bluuebunny/crossref_metadata_2025 huggingface dataset:
Destruction of the levels C3Πu (ν′=0, ν′=1) of nitrogen by O2,CO2, CH4, and H2O
Authors: Albugues F. , Birot A. , Blanc D. , Brunet H. , Galy J. , Millet P. , Teyssier J. L.
Published: February 2004

We study the destruction of N2C3Πu(ν′=0 and ν′=1) levels in mixtures N2–O2, N2–CO2, N2–CH4, and N2–H2O at total pressures of several hundred torr. The reciprocal of the time constant for the decay of luminous impulses, measured by time-amplitude conversion, is a linear function of the partial pressures of the two constituents; for instance, τ−1=k1+k2pN2 +kxpx for the ν′=0 level, kx=0.9×10−2 torr−1·ns−1 (O2), 1.16×10−2 (CO2), 1.88×10−2 (CH4), and 1.36×10−2 (H2O). We compare the quenching cross sections obtained from kx with the ones of the kinetic theory. We indicate, lastly, that the energy liberated by C3Πu levels during the collision can be used for the formation of free radicals.
Graph theory and molecular orbitals. VII. The role of resonance structures
Authors: Cvetković D. , Gutman I. , Trinajstić N.
Published: February 2004

The relations between the simplest variants of MO and VB theory are discussed. It is shown that there is a unique principle causing all the cases of congruity between these two theories-Kekulé structures being related to the permutations contained in the molecular graph [Eqs. (6) and (7)]. The class of benzenoid hydrocarbons where both theories are substantially equivalent is rigorously defined using graph theory. A number of topological regularities for these hydrocarbons are proved. Thus, the Dewar-Longuet-Higgins equation, the proof of the Ruedenberg's and Pauling's bond orders, the relation between the VB and MO spin and charge density, and Heilbronner's formula are obtained. The limits of validity for all these results are strictly determined.
Effect of density on the Raman scattering of molecular fluids. II. Study of intermolecular interaction in CO2
Authors: Wright R. B. , Wang C. H.
Published: February 2004

The low frequency intermolecular light scattering in CO2 was studied as a function of the gas and liquid density up to 560 amagats. At low gas density the shape of the observed spectrum can be described qualitatively by a contour describing the pure rotational S-branch spectrum. Significant deviations from the pure rotational spectral shape were observed at increasing density, evolving into that resembling the collision-induced type of the quasiexponential spectral shape found in monatomic fluids at high density. With the temperature properly scaled, the low frequency spectra of liquid and gaseous CO2 at the same density are superimposable. The integrated intensity of the low frequency depolarized Raman spectrum has also been measured as a function of density. An empirical method to correlate the low frequency spectral data is also introduced.
Hydrogen bond studies. 89. A neutron diffraction study of hydrogen bonding in 1-methylthymine
Authors: Kvick Åke , Koetzle Thomas F. , Thomas Robert
Published: February 2004

A neutron diffraction study of 1-methylthymine has been carried out. Intensities of 1681 independent reflections were measured at the Brookhaven National Laboratory High Flux Beam Reactor and the structure was refined to an R(F2) of 0.046. The thymine molecules link to form dimers by means of N–H ··· O hydrogen bonds. The dimers appear to be slightly disordered (∼11%) such that dimers using one or the other of the oxygen atoms as hydrogen-bond acceptors are present in the crystal structure. Evidence is found to suggest the existence of a C–H ··· O hydrogen bond; the H ··· O distance between the methine hydrogen atom in one dimer and the oxygen atom not participating in an N–H ··· O hydrogen bond in a different dimer is 2.045 (3) Å. The C ··· O distance is 3.121(2) Å and the bond is almost linear [∠C–H ⋯ O=170.9(3)°]. The bond distances between heavy atoms are determined to a precision of 0.002 Å or better; the corresponding value for heavy atom-hydrogen atom bond lengths is 0.006 Å.
Crossed-molecular-beam study of the kinematics and dynamics of charge-transfer collisions
Authors: Kaiser E. W. , Crowe A. , Falconer W. E.
Published: February 2004

Using a crossed-molecular-beam apparatus, the low energy product ions formed in a variety of resonant and near-resonant charge-transfer collisions at incident ion energies of 200 eV have been examined. Observation of the translational energy and angular distributions of these low energy product ions confirms that charge transfer takes place at large impact parameters with near-zero momentum transfer.
Electron range studies in solid hydrocarbon films at 77 K
Authors: Chang Y. C. , Berry W. B.
Published: February 2004

Low energy (E <2 eV) photoelectron transmission data have been obtained for thin hydrocarbon films at 77°K as a function of film thickness, which has been varied in steps of 10–70 Å. The photocurrent data approximate exponential attenuation which yield low energy range values which vary from 7 (n-nonane) to 82 Å (neopentane) for very thin films (t <100 Å) and 30 (n-hexane) to 138 Å (neopentane) for thicker films. The origin and interpretation of the exponential distribution as well as the Gaussian distribution which is usually employed, are discussed in terms of Fermi-Age and diffusion models. Two scattering models are discussed as a means of interpreting the two diffusion lengths and the apparent √2 factor between them.
Relationship between solid state charge transfer behavior and molecular structure in a series of 1-(p-substituted phenylazo)-2-naphthols
Authors: Cressman P. J. , Hartmann G. C. , Kuder J. E. , Saeva F. D. , Wychick D.
Published: February 2004

Charge transfer properties of a series of substituted arylazonapthols are shown to correlate with the Hammett's substituent constant σ. For both contact charge exchange of the dyes to metal and field assisted, photostimulated charge transfer from the dyes into nonpolar fluids, the amount of charge transferred is found to increase with increasing σ. However, the efficiency of charge transfer into fluids does not change with σ. In addition the energies of the highest filled and lowest unoccupied molecular levels are shown (by measurement of the oxidation and reduction potentials) to decrease as σ increases. The correlations establish a relationship between charge exchange phenomena and the energy levels of the dyes.
Intramolecular energy transfer in the 4-R-1,2,4-triazoline-3,5-diones: Relation to theory and photochemical reactivity
Authors: Pocius Alphonsus V. , Yardley James T.
Published: February 2004

Various aspects of the intramolecular radiationless decay of the A1A′(1B1) excited electronic state of the 4-R-1,2,4-triazoline-3,5-diones (R-TAD) have been investigated using both laser excited time resolved fluorescence and conventional techniques. The lifetimes of selected vibronic levels of methyl and ethyl TAD under collision free conditions were found to vary approximately linearly from ≃110 to 55 nsec over 2000 cm−1 of excess vibrational energy in the A1A′(1B1) state. Using a somewhat unique technique based upon the fact that vibrational relaxation rather than electronic quenching occurs upon collisions with argon, the quantum yields of fluorescence of selected vibronic levels were determined for methyl TAD and were found to be ≃0.02. Nonradiative rate constants for the selected vibronic levels in A1A′(1B1) of methyl TAD could then be determined and these were found to vary approximately linearly from 8.5×106 to 16.9×106 sec−1 over 2000 cm−1 of excess vibrational energy. Using the experimentally determined variation of the nonradiative rate constant, solution lifetimes, features in the absorption spectrum, and various aspects of the theory of radiationless processes, a choice of the most probable radiationless pathway was made. This choice was intersystem crossing to a lower lying triplet state, either A1A′(1B1) → 3A″(3B1) or A1A′(1B1) → 3A′(3B2) depending upon the R substituent. This choice of nonradiative pathway was found to explain adequately the relative photochemical hydrogen abstraction reactivity of various R-TAD's. It was also found that methyl, ethyl, and n-butyl TAD all display the same fluorescence lifetime of 92±3 nsec at high pressures of inert gas. This is discussed in terms of the radiationless transition theory, which indicates that some vibrational modes do not accelerate the radiationless decay rate over that of the vibrationless level. This is the first reported experimental verification of the presence of vibrational motions that do not participate in radiationless decay.
Infrared spectra of CsCl:BH4− solid solutions
Authors: Schutte W. C. , Coker Howard
Published: February 2004

Solid solutions of borohydride ions in cesium chloride were prepared by diffusion of the borohydride ions into optical grade single crystals. The absorption bands of cesium borohydride in cesium chloride were identified, and the effect of plastic flow on the structure of solid solutions of cesium borohydride in cesium chloride was investigated.
Rayleigh light scattering from ionic solutions and ionic association reactions
Authors: Clarke J. H. R. , Hills G. J. , Oliver C. J. , Vaughan J. M.
Published: February 2004

The spectral distribution of light scattered from ∼1M aqueous solutions of ZnSO4, MnSO4, and CsF has been examined over the frequency range 106–1010 Hz using Fabry-Perot interferometry. Photon correlation spectroscopy has been used to examine aqueous solutions of ZnSO4, MnSO4, and CsF over the range 10–107 Hz. In all cases the spectra could be accounted for by assuming that diffusional concentration fluctuations dominate the scattered light. There was no evidence of additional light scattering from spontaneous chemical exchange reactions in any of the systems investigated and the results reported by previous authors were not confirmed. The photon correlation results could be interpreted in terms of diffusion of solutions components; for ZnSO4, MnSO4, and CsF, the effective diffusion coefficients were 3.8±0.1, 3.3±0.1, and 16.6±2.0×10−6 cm2 s−1, respectively, corrected to 20°C.
Equations of motion method: Inelastic electron scattering for helium and CO2 in the Born approximation
Authors: McCurdy Clyde W. , McKoy Vincent
Published: February 2004

We have applied the equations of motion method to the computation of generalized oscillator strengths in helium and CO2. The equations of motion approach yields excitation energies without the computation of separate ground and excited state wavefunctions and is ideally suited for computing matrix elements of the operator used in the Born approximation. Our results for helium agree well with more extensive calculations [Y. Kim and M. Inokuti, Phys. Rev. 175, 176 (1968)]. We compare our generalized oscillator strengths for CO2 with experiment, and discuss assignments including the peaks at 8.61 and 9.16 eV in the experimental energy loss spectrum. We also compute a valencelike 1Σu+ state below the first ionization potential with a large oscillator strength (f=0.64), which may be responsible for the proposed continuum absorption between 11–14 eV in CO2.
EPR spectroscopic investigations of metal halides doped with transition-metal ions. I. Rhodium(III)-doped AgBr
Authors: Eachus R. S. , Graves R. E.
Published: February 2004

An electron paramagnetic resonance (EPR) investigation of silver bromide doped with Rh3+ ions has revealed that this impurity is an electron-trapping center during exposure. The photoreduction can be effected with white-light exposures, but it is most efficient at 510 and 620 nm. The rhodium(II) photoproduct, [(RhBr6)4−(Agvac+)], is a distorted covalent complex, and the EPR data indicate that this species has a 2A1g (|3z2−r2>) ground state below 100°K, an effective 2B1g (|x2−y2>) ground state between 100 and 220°K, and is dynamically distorting above the latter temperature. An attempt is made to explain this latter observation in terms of the thermally induced reorientation of the associated silver-ion vacancy about the Rh2+ site.
Helium scattering from solid surfaces
Authors: Weare John H.
Published: February 2004

The quantum mechanical scattering of light atoms from well defined solid surfaces is studied via a simplified model of the gas surface system. The differential scattering cross section is calculated using a power series expansion with convergence properties similar to those of distorted wave perturbation theory. The cross section is averaged over the internal states of the system, and the temperature dependence of the one and two phonon contributions is calculated. It is concluded that at sufficiently low surface temperatures and beam energies, one phonon contributions dominate. Comparison of these results with perturbation theory indicates that, for these experimental conditions, a first order perturbation theory should be sufficient to interpret experiments. Arguments are given indicating that this first order calculation may yield direct information about the local density of states of the system. This suggests that He scattering may be developed into an analytical tool, similar to bulk neutron scattering, giving direct information about surface chemical bonding.
Percus-Yevick equation of state for the square-well fluid at high densities
Authors: Smith William R. , Henderson Douglas , Murphy R. D.
Published: February 2004

Values of the distribution functions and thermodynamic properties for the square-well fluid are obtained from the Percus-Yevick theory. Results are reported mainly for high densities and low temperatures and so complement the previously reported results of Levesque and Tago, which were obtained at high temperatures and lower densities. The energy equation of state is found to give the best agreement with the simulation results.
Magnetic properties of silicon and germanium monoxide
Authors: Davis Richard E. , Muenter J. S.
Published: February 2004

Molecular beam electric resonance spectroscopy has been used to study silicon and germanium monoxide in the presence of an external magnetic field. For silicon monoxide the first three vibrational states of 28Si16O were studied giving rotational magnetic moments, |gJ|, of 0.15359(12), 0.15450(11), and 0.15539(12) for v=0, v=1, and v=2, respectively. Similarly, the magnetic susceptibility anisotropies, χ∥ − χ⊥, measured are −3.53(10), −3.66(8), and −3.80(10) kHz/kG2. The molecular quadrupole moment, θ, is calculated to be −1.1(5) esu · cm2. The first two vibrational states of germanium monoxide were studied for the 70Ge16O, 72Ge16O, and 74Ge16O species. |gJ| (70)=0.14179(10), 0.14254(12), |gJ| (72) = −0.14134(11), 0.14208(10), |gJ| (74)= −0.14089(10), 0.14164(12), respectively, for v=0 and v=1. χ∥ − χ⊥ (70)=−4.18(10), −4.26(10), χ∥−χ⊥(72)=−4.17(11), −4.25(11), χ∥−χ⊥(74)=−4.18(9), −4.26(11) kHz/kG2. θ=−4.4(6) esu· cm2. The sign of the dipole moment of GeO is +GeO− assuming gJ <0.
Near ultraviolet n - π transitions of the pyrazine molecule. I. The singlet n - π state and the ground state
Authors: Zalewski Edward F. , McClure Donald S. , Narva David L.
Published: February 2004

The nature of the first n π* excited state of the pyrazine molecule has been investigated by studying the vibrational structure of the spectrum in the region of 3200 Å. The spectrum was observed in the vapor, in the pure crystal, and in crystalline solid solutions in cyclohexane and benzene. The phosphorescence and fluorescence spectra were used to determine ground state frequencies in the various media and to give the Franck-Condon factors of the various modes. Assignments of ν1, ν6a, ν9a, and ν10a in the excited state have been made. It was found that ν10a has a strongly quartic component in its potential function and that there is a large negative anharmonic coupling term between 6a and 10a. These results are interpreted qualitatively in terms of the expected electron redistribution in the n π* state.
EPR of Tb3+, Pr3+, Gd3+, and Eu3+ ions in single crystal La2O2S
Authors: Jewett J. W. , Wigen P. E.
Published: February 2004

Electron paramagnetic resonance measurements of some trivalent rare earth ions in single crystal La2O2S have been performed at low temperatures. At approximately 1.5 K, two sets of four [I=(3/2)] Tb+3 lines have been observed. Site I has a minimum resonance position when the magnetic field is parallel to the c axis and has the following parameters: g∥=4.404±0.008, g⊥ ≈ 0, Δ=0.234±0.004 cm−1, A=0.05±0.002 cm−1. Site II has a minimum resonance position in the a-c plane at an orientation 45° from the c axis and has parameters g∥=17.8, g⊥≈0, Δ=0.18 cm−1, A=0.216 cm−1. In the Tb+3 doped sample, there appears another set of six lines which can be attributed to the hyperfine structure of Pr+3 [I=(5/2)]. The parameters for these lines are g∥=4.1, g⊥ ≈ 0, Δ=0.122 cm−1, A=0.189 cm−1. Studies were also made on the seven-line fine structure spectrum for Gd+3, an S-state ion, for which g∥=1.992 and g⊥ = 1.994. No signals from Eu3+ have been observed.
Spline representation. I. Linear spline bases for atomic calculations
Authors: Gilbert T. L. , Bertoncini P. J.
Published: February 2004

The use of a basis of cardinal splines for atomic calculations with the expansion method is proposed. The basis has the property that the coefficients Cp in the orbital expansion φ (r) = Σp=−1N+1 Cpχp(r) are given by C−1=φ′(r0), Cp=φ(rp), p=0,1, ···, N, and CN+1=φ′(rN), where r0, r1, ···,rN is the mesh of knots on which the spline is defined. The basis functions χp(r) are continuous with continuous first and second derivatives, and may readily be calculated from the expansion χp(r) = Σk=1N Σs=03 rsdk (r)Sksp, where dk(r)=1 if rk−1 ≤ r<rk and 0 otherwise and Sksp is a matrix of coefficients which are uniquely determined by the mesh alone and may be constructed by simple algebraic operations, the most complex being the inversion of a single (N+1)×(N+1) matrix. Atomic Hartree-Fock matrix elements are given by simple polynomial expressions. The number of two-electron integrals increases only as the square of the number of basis functions and can be stored in factored form, so that the storage requirements for the two-electron integrals are trivial. The largest two arrays (equal in size) are the density matrix and the matrix elements of the exchange operator. The results of numerical tests for the hydrogen atom using several different distributions of mesh points are presented. It is found that the number of mesh points required is smaller than for standard numerical methods by a factor of about 4. The accuracy of a linear spline representation with N + 1 knots is comparable to that of a Gaussian expansion with N basis functions.
Formation of O3+ by the reaction of metastable O2+ ions with O2
Authors: Ajello Joseph M. , Pang Kevin D. , Monahan Kevin M.
Published: February 2004

The production of O3+ by the ion-molecule reaction O2+ (a 4Πu) + O2 → O3+ + O was investigated using a photoionization mass spectrometer. The photoionization efficiency for production of O3+ by this reaction was measured from threshold at 742±2 Å (16.71±0.05 eV) to 650 Å (19.07 eV). The appearance potential of the O3+ ion corresponds to reaction of O2+ ions initially formed in the v′=5 vibrational level of the a 4Πu state.
Rate constants for the quenching of N2 (A 3Σu+, vA = 0 – 8) by CO, CO2, NH3, NO, and O2
Authors: Dreyer J. W. , Perner D. , Roy C. R.
Published: February 2004

The techniques of pulse radiolysis and absorption spectroscopy have been used to produce and detect metastable nitrogen (A 3Σu+) in the vibrational levels vA =0–8. Second order quenching rate constants have been determined for a number of additive gases. The rate constants, in units of cm3/sec and for increasing values of vA, are as follows: O2 (1.9±0.3)×10−12; (7.4±0.7) (−12); (5.0±0.3) (−12); (3.4±0.4) (−12); (6.2±0.9) (−12); (5.8±0.5) (−12); (6.5±0.6) (−12); (7.5±3.0) (−12); (5.1±2.0) (−12). CO (1.8±0.5) (−12); (1.8±0.1) (−11); (4.6±0.4) (−11); (2.1±0.3) (−11); (1.9±0.2) (−11); (1.6±0.1) (−11); (1.7±0.2) (−11); (9.0±4.0) (−12); (7.2±0.4) (−12). CO2 (9.9±1.1) (−15); (2.0±0.1) (−14); (1.5±0.2) (−13); (2.9±0.2) (−13); (4.9±0.9) (−13); (1.6±0.2) (−12); (3.1±0.4) (−12); (4.8±0.4) (−12); (4.7±0.2) (−12). NO (2.8±0.5) (−11); (4.0±0.3) (−11); (6.8±0.8) (−11); (1.2±0.1) (−10); (1.1±0.1) (−10); (1.0±0.1) (−10); (9.6±0.7) (−11); (8.9±3.5) (−11); (6.7±0.5) (−11). NH3 (8.2±1.6) (−11); (8.6±2.4) (−11); (1.5±0.2) (−10); (1.2±0.1) (−10); (1.6±0.2) (−10); (1.5±0.1) (−10); (2.3±0.2) (−10); (4.5±1.5) (−11); (1.1±0.1) (−10). An attempt has been made to explain the results in terms of energy transfer processes and to fit the data to a simple model.
On a representation of the equation of state of fluids in terms of the adhesive hard-spheres model
Authors: Barboy B.
Published: February 2004

The solution of the model of adhesive hard spheres in the PY approximation is extended to obtain the equation of state for all temperatures, including the condensed and two-phases region. A simple scheme is given for the determination of the parameters of the model in terms of empirical data for the second virial coefficient.
Interatomic potentials and phonon spectra of dilute rare-gas mixtures
Authors: Cohen Simon S. , Klein Michael L.
Published: February 2004

We have applied existing theoretical results for the impurity induced ir absorption in dilute alloys to study the following rare-gas mixtures: Ar–Ne, Ar–Kr, Kr–Ar, and Kr–Xe. The theory takes into account both mass and force-constant changes, within the harmonic approximation. In evaluating the latter, attempts were made to use realistic pair potentials. We have, surprisingly, identified a resonance mode for an argon crystal doped with neon, and a localized mode in krypton doped with xenon system. The predicted resonance mode agrees well with the observed spectrum of Keeler and Batchelder. Our model for krypton doped with xenon gives rise to a localized mode which happens to fall very close to the band edge. Any attempt to shift this mode far from the band edge would require an unreasonably large change in the force constant around the xenon site. Within the framework of our model and the assumption of randomly distributed impurity atoms, we find it difficult to support the observation of this mode claimed by Obriot et al. However, once allowance is made for the experimental resolution, their in-band recorded spectra for both Kr–Ar and Kr–Xe agree fairly well with the theoretical predictions. On comparing our results for the in-band absorption of the Ar–Kr system, with the experiments of Keeler and Bachelder, we found it necessary to allow for the finite lifetime of pure-lattice phonons even at low temperatures. Such an effect appears to have a profound influence on the relative intensities in different regions of the absorption band. This effect does not appear to have been discussed previously in the literature.
Optical detection of magnetic circular dichroism (ODMCD) for the zero-field microwave transitions of the triplet state
Authors: Gossett E. W. , El-Sayed M. A.
Published: February 2004

Magnetic circular dichroism is detected in the magnetic dipole transitions between the sublevels of photoexcited triplets at 1.6°K utilizing optical detection methods. The theoretical and experimental magnitude of the effect are in excellent agreement. It is demonstrated that when the g factor is positive, a transition which increases in frequency with increasing field will be left-handed circularly polarized while a transition which decreases in frequency with increasing field will be right-handed circularly polarized. The sign of the g factor is determined for the triplet state of several substituted benzenes and is found to be positive in all cases. It is also shown that optical detection of MCD of the triplet state can give the sign of the g factor and the relative order of the zero-field levels but not the absolute order unless it is coupled with the determination of whether the interaction with the microwave field leads to stimulated absorption or stimulated emission processes.
Alkali molecular ion energies and expectation values in a model-potential treatment
Authors: Bellomonte L. , Cavaliere P. , Ferrante G.
Published: February 2004

By using Hellman-type model potentials for alkali atoms, the many-electron problem of the alkali molecular ions is reduced to a three-body problem, and the ground state energy of the these ions calculated in the familiar Rayleigh-Ritz variational treatment. All the ions result as being stable. Other physical quantities (equilibrium and mean distances, etc.) are also calculated. The reported data may be useful in a variety of scattering problems, such as, for instance, alkali atom-ion collisions. They support the James' suggestion that the dissociation energies of the alkali molecular ions must be greater than those of the corresponding molecules, due to the greater diffuseness of the bonding wavefunctions. Application of the present approach to alkali hydride ions seems to indicate that these ions are not stable. The limitations of the pseudopotential approach for molecular calculations are discussed, and it is concluded that the approach is of simpler use for alkali molecular ions than for the corresponding molecules.
Ground and excited states of Ne2 and Ne2+. I. Potential curves with and without spin-orbit coupling
Authors: Cohen James S. , Schneider Barry
Published: February 2004

Ab initio configuration-interaction calculations on ground-state Ne2, the excited Σu,g+1,3 and 1,3Πu,g states of Ne2 formed from Ne(3s; 1,3P) and Ne(1S), and the Σu,g+2 and 2Πu,g states of Ne2+ have been carried out. The dissociation energies of the Σu+1,3 excited states of Ne2 were found to be considerably smaller than that of the corresponding molecular ion. Potential maxima were found in the attractive interactions of the excited Ne2 molecule. A semiempirical model, based on the observed atomic splittings, is given for treatment of spin-orbit coupling effects. The adiabatic potential curves resulting from diagonalization of the spin-orbit interaction were found essential to the understanding of spectroscopic observations. Estimates of the long-range dispersion interactions are also presented.
Ground and excited states of Ne2 and Ne2+. II. Spectroscopic properties and radiative lifetimes
Authors: Schneider Barry , Cohen James S.
Published: February 2004

Using the wavefunctions and potential curves for Ne2 and Ne2+ and the semiempirical model of molecular spin-orbit coupling discussed in the preceding paper, spectroscopic analyses and lifetime calculations have been carried out. The calculation of lifetimes for excited states of Ne2 allows for both bound-bound and bound-free transitions. Since the Franck-Condon overlaps between the ground and excited bound states are generally small, bound-free transitions dominate. The lifetimes determined for the ground vibrational states of the 1u(3P2), 0u+(3P1), and 0u+(1P1) states of Ne2 are 11.9 μs, 2.8 ns, and 1.2 ns, respectively. However, it should be noted that some transition moments show a large variation as a function of internuclear distance, and consequently the lifetimes of different vibration levels of the same electronic state may differ significantly.
How to resolve the orbital ambiguity to obtain the orbital set which is stable to an excitation
Authors: Hirao Kimihiko
Published: February 2004

We discussed how the orbital ambiguity in general SCF theory can be removed to obtain the orbital set which is stable to an excitation. The orbital ambiguity for the ground state wavefunction can be resolved while at the same time performing the configuration interaction calculation for the specific singly excited states. That is, the orbitals can be uniquely determined so that they have the physical significance that they satisfy particular types of the Brillouin conditions for the excited states considered in addition to the Brillouin theorem for the ground state. This implies that the definition of Huzinaga's potential to obtain meaningful virtual orbitals is generalized to include wavefunction for open-shell systems.
Generalized mean spherical approximations for polar and ionic fluids
Authors: Ho/ye J. S. , Lebowitz J. L. , Stell G.
Published: February 2004

Generalized mean spherical approximations are solved for polar and ionic fluids. They are generalizations of previous mean spherical results in the sense that more general forms for the direct correlation function c(12) are considered than heretofore. In the case of a polar fluid, c(12) outside a hard-sphere core is taken to be a sum of an ideal dipole term, a Yukawa term, and two short-ranged terms, one of which is a shielded dipolar interaction, the other of which is a shielded ``classical Heisenberg'' interaction. In the ionic case, c(12) outside the core is taken to be the sum of Coulomb and Yukawa terms. In both cases, the coefficients of all terms can be independently adjusted. Two applications of our generalized mean spherical results are discussed. The first generates improved approximations with built-in thermodynamic consistency. The second is a more straightforward use of the generalization to provide mean spherical approximations for a wider class of potentials.
Satellite bands in the spectrum of mercury in the presence of argon, krypton, and xenon
Authors: Kielkopf J. F. , Miller R. A.
Published: February 2004

New measurements of satellites of mercury spectral lines in the presence of argon, krypton, and xenon are reported. While a few satellites appear on some lines, not all lines show distiguishable intensity maxima in the continuum adjacent to the pressure broadened line. Features previously reported in the case of the 2536 Å resonance line are confirmed for argon and krypton. New results are reported for xenon. In addition, detailed measurements of the Hg–Ar, Hg–Kr, and Hg–Xe vibrational spectra that appear near 2536 Å are reported and partially analyzed. Evidence pointing to the origin of the 2536 Å violet satellites as due to collisions between free atoms rather than bound pairs is also discussed.
Structure of the liquid alkali metals by an optimized iterative solution of the Percus-Yevick equations
Authors: Leribaux Henri R. , Miller Laurence F.
Published: February 2004

The structure of the liquid alkali metals is obtained by an optimized iterative solution of the Percus-Yevick theory and by using recent pseudopotential models and screening functions for these metals. This solution involves an optimized expression for the correction function to g(r), knowing one guess and one calculated result for g(r). This is obtained by setting a weighted residual corresponding to the Percus-Yevick equation equal to zero. The residual is evaluated to first-order in a change in this correction function. This is usually a good approximation after the first few iterations where a more restrictive expression for the correction function is proposed. Convergence of this optimum iteration procedure to an error of 0.1% in the norm of the correction function is accomplished within 100 iterations. Complete results are presented for the five liquid alkali metals near their melting point. The method gives a successful qualitative check of the effective Ashcroft-Singwi potentials used (initially obtained from a best fit to the force constants in the solid alkalis), particularly in K, Rb, and Cs.
Assignments in the ultraviolet spectra of MoF6 and WF6
Authors: McDiarmid Ruth
Published: February 2004

The ultraviolet absorption spectra of gaseous MoF6 and WF6 were measured from 1100 to 2500 Å (40 000–90 000 cm−1). Assignments of the observed transitions, based on a qualitative molecular orbital diagram and comparisons of predicted and observed relative band intensities, are proposed. The ligand field splitting of the Mo(4)d orbitals is estimated to be 40 000 cm−1. A comparison of the uv absorption and photoelectron ionization spectrum of WF6 suggests that for this molecule the ligand field approximation is excellent: There are no interactions between the ligand and metal orbitals. Many of the observed transitions manifest progressions in the a1 vibrational mode from which expansions of the molecular octahedron in each of the assorted electronic excited states is deduced.
Quantum effects on the dielectric virial coefficients of polar gases
Authors: MacRury Thomas B. , Steele William A.
Published: February 2004

General expressions are written for the second virial coefficient and the second dielectric virial coefficient of a gas made up of polar, polarizable, nonspherical molecules. The results obtained include the first correction terms due to translational and to rotational quantum effects, and it is argued that the rotational terms can be appreciable in some important experimental systems. Numerical values of both the classical virial coefficients and the first quantum corrections have been calculated for a model potential function including polarizable dipole energies and an angle-independent Lennard-Jones potential. The results are tabulated for a range of the parameters.
ESR and INDO study of radical conformations in irradiated single crystals of L-histidine free base
Authors: Westhof Eric , Flossmann Wolfgang , Lüdemann Hans-Dietrich , Müller Adolf
Published: February 2004

Radicals produced in x-irradiated single crystals of L-histidine free base in the temperature range 77–300 K have been investigated using ESR spectroscopy at 9.5 and 35 GHz. The main species trapped at 77 K are radical anions located at the carboxyl group. These are converted to deamination radicals upon warming. Conversion of the anion into the deamination radical is not found if the former is bleached by uv illumination at 77 K. At room temperature, only radicals resulting from deamination are observed. Two different conformations of the deamination have been found. The one obtained at room temperature is produced from a precursor with identical composition but different conformation. The latter, which is stable at reduced temperatures, is in the open conformation like both the precursor anion radical and the parent molecule. The room temperature radical however adopts a closed conformation. The identifications are supported by MO-SCF calculations at the INDO level. A detailed analysis of the anion radical and the deamination radical by INDO is presented.
Mechanism of the bimolecular(?) hydrogen-iodine reaction
Authors: Anderson James B.
Published: February 2004

A combined phase-space/trajectory study of the hydrogen-iodine exchange reactions (overall, H2+I2→HI+HI) was carried out for a LEPS potential energy surface modified to favor reaction through the collinear reaction configuration. The results show reaction to occur by both bimolecular and termolecular mechanisms involving pairs of iodine atoms with energies slightly below (bimolecular) or slightly above (termolecular) the dissociation limit. Together with other considerations this finding suggests that in stating the reaction proceeds by the bimolecular mechanism the old textbooks may have been correct. A detailed comparison with Sullivan's photochemical experiments requires a knowledge of the iodine-atom recombination process which is not presently available. Sullivan's primary conclusion, i.e., the iodine species participating in the exchange reaction are the same as those in the slow step of recombination, is upheld; but, the experimental distinction between bimolecular and termolecular mechanisms depends on the question of the relative rates of recombination and relaxation of iodine.
Reduced fermion density matrices. II. Electron density of Kr
Authors: Yuan Jian-M. , Lee Soo-Y. , Light J. C.
Published: February 2004

The methods used to evaluate the inverse velocity function (∂P)/(∂E) ≡ PE(x,E) are briefly reviewed. The N-fermion density formula of Light and Yuan is found to give the best results when smooth, bounded, and everywhere positive quantum momentum, and PE functions are used. The latter is tested on the model problem of noninteracting fermions in a Coulomb potential. Except for the s-state sum, where an ad hoc correction is prescribed near the nucleus, the good results serve as a motivation for an approach to an SCF calculation for Kr. There is an indication that the Fermi energy may be used as a criterion for self-consistency or convergence of the charge density and potential.
Microwave optical double resonance of NO2 with a tunable cw dye laser. II. Excited state microwave transitions
Authors: Tanaka Takehiko , Field Robert W. , Harris David O.
Published: February 2004

Microwave transitions in the 2B2 electronic excited state of NO2 were observed by microwave optical double resonance (MODR) spectroscopy using a tunable, single frequency, continuous wave dye laser as an optical pump. Various spin and hyperfine components of the 909–818 microwave transition in the 2B2 state were identified, and the spin splittings and the hyperfine structure were precisely determined. Interesting pressure dependence of the MODR signal for the 909–818 transition was found and analyzed in terms of a three-level steady state kinetic treatment of microwave optical double resonance. The analysis shows that the 818 level has considerably lower photon yield for photoluminescence than the 909 level. In addition to the 909–818 transitions, three groups of mystery transitions originating from the 909 or 818 level were unexpectedly detected. The final levels of these transitions cannot belong to the same vibronic state as the 909 and 818 states. A reasonable explanation is that the mystery transitions are perturbation induced microwave transitions from levels of the 2B2 state to levels of a longer lived electronic state. Different photon yields of the 909 and 818 rotational levels of the 2B2 state are also understood by perturbations between the 2B2 and the longer lived electronic state.
Gas-dynamic corrections applied to laser-induced fluorescence measurements of HF (v = 1) and DF (v = 1) deactivation
Authors: Bott Jerry F.
Published: February 2004

Partial-pressure measurements in laser-induced fluorescence measurements have been corrected for gas-dynamic effects. These corrections bring a number of HF (v = 1) deactication measurements into close agreement.
Microwave spectrum of (trifluoromethyl)germane, CF3GeH3
Authors: Krisher Lawrence C. , Watson William A. , Morrison John A.
Published: February 2004

Microwave spectra of five isotopic species of CF3GeH3 have been investigated in the region 15 000 to 31 000 MHz. The height of the potential barrier hindering the internal rotation was determined to be 1280±150 cal/mole, using the frequency method for rotational satellite transitions. The sym-sym case of hindered internal rotor molecules is discussed, and expressions are given for calculating barrier heights using tabulated quantities.
Nonradiative transitions in the first excited singlet state of perfluorocyclobutanone: Fluorescence decay times and fluorescence excitation spectroscopy
Authors: Lewis Roger S. , Lee Edward K. C.
Published: February 2004

Fluorescence decay times (τF) of an ``isolated'' molecule of perfluorocyclobutanone (PFCB) in its first excited singlet state (S1) with little vibrational energy content and that of a vibrationally relaxed species are 110±4 nsec; the nonradiative lifetime is 112 nsec and the radiative lifetime is 5.4 μsec. These low energy PFCB (S1) species decay chiefly via the S1↝ T1 intersystem crossing route. The value of τF (λex=3577 Å) at ``low pressure'' is 49 nsec, indicating the probable existence of a new electronic relaxation channel below λex=3800 Å. Fluorescence excitation spectroscopy at ``low pressure'' provides the intrinsic fluorescence quantum yield (φF) as a function of exciting wavelength, and it was found that φF begins to decrease below 3800 Å and it is reduced by a factor of 100 below 3480 Å. Collisional lengthening of the τF values at λex=3577 Å indicates that ≤ 1 kcal/mol is lost per collision with a PFCB (S0). From the overlap of the absorption and emission spectra, the 0–0 band of the first singlet n-π* transition is estimated at 4100 Å.
ESR study of paired radicals in irradiated single crystals of n-eicosane
Authors: Hamanoue K. , Kamantauskas V. , Tabata Y. , Silverman Joseph
Published: February 2004

The pairwise trapping of radicals in γ- and proton-irradiated single crystals of n -eicosane was followed by electron spin resonance measurements. Spectra due to both the ΔMs = 1 and ΔMs = 2 transitions were found. The ΔMs = 1 spectra of the radical pairs show the same hyperfine splitting as that of the ΔMs = 2 spectra. From the spectrum of the ΔMs = 1 transition of paired radicals, the maximum separation due to the zero field splitting in the plane perpendicular to the chain axis was determined to be 287 G; from this the distance of the paired radicals was estimated to be 5.55 and/or 5.67 Å. By the rotation of the crystal axis, 11 peaks change to 22 peaks, indicating that there exist two types of paired radicals. Also the decay of the two types of radical pairs show different temperature dependence. The types of paired radicals are probably in the form of two alkyl radicals on adjacent hydrocarbon chains. The value of 5.55 Å is consistent with the intercarbon distance between two adjacent chains aligned along the direction of the a axis; the 5.67 Å value is consistent with the intercarbon distance between two adjacent chains aligned in the b direction. In addition the LET effect was investigated. The yield of paired radicals appears to be related to the yield of blobs and short tracks.
Multiple scattering method based on overlapping atomic spheres with application to the TCNQ molecule
Authors: Herman Frank , Williams Arthur R. , Johnson Keith H.
Published: February 2004

The theoretical foundation of the self-consistent statistical exchange (X α) multiple scattering method based on overlapping atomic spheres is presented. After discussing the principal assumptions and approximations, the theory is illustrated by a study of the electronic structure of the TCNQ molecule. Satisfactory results are obtained for the energy level structure and electronic charge distribution if the atomic sphere radii are chosen in accordance with the following guidelines: (a) the calculated first ionization energy should agree with experiment; and (b) the calculated virial coefficient should be equal to −2. The present work suggests that the overlapping sphere model can be used to obtain realistic electronic structures for large planar organic molecules as well as for arrays of such molecules.
Perturbation corrections to Koopmans' theorem. III. Extension to molecules containing Si, P, S, and Cl and comparison with other methods
Authors: Chong Delano P. , Herring F. Geoffrey , McWilliams Denis
Published: February 2004

The method of ordinary third-order Rayleigh Schrödinger perturbation theory together with the geometric approximation is used to evaluate the vertical ionization potentials of HCl, H2S, H3P, H4Si, H3SiF, and H3CCl. The ``1 1/2-zeta'' STO basis set employed permits excellent agreement between theory and experiment to be attained. Computations on H2O, N2, and F2 using GTO basis sets show that the present method is equivalent to the many-body techniques employed by other workers.
Vibrational spectrum and force field of uranium hexafluoride
Authors: McDowell Robin S. , Asprey Larned B. , Paine Robert T.
Published: February 2004

A total of 44 bands in the infrared and Raman spectra of 238UF6 vapor has been measured using long-path absorption cells and multiple-reflection Raman cells. The types of contours exhibited by these bands, and analogous contours in the spectrum of SF6, are discussed. Overtone and combination bands with resolved Q branches are used to estimate the anharmonicity corrections for the stretching fundamentals. The infrared contours of ν3 (at 228 K) and ν4 (at 256 K) have yielded estimates for the Coriolis constants ζ3 and ζ4 that satisfy the sum rule. The 235UF6–238UF6 frequency shifts in these fundamentals have also been measured. All of these data, plus vibrational amplitudes from the electron diffraction study of Seip, have been combined to determine the general quadratic harmonic force field of UF6. Only three valence force constants are appreciably different from zero: fr=3.85±0.05, fα≈fα−fa′a= 0.12±0.01, and frr (cis interaction)=0.30±0.02, all in mdyn/Å. The large differences between this force field and that previously determined for WF6 are attributed to the effects of f-orbital contributions in UF6.
Electronic and geometric structure of the free XeF6 molecule
Authors: Nielsen U. , Haensel R. , Schwarz W. H. E.
Published: February 2004

The absorption spectrum of gas phase XeF6 (from Ljubljana Fluor Chemistry Institute) was investigated in the region from 50 to 170 eV using the synchrotron radiation of DESY. We did not succeed in finding further evidence for the electronic isomers hypothesis of Goodman. Our spectrum can be explained if we assume that at room temperature XeF6 consists of only one molecular species of slightly distorted Oh geometry (Bartell and Gavin model). Nearly all other experimental results are consistent with this.
Perturbation effects on lifetimes in N2+
Authors: Dufayard J. , Negre J. M. , Nedelec O.
Published: February 2004

Variation of lifetimes induced by a perturbation have been measured by the phase-shift technique. The transition studied is B 2Σu+ → X 2Σg+ in N2+, where perturbations occur in several bands between B 2Σu+ and A 2Πu. The perturbed lifetimes measured on selected rotational lines of the 1→2 band are found to increase from 60 to 90 ns in agreement with the values calculated from the nonperturbed lifetimes and the relative energies of the interacting levels.
Polymer viscosity in concentrated solutions
Authors: Freed Karl F. , Edwards S. F.
Published: February 2004

Our previous theory of polymer viscosity (which completely incorporates hydrodynamic interactions) is generalized to the case of polymer solutions at finite concentration. The specific viscosity of the polymer solution is expressed in a multiple scattering type cluster expansion which is formally in powers of the polymer concentration. We explicitly treat the case of concentrated solutions or the case of undiluted polymers in the absence of entanglements. It is shown that the presence of the other polymers leads to a screening of the intrachain hydrodynamics interactions when the natural size of a free polymer chain becomes on the order of the average volume available per chain in solution. We show how the screening is responsible for the transition from a polymer intrinsic viscosity which varies as M1/2 (M is the polymer molecular weight) in the infinitely dilute limit to a Rouse-like specific viscosity which varies as M in the concentrated limit. It should be noted that the screening cannot be described if the popular preaveraging approximation is employed for the hydrodynamic interactions.
Spin coupling of two identical complex ions. I. Theory
Authors: Amoretti G. , Varacca V.
Published: February 2004

By means of a Heitler-London procedure, theoretical expressions for the ESR parameters of a pair of identical complex ions with spin S =(1/2) are derived. The conditions for spin coupling and for a disalignment of the g and fine-structure tensors are discussed. The calculation of the contributions of the dipolar and exchange interactions, respectively, shows that the last one, which causes the singlet-triplet energy separation, gives anisotropic contributions to the zero-field splitting, owing to the effect of the spin-orbit coupling. Moreover, such contributions are in competition with those of the dipolar interaction. The crucial importance, for the exchange interaction, of a mixed ground state is shown. Its dependence on the form of the ligand orbitals is also pointed out.