihiro
Published: January 2005

The ortho—parahydrogen-conversion reaction (p-H2⇌o-H2) and the hydrogen—deuterium exchange reaction (H2+D2⇌2 HD) were used to investigate the activated adsorption of hydrogen on aromatic—alkali-metal charge-transfer complexes. When deuterium gas was introduced onto these complexes, it was found that hydrogen exchange takes place between deuterium and the complexes (denoted as H2⇌D2). The kinetics of the parahydrogen conversion and of the H2—D2 exchange were studied as a function of the temperature and it was found that the rate of reactions was first order at a constant pressure. On the basis of the effect of the temperature on the rate constant, an apparent activation energy E for p-H2⇌o-H2 was 4.4 kcal/mole in the presence of phthalonitrile—Na (I), 3.7 kcal/mole with tetracyanopyrene—Cs (II), 10.0 kcal/mole with violanthrene B–Cs (III) and 0.6 kcal/mole with graphite—Cs (IV). Further, E for H2+D2⇌2 HD was 6.6 kcal/mole in the presence of (I) and ∼0.6 kcal/mole with (IV). These reaction suggests that the strong activated adsorption of hydrogen on the complexes takes place with the excess charge transferred from alkali metal to the organic molecule. Further, it was found that the hydrogen exchange reaction between gaseous hydrogen and phthalonitrile takes place reversibly.
Symmetry Properties of One- and Two-Electron Correlation Functions in the Many-Electron Theory of Atoms and Molecules
Authors: Silverstone Harris J. , Sinanoğlu Oktay
Published: January 2005

The symmetry properties of the many-electron wavefunctions containing unlinked clusters are shown to follow directly from those of the wavefunctions with one- and two-electron correlations occurring one at a time for both closed- and nonclosed-shell states. The separate calculation and symmetry properties of distinct pair functions in general nonclosed- and closed-shell states are discussed. The symmetry considerations carry over to the localized-orbital+localized-pair-function descriptions.
Chemisorption and Oxidation: Oxygen on Tungsten
Authors: McCarroll Bruce
Published: January 2005

Oxygen chemisorption and the extent of oxidation on a tungsten ribbon at room temperature were studied by flash desorption using line-of-sight detection with a time-of-flight mass spectrometer. The only chemical species in the adlayer are oxygen atoms and the monotungstic oxides: WO, WO2, and WO3. These oxides are desorbed with an energy of ∼100 kcal. In agreement with earlier predictions, oxygen desorbs as atoms. Neither molecular oxygen nor polytungstic oxides were ever observed from a ribbon flashed after a room-temperature exposure to oxygen. However, flowing oxygen on tungsten at surface temperatures > 1400°K does produce the polytungstic oxides. An order-of-magnitude estimate of the adlayer composition at room temperature suggests that at saturation there is approximately one monolayer of oxygen atoms in a random configuration with a few tenths of a per cent each of the monotungstic oxides. Consequently, oxidation is not a significant surface process on clean tungsten at room temperature.
Study of BeH3−, BH3, CH3+, NH3++, and OH33+ by One-Center-Expansion, Self-Consistent-Field Method
Authors: Joshi Bhairav D.
Published: January 2005

One-center-expansion, self-consistent-field calculations are carried out for BeH3−, BH3, CH3+, NH3++, and OH33+ systems. Using a limited basis set, all of these molecules are found to be planar (θZAH=90°), except the OH33+ system which is found to be unstable. The extended-basis-set calculations are carried out only for BeH3−, BH3, CH3+, and NH3++. These calculations give the internuclear distances to be 2.500, 2.191, 2.032 and 2.074 bohrs, respectively, the total energies −16.144047, −26.235841, −39.117795, and −54.980821 hartrees, respectively, and the first ionization potential (—ε1e′) 0.1402, 0.4802, 0.9293, and 1.4329 hartrees, respectively. Estimated values of the Hartree—Fock energy and the total nonrelativistic energy are also given for these four molecules.
Electron Spin Resonance of Dy3+ in LaCl3
Authors: Brower K. L. , Stapleton H. J.
Published: January 2005

We have examined the electron spin resonance spectrum of trivalent dysprosium in a single crystal of anhydrous lanthanum trichloride and have identified weak forbidden resonances as originating from the ground doublet in sites of distorted and essentially undistorted crystal symmetry. Also present in the spectrum is an allowed transition between the energy levels of the first excited doublet. The ESR spectrum due to the ground doublet in an undistorted site can be described by an axially symmetric spin Hamiltonian with S=½, g∥=10.43±0.05 and g⊥<1. The ESR line from the excited-state transition fits an axially symmetric spin Hamiltonian with S=32 involving the operators HiSi, Si2, and HiSi3; the latter terms being necessary to account for the effects of another doublet 0.135±0.01 cm−1 away. This measurement of the zero-field splitting is in good agreement with the optical value of 0.15 cm−1. The remaining parameters of the S=32 spin Hamiltonian are also in reasonable agreement with values computed from crystal-field theory.
Variational Procedure for Open-Shell LCAO Multideterminant Wavefunctions. An Approach to the Excited-State Problem
Authors: Rossi M.
Published: January 2005

A procedure recently suggested for solving the LCAO problem is applied to open-shell LCAO wavefunctions built up by adding many determinants having the same spatial part which, commonly, are used to approximate the wavefunction of excited states.

The procedure is extended to the case when an orthogonality condition must be explicitly imposed with given wavefunctions representing lower-energy states.
Diatomic-Ion—Molecule Reactions: N2+–N2, CO+–CO, and O2+–O2
Authors: Leventhal J. J. , Friedman L.
Published: January 2005

New channels of reaction have been found in the N2+–N2 and CO+–CO ion—molecule systems. These processes which account for a major fraction of the total ion—molecule collision cross section yield, respectively, N+ and C+ ions. A study of the energetics of the respective processes leads to the conclusion that stable neutral N3 and CO2 are also formed. A value of approximately 6 eV is obtained for the energy of dissociation of N3 radicals into N and N2. Minor reaction products N3+ and C2O+ observed in earlier studies of the N2+–N2 and CO+–CO systems were also observed in this work. In the O2+–O2 system only O3+ ions were detected and in relatively minor yields. Production of O3+ rather than O+ is energetically favored. The relatively small yield of O3+ is shown to be a result of the energetics of the system which tends to cycle O3+ back to O2+ and O atoms which are not detected in the mass-spectrometer analysis of reaction products. In all three systems over-all reaction cross sections were found to be in good agreement with theoretical values of ion—molecule collision cross sections when sufficient energy is available and all channels of reaction are taken into consideration.
Measurements of Electron Impact Excitation Cross Sections of Laser States of Argon(II)
Authors: Hammer J. M. , Wen C. P.
Published: January 2005

Cross sections for the excitation of the upper laser levels 4p2D5/2, 2D3/2, 2P3/2, and 2S1/2 of Ar (II) by electron impact with ground-state neutral atoms have been found by measuring the incoherent light produced by a triode-type structure filled with argon to pressures near 0.1 torr. Peak values in the vicinity of 5×10−19 cm2 are found. By operating the same structure in an argon-ion laser cavity, an increase in coherent output is measured. The amount of the increase in output may be used in conjunction with the measured upper-state cross section to estimate the cross section for electron excitation of the lower laser levels.
Electron Spin Resonance and Optical Absorption Studies of Cr3+ in a Phosphate Glass
Authors: Landry R. J. , Fournier J. T. , Young C. G.
Published: January 2005

Optical absorption and electron spin resonance (ESR) spectra of a chromium-doped phosphate glass have been studied as a function of Cr2O3 concentration. While the optical spectrum appears to be independent of chromium-ion density, the ESR spectrum exhibits a pronounced concentration dependence. The spectra have been attributed to a combination of isolated, octahedrally coordinated Cr3+ and antiferromagnetically coupled pairs of Cr3+ ions which are individually sixfold coordinated. The measured value of the crystal-field parameter Δ is 14 500 cm−1. The ESR data are analyzed within the framework of the spin-Hamiltonian formalism. In the case of the isolated Cr3+ it is estimated that the axial field parameter | D | lies in the range 0.15 to 0.5 cm−1. The assumption of a relatively strong isotropic exchange interaction is adequate to describe the gross features of the Cr3+ pair spectrum. Speculative models for the glass structure in the neighborhood of an isolated Cr3+ ion and a Cr3+ pair are presented.
First-Order Ferroelectric Transition in (NH4)2SO4
Authors: O'Reilly Donald E. , Tsang Tung
Published: January 2005

A modified molecular-field approximation is presented in which a dependence of the interaction parameters on the number of misoriented ion pairs is explicitly included. The usual second-order phase transition becomes first order for a sufficiently strong dependence of the interaction parameters on the number of misoriented pairs. Values of the parameters for a simple lattice necessary to account for the transition in (NH4)2SO4 are given. A qualitative explanation of the dependence of the crystal volume on temperature is proposed based on the hydrogen-bond structure of (NH4)2SO4.
Thermodynamic and Conformational Properties of Polystyrene. II. Intrinsic Viscosity Studies on Dilute Solutions of Linear Polystyrenes
Authors: Berry G. C.
Published: January 2005

The results of an extensive study of the intrinsic viscosity [η] of a series of linear, homogeneous (anionically prepared) polystyrenes (1.9<10−4M<440) over a wide temperature interval (10°<T<110°C) in decalin and toluene are described. The data are discussed in relation to the interaction parameter z=B0(〈s2〉0/M)−3/2(1−Θ/T)M1/2 in which the constants B0, Θ, and 〈s2〉0/M have been determined from thermodynamic studies reported in Part I of this series. It is found that [η]/[η]0 is not a single-valued function of z except for M>∼106. Above this molecular weight the dependence of [η]/[η]0 on z is satisfactorily predicted by recent calculations of Fixman; [η]/[η]0 is not linear in z contrary to other recent suggestions. The failure of the data on lower molecular weight polymers to be a single-valued function of z is discussed in terms of partial draining effects.
fd and f13d Configurations in a Crystal Field, and the Spectrum of Yb++ in Cubic Crystals
Authors: Piper T. S. , Brown J. P. , McClure D. S.
Published: January 2005

The energy levels of the configurations fd and f13d in cubic crystal fields have been calculated as a function of the f- and d-electron crystal-field parameters. The results are used to explain the spectrum of Yb++ in SrCl2. Both the calculated energies and calculated intensities agree well with experiment.
Radiationless Transitions in Cyanine Dyes
Authors: Buettner A. V.
Published: January 2005

The quantum yields of fluorescence and the maximum quantum yield of triplet produced have been measured for three cyanine dyes in thin films of polyvinyl alcohol. The fraction of excited dye molecules which neither fluoresce nor undergo intersystem crossing to the triplet state and which, therefore, must undergo a nonradiative transition from the excited singlet state to the ground state is equal to or greater than 0.86±0.05 for 1,1′-diethyl−2,2′-cyanine iodide, 0.82±0.04 for 1,1′-diethyl−6-bromo−2,2′-cyanine iodide, and 0.64±0.06 for 1,1′-diethyl−6-iodo−2,2′-cyanine iodide.
Mass-Spectrometric Studies of the Synthesis, Energetics, and Cryogenic Stability of the Lower Boron Hydrides
Authors: Wilson J. H. , McGee H. A.
Published: January 2005

Ionization-efficiency measurements on species produced in the pyrolysis of B2H6 have led to A (B+), A (BH+), A (BH2+), A (BH3+), and A (B2H5+) from B2H6 and to A (B+), A (BH+), A (BH2+), and I (BH3) from BH3. These experimental results have permitted a rather complete development of the energetics of the BH3; B2H6 system and its related radicals and ions, including the important symmetric dissociation energy, D (BH3–BH3), which was found to be 2.56 eV. BH2 was not observed in these experiments and thermodynamic and kinetic arguments, using the results of this investigation, predict that BH2 should be of little significance in the pyrolysis mechanism. Using a cryogenically cooled mass-spectrometric system the existence of BH3 and BH2F as stable cryochemicals was explored at temperatures down to 55°K with negative results.
Proton Resonance Spectra of Some Gas Hydrates
Authors: Brownstein S. , Davidson D. W. , Fiat D.
Published: January 2005

Proton resonance spectra have been obtained for a variety of clathrate hydrates as a function of temperature from near the decomposition point to about −70°C. It is possible to calculate the Arrhenius activation energy (∼8 kcal mole−1) for motional narrowing of the linewidths of the host molecules and this is attributed to the combined effects of rotation and diffusion in the solid. By selective deuteration linewidths are found for proton-containing guest molecules. The guest molecules undergo rapid rotation in the solid.
Vacuum-Ultraviolet Absorption of Shock-Heated Vibrationally Excited Nitrogen
Authors: Appleton J. P. , Steinberg M.
Published: January 2005

Absorption coefficients of shock-heated nitrogen have been measured over a temperature range from 3500° to 10 000°K at four wavelengths: 1086, 1176, 1247, and 1334 Å. The experiments were performed behind the reflected shock about 1 cm from the end wall of a 3-in-diam shock tube which was equipped with lithium fluoride windows. Light from a pulsed hydrogen discharge lamp passed across the shock tube at the window station and entered the entrance slit of a 0.5-m Seya—Namioka monochromator. The intensity at the exit slit was recorded using an oscilloscope and a photomultiplier which monitored the fluorescence emitted from a thin coating of sodium salycilate on a quartz screen which was placed immediately behind the exit slit. Absorption of the transmitted light was measured behind the reflected shock at times after vibrational equilibration but prior to significant dissociation.

The temperature dependence of the absorption coefficient obtained at each wavelength indicated that the absorption was due to photoexcitation of molecules from within one or two adjacent vibrational levels of the ground electronic state X 1Σg+ [to the b′ 1Σu+(12.849 eV)] the b 1πu(12.575 eV), and probably to other states of comparable energy. Upper limits for the values of the electronic f numbers for the b′←X and b←X transitions were deduced from the experimental data using previously calculated values of the absorption coefficients per unit f number for these bands. Approximate measurements of vibrational relaxation times at 1334 Å (v″≃13) have also been obtained which agree fairly well with the lower temperature measurements of previous investigations.
Determination of Two- and Three-Body Relaxation Times from Collision-Induced Absorption
Authors: Birnbaum George , Levine Howard B. , McQuarrie Donald A.
Published: January 2005

A theory is developed for analyzing microwave collision-induced absorption in a gas containing quadrupolar nondipolar molecules in terms of two- and three-body interactions. Relaxation times for two- and three-body collisions are obtained.
Extended Hartree—Fock Ground-State Wavefunctions for the Lithium Molecule
Authors: Das G.
Published: January 2005

A configuration-mixing method is described for single-bonded diatomic molecules, in which both the orbitals from which the configurations are constructed, as well as the mixing coefficients, are optimized by way of solving SCF-type equations. The method properly describes molecular formation, which is not in general possible when using the Hartree—Fock molecular-orbital method. Numerical results are presented for the Li2 molecule. The calculated potential curve is closely parallel to an empirical curve obtained by using spectroscopic constants. The difference between the two curves may be interpreted as the correlation energy of the core electrons, and is essentially constant over the complete range of internuclear distances of chemical interest.
Evaporation—Condensation Coefficient for Small Droplets
Authors: Okuyama Masataka , Zung Joseph T.
Published: January 2005

The evaporation—condensation coefficient for very small droplets is derived in the form α(a) =δ·φ(a), where δ is the free-angle ratio and φ(a) is the size coefficient which is expressed in terms of the droplet radius a, the absolute temperature, and other characteristic variables of the liquid phase and the gas—liquid interface. With the inclusion of α(a) into the rate equations of Fuchs and of Monchick and Reiss, the rate of evaporation per unit area increases with decreasing droplet radius, reaches a maximum at droplet radii ranging between 1 and 0.01 μ, then decreases to zero as the radius approaches zero. Numerical results were obtained for H2O, He, and Hg at their respective freezing and boiling points.
Dissociative Charge Exchange of Rare-Gas Ions with C2F6 and C3F8
Authors: Smith Dave , Kevan Larry
Published: January 2005

Dissociative charge exchange of rare-gas ions with C2F6 and C3F8 has been studied. The data was obtained with a single-stage Nuclide mass spectrometer by operating the ion source in the Čermák—Herman mode. A charge-transfer mass spectrum was obtained for C2F6 and C3F8 with each rare-gas ion except Xe. The relative ionic abundances were interpreted as portraying the dissociation of C2F6+ and C3F8+ as a function of their excitation energy. The normalized abundance of CF8+ as a funetion of excitation energy shows two maxima which indicates that two processes contribute to CF3+ formation from C2F6 and C3F8.
Performance of a New Photoelectric Detection Method for High-Resolution Optical Spectroscopy. I. Investigation of Basic Characteristics
Authors: Pao Yoh-Han , Griffiths James E.
Published: January 2005

Recently, Pao, Zitter, and Griffiths reported on a new method of detecting light signals of low intensity. The results of a more detailed investigation of the nature and characteristics of this method are presented in this paper. In this new method, the conventional slowly varying signal is discarded and the mean of the square of the fluctuations is detected instead. It is shown that in principle the incident light can be detected equally well this way. Furthermore this method is effective in discriminating against dark-current noise and in practice seems to perform better than dc and phase-sensitive detecting systems at low light intensities.
Internal Energy of Reaction Products by Velocity Analysis. III. Center-of-Mass Angular Distribution and Product Excitation Function for K+Br2
Authors: Warnock T. T. , Bernstein R. B. , Grosser A. E.
Published: January 2005

A computer analysis of the product (KBr) velocity distribution experiments previously reported for the crossed molecular beam reaction K+Br2 is presented. The shape of the angular distribution of KBr in the center-of-mass (c.m.) system and the product internal energy (excitation) distribution function are evaluated, subject to the assumption of no coupling between the two distributions. In agreement with the conclusions of Herschbach, Datz, and their co-workers, the differential reaction cross section in the c.m. system is strongly forward peaked, characteristic of a ``stripping'' reaction. The maximum in the internal excitation function occurs near 100% of the total available energy. The results are in fair accord with the predictions of Karplus, Polanyi, and their co-workers, based on Monte Carlo trajectory analyses employing semiempirical potential surfaces.
Rates of Addition of Methyl Radicals to Olefins in the Gas Phase
Authors: Cvetanović R. J. , Irwin R. S.
Published: January 2005

A technique has been developed and used to measure relative rates of reaction of methyl radicals with a number of olefins in the gas phase at 80°, 130°, and 180°C. The rate constants, activation energies, and pre-exponential factors have been determined.
Theory of Correlated Wavefunctions. IV. A ``Configuration Interaction Plus Perturbation'' Approach
Authors: Steiner Erich
Published: January 2005

The perturbation—variation treatment of electron correlation is generalized to include a many-configuration initial approximation Ψ0 which is a linear combination of all those configurations consistent with a chosen basis set of orbitals. Such a generalization enables all configurations that make a large contribution to the wavefunction to be included in Ψ0, so that the problem of degeneracies and near-degeneracies is removed, and the correction to Ψ0, being essentially small, may then be determined by first-order perturbation theory. The initial approximation may be determined using configuration-interaction methods, which gives upper bounds to a number of states. Excited states may be treated as easily as, and together with, the ground state. It is shown that when Ψ0 is the optimum combination of configurations consistent with a chosen orbital basis, for any state, then it is invariant under a unitary transformation of the orbitals of the basis. This allows a transformation to orbitals which optimize the contribution of the first-order wavefunction.
Intermolecular Forces in the Region of Small Orbital Overlap
Authors: Murrell J. N. , Shaw G.
Published: January 2005

The perturbation method of Yaris for the case where the unperturbed wavefunction is not an eigenfunction of the unperturbed Hamiltonian is developed to give an expression for intermolecular energies in the region of small orbital overlap. The resulting expressions are the same as these obtained earlier using a more traditional aproach, but the derivation does not suffer the lack or rigor in this earlier treatment.
Some Factors Affecting the Phosphorescence/Fluorescence Ratio in Tyrosine Following Excitation to Higher-Lying Excited Levels
Authors: Rau Hermann , Augenstein Leroy
Published: January 2005

With respect to its phosphoresence/fluorescence (P/F) ratio at 77°K, the behavior of tyrosine can be divided into four categories: (a) Above pH 8 there are large increases in P/F which parallel the OH⇌O− equilibrium changes. Since identical changes are observed in both (P/F)225 and (P/F)275 (i.e., excitation to either the 225- or 275-nm band), the effect of the acid—base shift must be only on the lowest excited state. (b) Also, in the range pH 5–8 (P/F)225 = (P/F)275, indicating that essentially all of the intersystem crossing still occurs in the lowest exicted state. (c) Below pH4, however, (P/F)225 increases rapidly until it becomes ∼1.3 (P/F)275: This ``acid effect'' has a pK of about 3.5 whether the acid is formic or HCl. The corresponding increase in phosphorescence yield suggests that either the acidification enhances intersystem crossing in the second excited level at the expense of radiationless transitions which are most pronounced at neutral pH or else protonation changes lead to excited molecules with changed emission probabilities—since the yields, energies, and lifetimes of phosphorescence remain constant in this region, the acidification must not perturb the lowest lying triplet of those molecules which do emit. (d) Throughout the acid and neutral region, increasing the ionic concentration increases (P/F)225 and (P/F)275 equally and causes a decrease in the phosphorescence lifetime but not energy: 0.07M NaCl is sufficient to produce one-half the maximum effect. This ``salt effect'' is apparently on the lowest excited triplet and presumably reflects perturbations depending upon changes in the frozen matrix surrounding the solute molecules. These effects cannot be accounted for on the basis that appreciable crystallization of tyrosine occurs during freezing.
Substituent Effects. VI. Theoretical Interpretation of Additivity Rules of NMR Using McWeeny Group Functions
Authors: Vladimiroff Theodore , Malinowski Edmund R.
Published: January 2005

McWeeny group functions, in conjunction with the popular Ramsey formulation, are used to theoretically account for the additive influence of substituents observed in NMR spectra. In this treatment the group wavefunctions are assumed to perturb one another only to first order. This approach is applied to chemical shifts and coupling constants involving various types of nuclei. In general, the substituent effect is found to be pairwise additive. If the substituent is far removed from the nuclei in question then the pairwise rule reduces to direct additivity. For a local operator, such as the Fermi contact term in spin coupling, the effects of substituents are directly additive even though the substituents are bonded to one of the nuclei in question. If the group wavefunctions act as a large perturbation on one another then the second-order terms cannot be neglected, and the simple direct and pairwise additivity rules fail. Existing data and new data are discussed in terms of the above theoretical treatment.
Solution Properties of Synthetic Polypeptides. IV. Trimethylenediamine-Initiated Poly-γ-Benzyl-L-Glutamate
Authors: Teramoto Akio , Yamashita Tsuneko , Fujita Hiroshi
Published: January 2005

A polypeptide was synthesized by polymerization of N-carboxy-γ-benzyl-L-glutamate anhydride in dioxane containing trimethylenediamine (TMDA) as initiator. When dissolved in a helicogenic solvent, such as dimethylformamide (DMF), this polypeptide molecule is expected to take a gross conformation which may be pictured as two rigid rods linked by a flexible joint, since the TMDA residue is intolerant of intrachain hydrogen bonding. Light scattering, osmotic pressure, viscosity, and sedimentation rate were measured on seven samples of this polypeptide in DMF at 25°C, and the results were compared with the corresponding data on triethylamine (TEA)- or sodium methoxide (SMO)-initiated PBLG, which presumably assumes the form of a straight rod in DMF, as can be argued from various existing evidences. It was found from this comparison that the introduction of one freely bending portion into a rigid-rod macro-molecule hardly affects the dependence on molecular weight (and slightly the absolute magnitude as well) of [η] and s0 characteristic of rigid rods. Thus, for M̄w larger than 105, the values of s0 of TMDA-initiated PBLG samples were only 0.15 (in Svedberg units) higher than those of TEA- or SMO-initiated PBLG samples of equal molecular weight, almost independently of M̄w. Likewise, the [η] values of the former were lower by a constant factor of about 14% than those of the latter when M̄w was above 105. The accuracy of these numerical results, however, should be taken with some reservation, because a possibility that the TMDA-initiated PBLG is a mixture of straight and once-broken rod polypeptides was also suggested.
Far-Infrared Spectra of HCl and HBr in Solid Solutions
Authors: Katz B. , Ron A. , Schnepp O.
Published: January 2005

The far-infrared absorption spectra of HCl, DCl, HBr, and DBr in solid solutions in the hosts Ar, Kr, Xe are described in the wavelength range 33–100 cm−1. One band was observed for each solid solution close to the presumed phonon band of the respective host. The absorption peak frequency was identical for HCl and HBr for all three hosts investigated. The observed spectra are discussed in terms of both a localized mode model and activated phonon bands, the latter affording the more likely interpretation. The principal source of the observed intensity is demonstrated to be the coupling between rotation of the solute molecule in the host lattice and translational motion.
Determination of Centrifugal Distortion Coefficients of Asymmetric-Top Molecules
Authors: Watson James K. G.
Published: January 2005

The rotational Hamiltonian of an asymmetric-top molecule in a given vibrational state, obtained by the usual vibrational perturbation treatment, contains more parameters than can be determined from the observed energy levels. This Hamiltonian is therefore transformed by means of a unitary transformation to a reduced Hamiltonian which is suitable for fitting to observed energies. The unitary transformation can be chosen so that the reduced Hamiltonian has the following properties: (i) It is totally symmetric in the point group D2, regardless of the symmetry of the molecule; (ii) It contains only (n+1) independent terms of total degree n in the components of the total angular momentum, for each even value of n; (iii) Its matrix elements in a symmetric-top basis satisfy the selection rule ΔK=0, ±2. This paper is concerned mainly with the possibility of carrying out this reduction in general. However, the reduced Hamiltonian described above contains one less quartic coefficient than has been used previously, and this particular case is discussed in more detail.
Electron Spin Resonance Absorption Spectra of CO3− and CO33− Molecule—Ions in Irradiated Single-Crystal Calcite
Authors: Serway R. A. , Marshall S. A.
Published: January 2005

Single crystals of x- and γ-irradiated calcite reveal a number of paramagnetic defect centers, two of which have been tentatively identified as the CO3− and CO33− molecule—ions. The ESR absorption spectrum of what is believed to be the CO3− molecule—ion is found to have symmetry about the calcite [111] direction with spin-Hamilton parameters given by g‖=2.0051, g⊥=2.0162, A‖=13.1 Oe, and A⊥=9.4 Oe. The corresponding parameters for what is believed to be the CO33− molecule—ion which also exhibits symmetry about the crystal [111] direction are given by g‖=2.0013, g⊥ =2.0031, A‖=171.22 Oe, and A⊥=111.33 Oe. The parameters of these two spectra are discussed and compared with those reported for the isoelectronic NO3 and NO32− species. Optical measurements reveal two absorption bands, one at 6500 Å and another at 4850 Å. The longer-wavelength band exhibits anisotropy and is found to have temperature-dependent decay characteristics which are similar to those of the CO3− molecule—ion ESR spectrum. An activation energy of 0.12 eV is obtained for this center. Thermal decay data suggest that the shorter-wavelength band is not associated with either of these paramagnetic species.
Problem of ``Vertical'' Correlation in Pi-Electron Systems
Authors: Alexander Millard H.
Published: January 2005

The problem of ``vertical'' correlation is re-examined. Defined in terms of the two-electron probability distribution function, ``vertical'' correlation is separated from the related ``in—out'' correlation effect. A study is made of the planar methyl anion and its isoelectronic analog, the planar ammonia molecule, to assess the importance of sigma antibonding orbitals for the correlation of the 2pz2 pair. These contribute −0.092 eV for planar CH3− and −0.120 eV for planar NH3. The implications for Σ—II separability are discussed.
Study of Phenothiazine— and Chlorpromazine—Iodine Complexes
Authors: Gutmann F. , Keyzer H.
Published: January 2005

In the solid state, phenothiazine (PH) complexes with iodine to yield a resistivity minimum of 350 Ω·cm at 2:3 stoichiometry. The chlorpromazine (CPZ):I2 system behaves likewise, the minimum resistivity is 420 Ω·cm. The ESR signal intensities also peak at this ratio. Conductimetric titrations in acetonitrile solution indicate a stoichiometry between 1:2 and 2:3 for the PH:I2 complex. CPZ·HCl produces a conductivity peak at 1:2, while freshly prepared free base CPZ complexes with I2 in a 1:1 ratio at room temperature. CPZ aged in solution or in the solid state yields a 2:3 complex at room temperature changing to 1:2 at 50°C with I2 in acetonitrile. Infrared spectra of these complexes are reported and discussed. Those of the CPZ:I2 complex resemble that of liquid or supercooled CPZ rather than that of solid CPZ. The CPZ:I2 as well as the CPZ·HCl:I2 complexes show a new band at about 1700 cm−1. Palladous chloride tests of the complexes were negative, indicating the absence of iodide ions. From the similarity of the PH:I2 and CPZ:I2 complexes in their electrical properties and in view of the fact that the stable form for both occurs for the 2:3 ratio it is likely that the main donor activity of CPZ resides in the phenothiazine nucleus and not in the side chain. However, there is evidence of at least three different complex species in the PH:I2 or CPZ:I2 systems. The I2 complexes of both PH and CPZ strongly resemble the high-temperature forms of their donor parents; thus it is not unlikely that self-complexing takes place in PH and in CPZ, especially at elevated temperature.
Localized Orbitals for NH3, C2H4, and C2H2
Authors: Kaldor Uzi
Published: January 2005

Localized orbitals were obtained for NH3, C2H4, and C2H2 by the Lennard-Jones and Pople criterion of minimizing the interorbital and maximizing the intraorbital Coulomb and exchange energy. Orbitals conforming to the chemical-bonding picture (an inner shell, three N–H bonds and a lone pair) were obtained for pyramidal NH3. ``Bent bonds'' were obtained for planar NH3. In the cases of C2H4 and C2H2 there are the usual inner shells and C–H bond orbitals (the latter being bent for twisted ethylene), while the C–C bonds are equivalent ``banana orbitals,'' two for the ethylene double bond and three for the acetylene triple bond. Some cases of nonuniqueness of the localized-orbital description are discussed.
Theoretical Analysis of the Effects of Hydrogenation in Hydrocarbons: Accurate SCF MO Wavefunctions for C2H2, C2H4, and C2H6
Authors: Buenker Robert J. , Peyerimhoff Sigrid D. , Whitten Jerry L.
Published: January 2005

A close relationship between the hydrocarbon molecule series acetylene to ethane and the homonuclear diatomic molecules N2 to F2 is demonstrated by means of accurate SCF calculations for each of these systems and C2. This fact enables one to analyze changes in corresponding orbital energies between members of the hydrocarbon series and C2 concisely in terms of three well-defined effects: changes in CC bond lengths, selective participation of hydrogen AO's in the hydrocarbon MO's, and a nonbonded interaction due to electron withdrawal from hydrogen atoms. This analysis, in turn, makes it possible to explain changes in minimum ionization potential in the hydrocarbon series and the relationship between bond lengths and binding energies between members of both series.
Reactions between Vacancies and Impurities in Magnesium Oxide. I. Cr3+-Ion Impurities
Authors: Glass A. M.
Published: January 2005

Reactions between cation vacancies and Cr3+ impurity ions in single crystals of magnesium oxide are studied using optical techniques to determine the concentrations of the reaction components. Several new features of the Cr3+-ion luminescence spectrum are reported. The spectrum of these impurity ions is very sensitive to local variations of crystal structure. The effect of heat treating MgO crystals, and quenching them to room temperature, on the photoluminescence and cathodoluminescence spectra of the Cr3+ ions is investigated. The variation of intensities of the spectral lines with heat treatment is accounted for by the variation in concentration of impurity-ion—vacancy associates in the lattice. It is found that below 400°C cation vacancies are essentially immobile in MgO, whereas between 400° and 900°C the impurity—vacancy interaction may be accounted for in terms of simple mass-action theory. Above 900°C MgO reacts with the surrounding atmosphere, and the diffusion of defects into the crystal is observed. The experiments considerably aid the interpretation of the spectra, and in several cases the entropy and enthalpy of association of the defects is evaluated.
Polarized Infrared Spectra of Single Crystals of 9,10-Anthraquinone and 9,10-Anthraquinone-d8
Authors: Pecile Cesare , Lunelli Bruno
Published: January 2005

The infrared spectra of 9,10-anthraquinone and 9,10-anthraquinone-d8 of high isotopic purity have been measured in the 4000–33 cm−1 region both in solution and in the solid. Polarized spectra have been taken on thin layers of oriented crystals grown between KBr plates. Group-theoretical analyses were made for the free molecule (Point Group D2h) and the crystal (Site Group Ci and Space Group P21/a-C2h5). The symmetry species of the observed bands were determined on the basis of the polarized spectra of the crystal. A vibrational assignment of the infrared-active fundamental modes is proposed. The vibrational exciton splittings have been analyzed in detail using dilute isotopic single crystals.
ENDOR Study of Irradiated Histidine HCl
Authors: Box Harold C. , Freund Harold G. , Lilga Kenneth T.
Published: January 2005

Free-radical formation was studied in x-irradiated single crystals of histidine HCl using conventional electron spin resonance (ESR) as well as double-resonance (ENDOR) spectroscopy. The spectra are attributed to a free radical formed by the addition of hydrogen to the C2 position on the imidazole ring of histidine.
Photoemission of Holes from Metals into Anthracene
Authors: Williams R. , Dresner J.
Published: January 2005

Photoemission of holes from metal electrodes into anthracene has been observed for Au, Ag, Al, Pb, and Mg. The photoemission of electrons into the anthracene from these metals could not be observed. From the variation of the photoemission threshold for holes with the work function of the metal a value of 5.80±0.34 eV was obtained for the energy of the valence band below the vacuum level; this value agrees with that determined by photoemission of electrons from anthracene into vacuum. The spectral response of the photoemission is complex; it appears to result from photoemission into a system of narrow bands arising from the interaction of molecular vibrations with a narrow electronic band. The experiment indicates that the energy bands are under 0.1 eV in width, as predicted by theory, and are broadened by vibrational overlap.
Born—Oppenheimer Separation for Three-Particle Systems. II. Two-Center Wavefunctions
Authors: Hunter G. , Pritchard H. O.
Published: January 2005

Semianalytic solutions of the Schrödinger equation for the motion of a particle in the static Coulomb field of two other particles are derived in a form suitable for numerical evaluation of the expansion coefficients on an electronic computer. Relevant mathematical aspects and the numerical methods are described. Tables of two-center wavefunctions are made available through the American Documentation Institute.

An Appendix describes some ``dynamic scaling'' procedures, designed to facilitate Gaussian elimination and bisection where large-order matrices are involved.
Born—Oppenheimer Separation for Three-Particle Systems. III. Applications
Authors: Hunter G. , Pritchard H. O.
Published: January 2005

The formulation of the three-body problem presented in Paper I of this series leads to a set of second-order linear simultaneous differential equations. A numerical procedure for the solution of these equations is described, and is used to compute nonadiabatic energies for the first few rotation—vibration levels of 2Σg H2+, 2Σ HD+, and 2Σg D2+. The dipole moment of 2Σ HD+ is given, together with matrix elements for rotation—vibration transitions.

The method is also applied to obtain approximate binding energies of two-electron atoms and various mesonic systems from two-center wavefunctions.