bluuebunny/crossref_metadata_2025 huggingface dataset:
Delocalization of electronic energy in the lowest triplet states of molecules
Authors: Hemminger John C. , Wicke Brian G. , Klemperer William
Published: February 2003

A variety of molecules are examined for the existence of metastable (τ≳1 msec) electronic states under isolated molecule conditions. A beam is excited by electron impact and detected after a 1 msec drift by Auger electron emission from a cesium surface. Metastable states were observed for benzene, toluene, m-xylene, acteylene, cyanogen, SO2, N2, and CO. Molecules observed to not have metastable electronically excited states were formaldehyde, acetone, cyclohexanone, 2-cyclopenteneone, 2-cyclohexeneone, bromobenzene, benzylbromide, propyne, hydrogen cyanide, acetonitrile, carbon dioxide, carbon disulfide, carbonyl sulfide, ammonia, ethylene, 1,3-butadiene, cis-2-butene, trans-2-butene, cyclopentene, cyclohexene, cyclopropane, and allene. A correlation is observed between nonmetastability of the lowest triplet state and a large change in geometry between the ground electronic state and the lowest triplet state. Mixing of the lowest triplet state of a molecule with high vibrational levels of the ground electronic state is discussed in light of the experimental findings. The generalized Franck–Condon factors of the presently accepted theory of radiationless transitons are found to be the crucial factors which determine the metastability or nonmetastability of the lowest triplet state of most molecules. Cross sections for production of high vibrational levels of the ground electronic state (Evib≳20 000 cm−1) by electron bombardment excitation of a triplet state which is strongly coupled to these levels of the ground state may be as large as a few tenths of a square angstrom.
Some aspects of benzene vapor phase photochemistry
Authors: Lee San Ardi , White John M. , Noyes W. Albert
Published: February 2003

The fluorescence, triplet state, and isomerization yields from benzene vapor have been determined at several wavelengths but principally at 266.8 nm, where 1B2u molecules are formed in the zeroth vibrational level. The fluorescent yield at 266.8 nm varies little with pressures from 1 to 20 torr, but at higher pressures of either benzene or inert gases the yield decreases slowly to about 0.18, i.e., the same yield as obtained at 253 nm and pressures over about 15 torr at room temperature. Triplet yields were determined by the biacetyl method, and at low pressure the sum of the fluorescence and triplet yields at 266.8 nm was about 0.97. At shorter wavelengths the sum increasingly differs from unity and the difference is almost certainly due to isomerization. Primary isomerization yields are difficult if not impossible to measure quantitatively because of the photochemical and possibly the thermal instability of benzvalene, the predominant isomer formed at these wavelengths. Within experimental error there is no isomerization at 266.8 nm and the steady state concentration of benzvalene increases with decreasing wavelengths in general. The presently known facts about the photochemistry fit into a reasonably consistent picture, but more data along certain lines are badly needed even if they would be very difficult to obtain.
Critical effects of the light scattering intensity at an order–disorder phase transition: KCN
Authors: Dultz W.
Published: February 2003

The temperature dependence of the Raman spectrum of potassium cyanide between 140 and 220 cm−1 was measured in the two low temperature phases. With decreasing temperature the band at 190 cm−1 grows out of a broad feature of the spectrum and becomes distinct below the transition temperature at 83 °K. We suppose that the Raman spectrum of KCN in the measured energy range is disorder induced above 83 °K, and thus of low intensity. Below the transition temperature only the intensity of the Raman allowed modes increases. We analyze the data by assuming that fluctuating clusters of the ordered low temperature phase enhance the intensity of these modes. From the spectra we determine the critical exponents ν=0.68 and β=0.33 and estimate a lower limit for the correlation length.
The rotational Zeeman effect in methyl vinyl ether
Authors: Duda L. E. , Flygare W. H.
Published: February 2003

The molecular rotational Zeeman effect is reported for methyl vinyl ether. The molecular g values are gaa=−0.0868±0.0005, gbb=−0.0224±0.0002, and gcc=0±0.0005. The magnetic susceptibility anisotropies (in units of 10−6 erg/G2 mol) are 2χaa−χbb−χcc=8.0±0.6 and 2χbb−χaa−χcc=3.4±0.5. The molecular quadrupole moments (in units of 10−26 esu cm2) are Qaa=2.8±0.5, Qbb=0.8±0.5, and Qcc=−3.6±0.9.
Chemiluminescence spectra of ScO and YO: Observation and analysis of the A′ 2Δ–X 2Σ+ band system
Authors: Chalek Carl L. , Gole James L.
Published: February 2003

A new band system between 6200 and 7500 Å has been observed in the ’’single collision’’ beam–gas chemiluminescent spectrum resulting from the reactions of Sc and Y atoms with O2. A strong, well-developed system is observed in the YO spectrum resulting from the Y–O2 reaction. A vibrational analysis of two distinct subsystems, each consisting of double-headed bands (ΔΛ?1), yields Te=14 531.2 cm −1, ωe′=794.0 cm−1, ωexe′=3.23 cm−1, ωe″=861.9 cm−1, ωexe″=2.95 cm−1 for the lower component, and Te=14 870.4 cm−1, ωe′=794.9 cm−1, ωe′=3.3 cm−1, ωe″=862.1 cm−1, ωexe″=3.025 cm−1 for the upper component. Semiempirical calculations predict Te=15 330.4 cm−1 for the A′ 2Δr state of YO. Perturbation calculations predict that mixing of the A 2Π state with the A′ 2Δ state of YO may be as large as 3.5%. On the basis of these calculations, the new band system is attributed to the A′ 2Δ–X 2Σ+ transition of YO. The new band system in the Sc+O2 spectrum is weaker and not as well resolved as the YO system. However, analysis of the system, by analogy with that of YO, yields T0=14 965.9 cm−1, ΔG′1/2 =834.0 cm−1 for the ScO A′ 2Δ3/2 state, and T0=15 072.0 cm−1, ΔG′1/2=837.0 cm−1 for the ScO A′ 2Δ5/2 state.
Inelastic cross sections for molecules interacting through dipole and/or quadrupole potentials
Authors: Biolsi Louis
Published: February 2003

Formal expressions for the lowest order inelastic contribution to the degeneracy averaged total cross section for both distinguishable and indistinguishable rigid diatomic molecules are obtained for molecules interacting through a multipole potential. Explicit expressions for the inleastic cross section are obtained for molecules interacting through permanent dipole–dipole, dipole–quadrupole, or quadrupole–quadrupole potentials. These results require the summation over only a single quantum number; the relative angular momentum quantum number. Thus, they are useful for analytic or numerical calculations.
Hindered rotational energy levels of a tetrahedron in a trigonal crystalline field
Authors: Smith David
Published: February 2003

The energy levels for the motion of a rigid tetrahedral molecule in a trigonal crystalline field have been computed. The symmetry group of the Hamiltonian is ?×C3, where ? is the tetrahedral group of rotations about body-fixed axes and C3 is the trigonal group of rotations about space-fixed axes. The effect on the tunneling frequencies, heat capacity, and activation energy of lowering the symmetry of the crystalline field from tetrahedral to trigonal is discussed. The energy levels of a symmetric top molecule in a tetrahedral crystalline field have been computed and used to determine tunneling frequencies.
Translational energies from ionic fragmentation
Authors: Carter Duane E.
Published: February 2003

Statistical theories of unimolecular reactions are applied to determine the translational energies of fragments of ionic decomposition. The results are found to be in conflict with experimental measurements of translational energies of ions formed by electron or photon impact. However, a full application of phase-space theory results in much better agreement with ion–molecule experiments than the theory of Safron et al. [S. A. Safron, N. D. Weinstein, D. R. Herschbach, and J. C. Tully, Chem. Phys. Lett. 12, 564 (1972)]. A classical model of a triatomic molecule is constructed, and the partitioning of energy in dissociating trajectories is examined and compared to statistical theories. Discrepancies between the trajectories and statistical theories are noted and possible explanations discussed.
The effect of infrared laser excitation on reaction dynamics: O+C2H4† and O+OCS†
Authors: Manning Ronald G. , Braun Walter , Kurylo Michael J.
Published: February 2003

A technique involving flash photolytic production and resonance fluorescence detection of O atoms coupled with cw production of vibrationally excited reactant molecules using a CO2 laser is described. The method relies on the high sensitivity and precision of the flash photolysis resonance fluorescence technique to compare reaction rates measured with the laser off with those measured with the laser on, thereby assessing any effect of reactant vibrational energy on the dynamics of the chemical reaction. The limiting value of the laser enhancement that can be discerned depends ultimately on two factors: (1) the equilibrium concentration of vibrationally excited reactant that can be experimentally realized (i.e., absorption of laser flux vs deactivation losses), and (2) the magnitude of the activation energy for the thermal reaction. This determines the extent of a purely thermal (heating) effect. We observed little or no effect of vibrational energy in C2H4 on the rate of reaction with O atoms. Because of a somewhat higher activation energy, it was considerably more difficult to measure an effect in the O+OCS reaction. Within the limits of detectability, all observations in this system could be attributed to heating effects. A factor of 1.5 increase in the rate constant for O+C2H4† over that for O+C2H4 and a factor of 3 for O+OCS† over O+OCS would have been detectable in these experiments. The results seem to indicate that there is little or no coupling of vibrational energy to the reaction coordinate leading to activated complexes in these two reaction systems.
Extended time dependent Hartree theory of van der Waals interaction: Inclusion of electric quadrupoles
Authors: Rabenold David A. , Linder Bruno
Published: February 2003

Expressions are derived for the van der Waals interaction free energy, to infinite order, which include dipole and quadrupole interactions. The treatment is an extension of the time-dependent Hartree approximation developed previously for dipolar interactions. The results are obtained via linear response theory. Just as in the dipolar case, the results are expressed in terms of the eigen frequencies of a normal mode matrix. In the present formulation, however, the normal modes are determined not only by electric dipolar coupling but also by coupling of electric quadrupoles with each other and with dipoles. The method is also useful in generating the perturbation terms of the free energy shift. It is found that the second order term, when applied to isotropic oscillators at zero degrees, reduces to the result derived earlier by Margenau. The nonadditive three-body potential, derived here, reduces to the Axilrod–Teller triple dipole potential in the absence of quadrupoles. Numerical results are given for the interaction between two and between three isotropic oscillators.
Alkyl–metal surface complexes: Methyl and lithium
Authors: McLean W. , Pedersen L. G. , Jarnagin R. C.
Published: February 2003

Clusters containing 4 and 10 atoms of lithium interacting with methyl groups were investigated as models for alkyl–lithium surface complexes. Pople’s ab initio Gaussian 70 procedure was used to optimize geometrical arrangements starting from sites having a C3v site symmetry and selected on the basis of known chemical and physical properties. Two sites were identified as rational possibilities for binding of methyl to lithium surfaces. One of the two sites was calculated to be about 40 kcal more favorable than the other. Both sites are prevalent on Li(111). The position of CH3 above Li(111) and orientation of CH3 relative to the Li surface network, as well as binding strengths, orbital parentage, and charge distributions were qualitatively the same on both 4 and 10 atom models of substrate. The change in quantitative factors among the 4 and 10 atom models suggest that 7 to 13 atoms in the substrate are sufficient to approximate properties of surface complexes of lithium with alkyl hydrocarbon groups. A potential surface for motion of CH3 on Li(111) estimated with 10 points suggests that an activation energy of 35–40 kcal is to be experienced for associative desorption of methyl to ethane.
Test of inert gas interatomic potentials: Virial coefficients for argon adsorption on xenon-plated graphite
Authors: Brown David G. , Hsue C. S.
Published: February 2003

Virial coefficients have been calculated for argon adsorption on xenon-plated graphite. Good agreement for the lowest order coefficients is obtained using the accurate inert gas interatomic potentials currently available. Agreement with the higher order coefficients is still poor, however, implying the necessity of either the inclusion of additional effects or reinterpretation of the experimental data. The discrepancies occasioned by the former use of 6–12 potentials are examined, and the result of including three-body terms is considered.
Photodissociation spectroscopy of CO3−
Authors: Moseley J. T. , Cosby P. C. , Peterson J. R.
Published: February 2003

The photodissociation cross section of gas-phase CO3 − has been measured over the wavelength range from 4579 to 6940 Å, and reveals detailed structure reflecting the vibrational spacings of a predissociating excited electronic state. From an analysis of the structure, we identified three vibrational modes of the excited state having energies of 990, 1470, and 880 cm−1. The bond energy D (CO2–O−) of the ground state CO3− was determined to be 1.8±0.1 eV, and the electron affinity of CO3 was found to be 2.9±0.3 eV. By comparison with theoretical calculations, the lowest predissociating state was identified as 1 2A1. Observations regarding other excited states of CO3− are made.
Exact static dipole polarizabilities for the excited S states of the hydrogen atom
Authors: McDowell Keith
Published: February 2003

The exact static dipole polarizabilities for the excited S states of the hydrogen atom are determined by using the reduced free-particle Green’s function method developed by McDowell and Porter [J. Chem. Phys. 65, 658 (1976)]. The general formula for the polarizabilities is found to be α1 (n)(S) =n4(2n2+7)/2.
An NMR study of molecular reorientation processes in solid n-butane
Authors: Hoch M. J. R.
Published: February 2003

Proton magnetic resonance line shapes for polycrystalline n-butane have been studied over the temperature interval 20 K to the melting point. Spin–lattice relaxation time measurements have been made in the low temperature solid phase but no minimum found. The results show that methyl group tunneling persists to very low temperatures at a rate sufficiently high to narrow the absorption spectrum. In the high temperature solid phase long axis rotational motion of the molecules occurs. A model for this form of motion is discussed.
Higher time derivatives of the generalized entropy
Authors: Bulsara Adi R. , Schieve W. C.
Published: February 2003

Using the generalized N-body expression for a Liapunov functional developed by Prigogine, George, and Henin, a condition is obtained whereby the successive time derivatives of this functional alternate in sign for weakly coupled systems. This condition is applied and seen to hold true for generalized Bose and Fermi systems. An N-body entropy is defined in terms of this functional, which contains diagonal as well as off-diagonal elements of the density matrix. This ’’generalized entropy’’ is seen to be concave close to equilibrium, similar to the results of Harris. It does not appear that this property holds for the entropy far from equilibrium.
1H and 11B NMR study of molecular reorientation in crystalline 9-bromo-m
e
t
a-carborane
Authors: Leffler A. J. , Alexander M. N. , Sagalyn P. L.
Published: February 2003

1H and 11B NMR have been used to characterize molecular reorientation in crystalline 9-bromo-meta-carborane. A structural phase transition has been found at 344±2 K. In the high temperature (α) phase, reorientation is rapid and apparently isotropic, with activation energy EA=22.4±1.3 kJ/mol. In the low temperature (β) phase, reorientation is anisotropic, with an apparent activation energy of 47.0±6.3 kJ/mol for temperatures above the proton T1 minimum (∼300–344 K), and 14.7±1.3 kJ/mol for temperatures below the T1 minimum (∼230–290 K). Temperature dependences of the linewidths and shapes in the β phase are tentatively interpreted to indicate a more complicated reorientation than was observed in ortho-carborane.
Photodissociation of C4H8+ ions: Comparison of experimental branching ratios with unimolecular decomposition theory
Authors: Riggin M. , Orth R. , Dunbar R. C.
Published: February 2003

Upon irradiation by a 2.5 kW xenon arc lamp, 1- and 2-butene cations were observed to photodissociate to C2H4+, C3H3+, C3H5+, and C4H7+. An ionic lifetime limiting technique was used with an ICR spectrometer to eliminate largely the effect of ion–molecule reactions on the photofragementation pattern and to obtain quantitative measurements of the relative yields of the various dissociative channels. A unimolecular decay model was found to describe adequately the wavelength dependence of the relative C4H7+ and C3H5+ yields.
Molecular beam study of the HeNe-laser pumping transition
Authors: Haberland Hellmut , Oesterlin Peter , Schmidt Konrad
Published: February 2003

The red line of the helium–neon laser is pumped by the excitation transfer from a metastable He atom to ground-state Ne atoms, He(2 1S)+Ne→He+Ne(3s). This process is studied in a crossed molecular beam apparatus. (AIP).
Pressure dependence of the proton NMR chemical shift in liquid water
Authors: Linowski J. W. , Liu Nan-I , Jonas J.
Published: February 2003

Measurements of the NMR proton chemical shift in liquid water are reported as a function of pressure (upto 4 kbar) at temperatures of 0°, 20°, 50° and 100°C.(AIP)
Observations of the high vibrational levels of N2(B 3Πg) in the Lewis–Rayleigh afterglow of nitrogen
Authors: Ung A. Y.-M.
Published: February 2003

Optical studies of the first positive system in the nitrogen afterglow were conducted in a conventional discharge -flow system. The vibrational level of v′=13 was observed readily at pressures up to 20 torr. For the first time, high-vibration levels of N2(B 3Πg) with v′≳13 were observed in the Lewis–Rayleigh afterglow under conditions of sufficiently high [N] and purity of N2. Bands from ΔV=4, 5, and 6 with v′ up to 26 have been identified. Based on the observed effects of pressure, temperature, atom concentration, and gas purity on the intensity of the emission bands, excitation processes responsible for the formation of these high-vibration levels are briefly discussed.
Mechanism of vibrational relaxation in molecular solids
Authors: Goodman J. , Brus L. E.
Published: February 2003

The NH and ND(A 3Π) vibrational relaxation rates, and the X 3Σ−?A 3Π spectra, have been investigated in different types of amorphous solid rare gas environments. The vibrational relaxation Hamiltonian is short range, and effectively sees only the nearest neighbors. The relaxation rates are independent of whether the local neighborhood host phonon structure is localized or delocalized. In mixed Ar+Kr hosts, NH* relaxes at the same rate with one or two nearest Kr neighbors as in pure Kr. As the number of Kr nearest neighbors increases, the guest–host interactions, controlling both spectra and relaxation, saturate and are not pairwise additive. This result is qualitatively consistent with gas phase van der Waals complex studies indicating incipient chemical bond formation. The correct local mode theoretical formulation of the solid phase relaxation problem is discussed.
Product magnetic deflection slotted disk velocity analysis molecular beams kinetics: Li+Cl2, Br2, and ICl
Authors: Sholeen Charlotte M. , Gundel Lara A. , Herm Ronald R.
Published: February 2003

An inhomogeneous deflecting magnet and slotted disk velocity analyzer combination has been used to deflect aside nonreactively scattered Li atoms and thereby measure velocity distributions of LiBr and LiCl reactively scattered from crossed thermal beams of Li and Br2 or Cl2. Transformation of these data into the center-of-mass coordinate system provides contour maps of the differential reactive cross sections which indicate that the Li+Br2 and the Li+Cl2 reactions have the following features in common: (a) The reaction mechanisms are direct; (b) The product angular distributions are broad although foward scattering is preferred (i.e., LiX scattered in the direction of the Li velocity); (c) Small product recoil energies are most probable but the product recoil energy distributions have a long tail. There is a strong coupling of the product recoil angle and energy distributions for Li+Cl2→LiCl+Cl with forward scattering favoring higher product recoil energy; however, this coupling phenomenon is weak or nonexistent for the Li+Br2→LiBr+Br reaction. Semiquantitative observations are also presented for the Li+ICl reaction. These results are discussed in relation to previous experimental and theoretical work on the reactions of alkali atoms with halogen molecules.
Three-particle collisions and termolecular reaction rates
Authors: Newton Roger G.
Published: February 2003

Quantum mechanical expressions are derived for chemical reaction rate constants in terms of collision rates for a process in which three molecules enter and three emerge.
Thermochemical properties of gaseous EuO
Authors: Murad Edmond , Hildenbrand D. L.
Published: February 2003

The dissociation energy of gaseous europium monoxide, D0° (EuO) has been measured mass spectrometrically using three independent isomolecular equilibria: Eu(g)+AlO(g) =EuO(g)+Al(g), (1) Eu(g)+BaO(g) =EuO(g)+Ba(g), (2) Eu(g)+TiO(g) =EuO(g)+Ti(g). (3) These equilibria yield D°0(EuO) =111.9±2.4 kcal/mol (or 4.85±0.10 eV), from which is derived a value of ΔHf° (EuO, g, 298.15 K) =−11.6±2.4 kcal/mol. Previous measurements of D°0(EuO) are reinterpreted and discussed in view of this work. The ionization potential of EuO was measured and found to be 6.3±0.2 eV.
Kinematic studies of electron transfer processes between alkali atoms and molecules. K+O2
Authors: Mochizuki T. , Lacmann K.
Published: February 2003

Measurements of angle and energy differential cross sections for the reaction K+O2→K++O−2 are reported for collision energies between 0.75 and 30 eV above threshold. The ionization cross section in the forward direction shows two peaks at energy losses of 4.6 and 5.1 eV. While the first peak indicates a maximum transition probability into the 4th to 6th vibrational levels of the ground state O−2[2Πg], the second peak is an indication of an excited O−2 state [4Σu or 2Πu]. With increasing deflection angle the energy loss spectrum shifts toward smaller values. At a collision energy of 14 eV, the angular differential cross section for a fixed energy loss of 5.1 eV has a maximum at a deflection angle of 7.5°; at a 4 eV energy loss, however, the peak is at 22° in the center-of-mass system, dropping off steeply at 25°, which is the rainbow angle. The deflection angle mainly depends on the Coulomb force the particles experience during the collision. For encounters leading to electronically excited O−2 the influence of this force is smaller, leading to smaller rainbow angles than for products formed in the ground state.
The local symmetry of Ce3+, Nd3+, Er3+, and Yb3+ in frozen aqueous solutions as studied by EPR and the linear electric field effect
Authors: Mims W. B. , Davis J. L.
Published: February 2003

We have found that the rare earth ions Ce3+, Nd3+, Er3+, and Yb3+ in frozen aqueous solutions, containing an additional component such as glycerol or ethanol, are coordinated noncentrosymmetrically and in a highly inhomogenous manner. For Nd3+ in a water:ethanol mixture the results can be explained on the assumption that the complexes are characterized by a point symmetry which is basically D3h as in lanthanum ethyl sulfate but the crystal field also contains a large random element. A simple electrostatic model based on the measured values of the electric field induced g shifts suggests that a random spread of ≲ 10° in the orientations of the coordinating dipoles would suffice to account for the observed inhomogeneity.
Entropy and macroscopic disequilibrium. II. The information theoretic characterization of Markovian relaxation processes
Authors: Levine R. D.
Published: February 2003

This paper considers the characterization of disequilibrium in uniform systems in terms of the time evolution of the macroscopic observables. Using these as the independent variables the procedure of maximal entropy is employed to generate a new, complementary set of independent variables, the thermodynamic forces. An equation for the time rate of change of the macroscopic observables (i.e., for the thermodynamic fluxes) which is valid also for a finite displacement from equilibrium is derived. The kinetic coefficients satisfy reciprocity relations and reduce to the Onsager coefficients in the linear regime. An equation of motion which is linear in the thermodynamic forces throughout the relaxation process is then obtained using the Legendre transform technique. The two possible equations of motion are strictly equivalent and provide (complementary) generating functions for the thermodynamic forces and fluxes. Among all possible population distributions consistent with the magnitude of the macroscopic observables, the ’’most probable’’ distribution is shown to be characterized by having the lowest rate of entropy production throughout the relaxtion process. The Rayleigh–Onsager principle of least dissipation of energy is extended to the nonlinear regime. It is then employed as a variational principle to derive the equations of motion, which inherently satisfy the reciprocity relations and which are valid throughout the relaxation process. An evolution criterion for the system is thereby provided.
Relativistic energy levels and bonding in actinide hexaflourides
Authors: Koelling D. D. , Ellis D. E. , Bartlett Rodney J.
Published: February 2003

A fully relativistic self-consistent Dirac–Slater model has been used to calculate one-electron energy levels and charge distributions for UF6, NpF6, and PuF6. Analysis of ground state charge densities reveals 5fn populations similar to free atom states; we are able to distinguish between metal–ligand bonding levels and the optically active levels described by crystal field theory. Ultraviolet and optical excitations, as well as ionziation energies, are calculated using an approximate transition state procedure and found to be in reasonable agreement with experiment. The Coulomb correlation integral appearing in the determination of the nature of 5f orbitals in solids is discussed on the basis of the systematics observed in our transition state calculations.
Molecular Rydberg transitions. V. Atomic correlation lines
Authors: Chattopadhyay S. , Hochmann P. , McGlynn S. P.
Published: February 2003

It is shown, for several groups of atoms, that the term values of low-energy Rydberg excitations are linearly correlated with the corresponding ionization potentials. The form of this relation is T (μ,α,n)/Z2=anαIμ/Z2+bnα, where T (μ,α,n) is the term value of the nth lowest-energy Rydberg state of αth type (i.e., α is a symmetry index) derived from the μth cationic parent; Iμ is the ionization potential; Z is the core charge; and anα and bnα are the correlation coefficients. A discussion of the intercepts bnα leads to the concept of an average (or zero-order) member of a given group of atoms and to determination of spectroscopic data for this ’’average atom.’’
EPR of Mn2+, Fe3+, and Cu2+ in glasses of the systems BaO–B2O3–Al2O3 and CaO–B2O3–Al2O3
Authors: Nicklin R. C. , Farach H. A. , Poole C. P.
Published: February 2003

An electron paramagnetic resonance study was made of Mn2+, Fe3+, and Cu2+ doped into the glass systems BaO–B2O3–Al2O3 and CaO–B2O3–Al2O3. The spectra of the manganese doped samples exhibited a barely resolved Mn2+ hyperfine pattern at g=2 and in some cases low field lines at g∼3 and g∼5. The concentration dependence of these low field lines is interpreted in terms of the lattice distortion produced by the very large barium and calcium ions and the resulting large zero field (D term) splitting. The 0.1% Mn samples produced better resolved hyperfine patterns than the 1% samples. The spectra of iron and copper doped glasses were also strongly concentration dependent. The results are discussed in terms of the glassy regions of the phase diagram.
Cumulant expansion of a Fokker–Planck equation: Rotational and translational motion in dense fluids
Authors: Evans Glenn T.
Published: February 2003

A frequency generalized cumulant method is applied to the rotational (R) and translational (T) Fokker–Planck equation derived by Hwang and Freed. The lowest order nonvanishing cumulant is second order in the streaming part of the Liouville operator and generates the R–T coupled Smoluchowski equation. The structure of the fourth and sixth order cumulants for uncoupled R–T motion of a spherical top allows an approximate summation of the cumulant series which is accuate for dense fluids. The orientational time correlation functions for lth rank spherical harmonics calculated using the summed cumulants are in agreement with the high density Fixman and Rider solutions to the rotational Fokker–Planck equation. The zero frequency part of the orientational correlation functions gives an improved Hubbard relation relating the orientational and angular momentum correlation times. For the translational case, the summed cumulants lead to a wave vector and frequency dependent single partice diffusion constant. The effects of R–T coupling on the single particle orientational correlation functions are calculated using the Happel and Brenner model for the hydrodynamic part of the torque–force correlation functions. The effects are concluded to be small for a Brownian particle, even if the particle has strongly coupled orientational and translational modes.
Thermodynamics of the vaporization processes for potassium sulfate
Authors: Eliezer I. , Howald R. A.
Published: February 2003

In the design of MHD systems and components it is necessary to have reliable values for the vaporization of potassium sulfate including thermodynamic values for K2SO4(g), and partly for this reason there are a number of recent experimental studies on the vapor pressure of K2SO4. This paper reviews these data critically, calculates a theoretical heat capacity curve for K2SO4(g), and replaces second law calculations with a third law treatment, obtaining ΔH°f298.15=−261.2 kcal/mol and S°298.15 90.63 eu for K2SO4(g). Thermodynamic values for K2SO4(g) are computed and tabulated for temperatures in the range from 1000 to 2200 K and are used to calculate the concentrations of various potassium containing species present in seeded combustion gases over the temperature range where liquid and solid K2SO4 may form.
Spin–echo diffusion coefficients of water to 2380 bar and −20°C
Authors: Angell C. A. , Finch E. D. , Bach P.
Published: February 2003

The self-diffusion coefficient of water has been measured by the steady-gradient spin-echo method at pressures up to 2380 bar and temperatures between 2 and −20°C in the stable liquid range using both strengthened glass and beryllium–copper pressure vessels. At low temperatures and high pressures the diffusion coefficient becomes almost independent of pressure. However, a rapid increase in DH2O with the first kilobar of applied pressure is inferred for the supercooled liquid from the relation of the new data to the 1 atm pressure diffusivity of supercooled water. The observations may be correlated with the high pressure low temperature thermodynamic properties of water in a manner consistent with the Adam–Gibbs entropy theory of liquid transport processes.
Regular chemisorption of hydrogen on graphite in the crystalline orbital NDO approximation
Authors: Dovesi Roberto , Pisani Cesare , Ricca Franco , Roetti Carla
Published: February 2003

A Hartree–Fock treatment of the regular chemisorption of hydrogen on a graphite monolayer in a crystalline orbital NOO approximation is presented. The computational problems concerning the full exploitation of the point symmetry of the lattice, as well as the integration procedures are the same as encountered in a corresponding ab initio treatment. Three different cases have been considered, corresponding to the chemisorption of one hydrogen atom per unit cell: (A) above alternate carbon atoms; (B) above the center of a C–C bond; (C) at the center of a carbon ring. Bound states are found to occur only for cases A and B. The electronic features of the adsorbent–adsorbate system are appreciably differentiated. Such differences are discussed by using energy band structures and total and partial density of states spectra.
Role of the 4f55d band in the radiationless 5D1→5D coupling in BaCl2:Sm2+ and BaBr2:Sm2+
Authors: Lauer H. V. , Fong F. K.
Published: February 2003

In this paper, the adiabatic relaxation theory is applied to investigate the origin of rare-earth fluorescence quenching involving multiphonon transitions. The energy level schemes for BaCl2:Sm2+ and BaBr2:Sm2+ have been obtained from the observed fluorescence spectra. The phonon cutoff frequencies, 210 and 140 cm−1 for BaCl2 and BaBr2, respectively, have been determined from vibronic sidebands. From the observed temperature dependence of the fluorescence intensities and lifetimes, it is shown that the 5D1 and 5D0 levels are thermally quenched through radiationless excitation to the 4f55d band and that the population of the 5D0 level from 5D1 involves the 4f55d band as an intermediary. This indirect f (→d) →f relaxation mechanism appears to have resulted from the proximity and relatively large displacement between the adiabatical surfaces of the low-lying 4f55d and the 5D1 states of Sm2+ in BaCl2 and BaBr2.
CO(d 3Δi→X 1Σ+) fluorescence from photodissociation of CO2 by 923 Å photons
Authors: Phillips E. , Lee L. C. , Judge D. L.
Published: February 2003

CO(d 3Δi→X 1Σ+) fluorescence has been observed from photodissociation of CO2. A NIV line emission source at 923.2 Å provided the primary photons. The absolute cross section for production of the CO(d→X) fluorescence was found to be 0.49±0.25 Mb. Relative band intensities for the dv=3→X bands have been obtained which indicate that the electronic transition moment has a parabolic dependence on the r centroid. Branching ratios for d→X to d→a are estimated to be 0.076 for transitions from dv=3 and 0.021 from dv=2. No dv=1→X fluorescence was observed.
Molecular motions in liquid. I. Rotation of water and small alcohols studied by deuteron relaxation
Authors: Fung B. M. , McGaughy Tim W.
Published: February 2003

The deuteron spin lattice relaxation time T1 of CH3OD, C2H5OD, (CH3)2CHOD, and (CH3)3CHOD is reported as a function of temperature and frequency. The deuteron T1 of the alcohols in dilute benzene solutions was also measured at 25°C. A detailed analysis of the experimental results and other magnetic and dielectric relaxation data from the literature was made. Based upon the analysis, it is suggested that the success of the Debye model in explaining the dielectric and magnetic relation behavior of water and small alcohols may be purely coincidental. It seems that the error in applying Stokes law for the rotation of a macroscopic sphere to small molecules in liquid and the error in assuming that water and alcohols rotate as monomers largely cancel each other, yielding much better apparent agreement between calculated and experimental data than those for nonassociating liquids. The deuteron T1’s for the alcohols are further analyzed in terms of anisotropic rotation.
Attachment of slow electrons to hexafluorobenzene
Authors: Gant K. S. , Christophorou L. G.
Published: February 2003

Slow (≲ 3 eV) electrons attach to hexafluorobenzene (C6F6) nondissociatively with large cross sections via two distinct processes, one at ∼0.0 eV and another peaking at 0.73 eV. The absolute rates and cross sections have been determined as a function of electron energy for both processes and are reported. At 0.03 and 0.73 eV the cross sections are 1.23×10−14 and 8.04×10−16 cm2, respectively; the thermal (T=297°K) value of the attachment rate is 3.3×109 sec−1 torr−1(=1.02×10−7 sec−1 molecule−1 cm3). The lifetime τ of C6F6−* at ∼0.0 eV is ∼12 μsec, but at 0.73 eV it is much shorter, 10−8≲τ<10−6 sec. The ∼0.0 eV process is associated with electron capture into the degenerate π4 and π5 molecular orbitals and is ascribed to the configurations π21π22π23π14 and π21π22π23π15, while the 0.73 eV process is associated with electron capture into the π6 orbital and is ascribed to the configuration π21π22π23π16. For both C6H6 and C6F6 a relationship is shown to exist between the ionization energies of the occupied π1 and π2, π3 orbitals and the position of the negative ion (shape) resonances associated with the unoccupied π4, π5, and π6 orbitals. The observed large attachment rates for C6F6 extending from thermal energies to ≳3 eV recommend it as a potential ’’additive’’ in high-voltage multicomponent gaseous insulators.
Density dependence of the ratio of second to first order terms in a perturbation expansion of characteristic thermodynamic properties of dense noble gases
Authors: Clippe Paulette
Published: February 2003

The perturbation theory is applied to the evaluation of the thermodynamic properties of dense noble gases. The numerical results obtained for the ratio of the second to the first order perturbation terms as a function of the density are compared to those proposed by Rosenfeld and Thieberger for model gases, like the square-well and the triangular-well potential gases. These authors have remarked that for a given potential range the ratio decreases for increasing density and that this ratio is smaller for the compressibility than for the free energy. They have also pointed out that such ratios increase for a shorter square-well range. It is shown here that such observations cannot be directly extended to more complicated systems like argon and xenon. The difference obviously stems from the long range attractive tail and the softness of the core of the intermolecular potential for such systems.
The transport coefficients for a fluid of square-well rough spheres: Comparison with methane
Authors: Scarfe K. D. , McLaughlin I. L. , Collings A. F.
Published: February 2003

Recently derived expressions for the transport coefficients of a dense fluid of square-well rough spheres and corresponding expressions for smooth spheres have been evaluated with structural data generated in computer simulations. The results are used with recommended square-well potential parameters to calculate the tranport properties of methane for both models. For the shear viscosity and thermal conductivity the rough-sphere values have the better agreement with experiment, while for the self-diffusion coefficient they have marginally the worse agreement. No experimental data exist with which to compare the calculated bulk viscosities, which are considerably higher for rough than for smooth spheres.
Closed form of second virial coefficient for Mie m–n potential
Authors: Ley-Koo E. , de Llano M.
Published: February 2003

It is shown that the second virial coefficient for the Mie m–n potential can be expressed in closed form involving a limited number of generalized hypergeometric functions, when the ratio m/n is a rational number.
The thallium mercury excimer and its potential as a laser
Authors: Drummond D. , Schlie L. A
Published: February 2003

Normalized fluorescence measurements of the thallium mercury band emission at 4590 and 6560 Å show that these bands have great promise for excimer laser action. The use of mercury as a broadening gas results in potential wells approximately four times as deep as those of the corresponding thallium xenon states. This effect, which is probably due to mercury’s high polarizability, leads to excimer band emission which is about a factor of 100 times more intense than that for thallium xenon at a given perturber gas density. Using the density dependence of the molecular fluorescence intensity, the molecular formation rate constant of the thallium mercury B 2Σ1/2 well is estimated to be 2.0×10−31 cm6/sec. It appears that the ideal laser operating conditions should be about 1019 Hg/cm3, 1016 Tl/cm3, and 6×1019 He or Ar/cm3. Under these conditions, at 720°C, an excited state Tl density of 3×1014/cm3 will result in a stimulated emission coefficient of about 1% per centimeter at either 4590 or 6560 Å. If successful, this laser will be most appropriate for high average power, rather than high peak power, because of the limitations imposed on the peak power by the molecular formation and thermalization rates. Tests of low power arc discharge in thallium iodide and mercury show that the kinetics and spectra of the excimer are apparently unaffected by the substitution of the salt for the pure metal. The use of such salts could lower the required operating temperature to around 350°C.
A variational approach to the theory of ionic solutions
Authors: Olivares W. , McQuarrie D. A.
Published: February 2003

In this paper we discuss a known variational principle for the Percus–Yevick integral equation and then generalize the procedure to obtain a variational principle for any integral equation associated with the Ornstein–Zernike equation. In particular we rederive a variational principle for the mean spherical model and then derive a variational principle for the hypernetted chain equation and compare these to the exact numerical results of Rasaiah and Friedman and to the Monte Carlo data of Rasaiah, Card, and Valleau for the restricted primitive model of electrolyte solutions.
Calculations of molecular ionization energies using a self-consistent-charge Hartree–Fock–Slater method
Authors: Rosén A. , Ellis D. E. , Adachi H. , Averill F. W.
Published: February 2003

A numerical-variational method for performing self-consistent molecular calculations in the Hartree–Fock–Slater (HFS) model is presented. The molecular wavefunctions are expanded in terms of basis sets constructed from numerical HFS solutions of selected one-center atomlike problems. The binding energies and wavefunctions for the molecules are generated using a discrete variational method for a given molecular potential. In the self-consistent-charge (SCC) approximation to the complete self-consistent-field (SCF) method the results of a Mulliken population analysis of the molecular eigenfunctions are used in each iteration to produce ’’atomic’’ occupation numbers. The simplest SCC potential is then obtained from overlapping spherical atomlike charge distributions. The molecular ionization energies are calculated using the transition-state procedure; results are given for CO, H2O, H2S, AlCl, InCl, and the Ni5O surface complex. The agreement between experimental and theoretical ionization energies for the free-molecule valence levels is generally within 1 eV. The simple SCC procedure gives a reasonably good approximation to the molecular potential, as shown by comparison with experiment, and with complete SCF calculations of Baerends et al. on CO, H2O, and H2S.
Raman spectroscopy of protein–water interactions in aqueous solutions
Authors: Cavatorta Fabrizio , Fontana Marco P. , Vecli Arnaldo
Published: February 2003

Some conclusions about the effect of protein presence on water structure, as found by Raman spectroscopy, are presented here. An overall intensity decrease and strong spectral shape changes which are encountered in the OH stretching region when increasing protein concentration are explained in terms of a water model taking into account three water species with different Raman efficiency. The hydration value of protein is calculated and results are an order of magnitude greater than those previously reported. A simple model of protein water interaction is formulated to explain the presence of a quasitransition point in OH stretching intensity when varying concentrations. Correlation is made with calorimetric data.
Complex formation in the C+(2P)+CH4 reaction at 0.1 to 10 eV
Authors: Smith Richard D. , DeCorpo James J. , Allen William N. , Lampe F. W.
Published: February 2003

Product distributions are reported for the C+(2P)+CH4 reaction between 0.1 and 10 eV. Upper limits to the fraction of the total reaction involving an excited ethylene ion intermediate are estimated by comparison of product distributions with breakdown curves for ethylene ions. The results indicate a decrease in complex formation at higher translational energies and suggest more direct mechanisms contribute to C2H2 + and C2H3 + formation at higher energies.
Chemiluminescent reactions of Al atoms and halogens
Authors: Rosenwaks S.
Published: February 2003

Al atoms diluted in a buffer gas were reacted with F2, Cl2, Br2, I2, NF3, and SF6 producing chemiluminescent flames. Emission from the a 3Π to the ground X 1Σ+ state of AlX(X=F, Cl, Br, I) and from higher electronic states of AlF and AlCl has been observed. Bands of NF and N2 were emitted from Al+NF3 reaction. Al lines were observed from all reaction mixtures except Al+I2, and it is suggested that Al atoms are excited by energy transfer from metastable molecules formed in the reactions. Photon yields were 2% for Al+NF3 and less than 0.01% for Al+F2, Cl2, Br2, I2, and SF6.
On the dimensionality dependence of the properties of reactive collisions
Authors: White J. M.
Published: February 2003

Quasiclassical trajectory calculations have been carried out in 1D, 2D, and 3D on potential energy surfaces modeling H+Br2 and H+HBr collisions with the reactants in the ground vibration–rotation state. Cross sections, reaction lengths, and reaction probabilities are reported as a function of relative translational energy. Using information theoretic concepts, the surprisal of the branching ratio Γ=ka/ke for the processes H+HBr→H2+Br (ka) and H′+HBr→H′Br+H(ke) is studied in all three dimensions. The surprisal in 1D has a much different energy dependence than in 3D while the 2D surprisal follows the 3D surprisal more closely. The surprisals of the above two reactions and the H+Br2→HBr+Br reaction are reported as a function of energy. While the surprisals all show the same qualitative energy dependence the 1D results generally increase much more rapidly with energy than do the 2D or 3D. Two methods for estimating the energy dependence of 3D reaction cross sections from 2D reaction lengths or 1D reaction probabilities are compared. The method which assumes the surprisal of the reaction probability is dimensionally invariant is shown to be preferable. Given that a reaction has occurred, the distributions of scattering angles, translational energy fractions, and reactive impact parameters are compared in various dimensionalities. From all of the results taken together, it is concluded that quite reasonable (in some cases quantitative) 3D estimates of reaction properties can be derived from 2D trajectory data and information theoretic concepts. Extrapolation from 1D to 3D is shown to be of generally marginal utility.
Numerical calculation of one-electron properties from SCF–Xα–SW wavefunctions for LiH
Authors: Woodruff Susan Beatty , Wolfsberg Max
Published: February 2003

One-electron properties of LiH, including the dipole and quadrupole moments, are calculated with SCF–Xα–SW wavefunctions. The effect of the parameters of the SCF–Xα–SW method on the results has been studied. Use is made of numerical quadrature with diophantine points in the evaluation of integrals. The results are compared with those obtained with standard Hartree–Fock and configuration interaction calculations for LiH, and semiquantitative agreement is found.