bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermolecular coupling in HOD solutions
Authors: Wiafe-Akenten J. , Bansil R.
Published: February 2003

Intermolecular coupling of OD oscillators from HOD in H2O has been investigated by Raman spectroscopy. The data indicate that at concentrations of HOD greater than 10 mol % the effects of intermolecular coupling of OD ⋅⋅⋅ OD pairs become noticeable. Difference spectra show a characteristic derivativelike feature with an increase of intensity around 2400 cm−1 as intermolecular coupling increases. The peak frequency of the OD stretching vibration in HOD decreases from 2525 cm−1 at infinite dilution to 2500 cm−1 in 50 mol % HOD, while the width of the OD stretching band increases from 150 cm−1 (infinite dilution) to 178 cm−1 (50 mol % HOD). Depolarization measurement indicates that the band at ∼2500 cm−1 is polarized. By comparing these difference spectra with the spectrum of OD oscillators from D2O we suggest that the major features of the D2O spectrum in the liquid state can be obtained by considering intermolecular coupling of OD oscillators.
Infrared gas phase intensity measurements, polar tensors, and effective charges of cis-difluoroethylene and its deuterated modifications
Authors: Kagel R. O. , Powell D. L. , Overend John , Ramos Mozart N. , Bassi A. B. M. S. , Bruns Roy E.
Published: February 2003

All gas phase fundamental vibrational intensities for cis-difluoroethylene and its deuterated modifications have been measured. Isotopic invariance, G sum rule, and quantum chemical information have been used in selecting preferred experimental values for the dipole moment derivatives and polar tensor elements of cis-C2H2F2 and C2D2F2. The G sum rule has been used to determine individual intensity values for the ν11, ν12, overlapped band system of the dihydrogen molecule. Values of the polar tensor elements for cis-difluoroethylene are compared with those found previously for vinylidene fluorine. The hydrogen effective charge value of 0.17 e of cis-difluoroethylene is much smaller than the value of 0.29 e for vinylidene fluoride. The polar tensor of cis-difluoroethylene is shown to provide an excellent estimate of the vibrational intensities of trans-difluoroethylene.
Effect of anion substitution on the electron spin resonance of Cr5+ in calcium phosphate apatite
Authors: Pifer J. H. , Ziemski S. , Greenblatt M.
Published: February 2003

Electron spin resonance studies have been made at 4.2 K of CrO3−4 substituted for PO3−4 in three calcium phosphate apatites. The hydroxyapatite studied has a hexagonal structure stabilized by Cl− impurities. The fluorapatite is confirmed by the ESR to undergo a phase transition involving small structural changes to a noncentrosymmetric phase. But the ESR shows that the distortion of the PO3−4 tetrahedra is remarkably similar to that of the hydroxyapatite. Chlorapatite has a centrosymmetric monoclinic structure and has a considerably more distorted PO3−4 tetrahedron. Comparison of the results with previously studied hexagonal barium and strontium apatites shows that cation substitution has a much stronger effect on the PO3−4 structure than does anion substitution.
Electronic reorganization in the photoelectron spectra of transition metal compounds
Authors: Böhm Michael C.
Published: February 2003

The validity of Koopmans’ theorem in a series of 16 transition metal compounds with a large variety of 3d centers (Ti, Cr, Mn, Fe, Co, Ni, and Zn) is investigated. The reorganization energies are determined by means of the Green’s function method employed in a semiempirical INDO Hamiltonian. A self-energy approximation is used that allows a fragmentation of the calculated Koopmans’ defects into relaxation increments as well as into correlation parameters that take into account the loss of pair correlation in the electronic ground state and the modification of the pair correlation in the cationic hole state. The magnitude and the importance of these parameters are studied as a function of the 3d occupation pattern, the oxidation state of the transition metal center, the nature of the orbital wave functions and the one-particle energies. It is demonstrated that pair relaxation energies in the various hole states are by no means negligible in comparison to the relaxational corrections that lead to the most pronounced deviations from IKv,j (IKv,j=− εj). The limitations of purely relaxational models (e.g., ΔSCF approach) are analyzed in detail. The gradual modifications of the calculated Koopman’s defects within the 3d series are rationalized. The most pronounced reorganization energies are encountered in d6–d8 complexes. The magnitude of relaxation and correlation is reduced with a decreasing and an increasing number of 3d electrons. The physical background leading to the breakdown of Koopman’s theorem in 3d derivatives is compared with the results of recent studies in various molecular species (e.g., small molecules, organic lone-pair systems).
ESR and ENDOR study of photoexcited triplets of cyano-substituted porphyrins
Authors: van Willigen Hans , Chandrashekar T. K.
Published: February 2003

An ENDOR study has been made of the photoexcited triplets of some cyano-substituted zinc tetraphenylporphyrins randomly oriented in a rigid matrix. The results demonstrate that the ENDOR method can be applied in studies of short-lived triplets (triplet lifetime < 1 ms) in amorphous solids. The application is possible because of the fact that the ESR signal intensity is strongly enhanced by electron spin alignment. As a consequence of the spin alignment, ENDOR spectra can appear in absorption or emission depending on the field setting employed. Hyperfine data derived from the spectra reflect the effect of CN substitution on the electron spin distribution.
Rotational energy transfer in HF
Authors: Wilkins Roger L. , Kwok Munson A.
Published: February 2003

A rotational nonequilibrium model has been developed to simulate the infrared double-resonance experimental technique designed to study rotational relaxation of HF gas in the v=1 and higher vibrational states. State-to-state rate coefficients for this rotation-to-translation relaxation model have been obtained from a surprisal analysis and are found to scale as an inverse power of the rotational energy transferred. Phenomenological rates for the rotational energy transfer in the v=1 state for J=0 to J=7 with Δ J =+1, +2, +3, and +4 are found to be in excellent agreement with the reported phenomenological rates from available experiments for both the v=1 and v=2 states. It appears, therefore, that the state-to-state rate coefficients for rotational relaxation of HF are insensitive to the v state. Angular momentum statistics corresponding to conservation of mj are found to give better fits to the data than those with mj assumed to be completely randomized.
Intermolecular multiple scattering of electrons. II. Observed effects for SF6
Authors: Jin Anding , Bartell Lawrence S.
Published: February 2003

A theory of intermolecular multiple scattering of electrons by vapor molecules is tested by comparing predicted effects with effects observed over a wide range of sample densities. It is found that the theory, which contains no adjustable constants and is based on small angle approximations, gives a good account of experimental observations. The degree to which experimental structure refinements are degraded by multiple scattering is also examined. It is found that derived internuclear distances are disturbed very little even when the mean number of scatterings per electron is as high as 2 and the interference features are washed out by a factor of 2. Apparent amplitudes of vibration are influenced more significantly but are still correctable with fair precision.
Diffusional instabilities in a layered oscillating medium
Authors: Bewersdorff Axel B.
Published: February 2003

The evolution of an oscillatory reagent with an imposed gradient of periodicity is studied by experiment and by computer simulation. It is found that the initial system of regular phase waves evolves into an irregular distribution of propagating structures. The local transition to second generation waves is abrupt and exhibits a remarkable sensitivity to weak inhomogeneities of the substrate. The results support the view that generation of chemical chaos is favored by diffusion.
Raman-active torsional vibrations in DNA molecule
Authors: Tsuboi Masamichi , Tominaga Yasunori , Urabe Hisako
Published: February 2003

Raman active torsional frequencies are calculated using the elastic constants of mitter et al..1 (AIP)
A prediction of the rotational states for partially deuterated ammonium ions in NH4−xDxClO4
Authors: Maki Kazuo
Published: February 2003

Splittings of the librational ground state of partially deuterated ammonium ions in the ammonium perchlorate crystal are calculated. Heat capacity anomalies are predicted to be observed at around 1–3 K, a careful measurement of which will be very useful for characterizing the anisotropy of the rotational potential.
A fluorescence system of matrix-isolated PbBi
Authors: Epting Michael A. , Nixon Eugene R.
Published: February 2003

A fluorescence band system in the yellow is reported. This system is attributed to the mixed diatomic PbBi isolated in both solid Ar and Ne. (AIP)
A study of the dynamics of UV laser photolysis of NOCl and NOBr
Authors: Moser Mark D. , Weitz Eric , Schatz George C.
Published: February 2003

The photodissociation of NOCl and NOBr using lasers operating at 193 (ArF), 249 (KrF), 308 (XeCl), and 337 nm(N2) has been studied under collisionless conditions by measuring the infrared fluorescence of the NO product. Little difference between the results for NOBr and NOCl was observed and all results indicate a linear dependence of photodissociation yield on laser power. The extent of NO vibrational excitation observed was quite large in photodissociation utilizing the ArF and KrF laser lines, with states up to v≥16 observed with ArF and up to v≥14 with KrF. The XeCl and N2 lines produced much less NO excitation, up to v≥5. Statistical, half-collision, and Franck–Condon models of the photodissociation dynamics were studied, with best agreement with experiment for dissociation at 193 and 249 nm being obtained using a Franck–Condon model. An excited potential function for NOCl in which the NO properties were taken to be close to that of NO(4Π) was found to predict the shape of the dissociated NO vibrational distribution accurately at both 193 and 249 nm. Photolysis at 308 and 337 nm could also be explained by a Franck–Condon model using the NO(A2Π) state to model the NOCl excited state.
Vibration-to-vibration energy transfer in the deexcitation of HCl(v) by HCl(0): Role of the rotational and translational motions
Authors: Shin H. K.
Published: February 2003

The deexcitation of HCl(v) by HCl(0) for v=1–4 is shown to undergo vibration-to-vibration (V–V) energy exchange with the transfer of the energy mismatch ΔE through rotation (R) and translation (T). When v is small, the translational motion plays a major role in transferring ΔE, but when v is large, the rotational motion is of major importance in supplying ΔE. The sum of V–V, T and V–V, R contributions are in reasonable agreement with observed data at 300 K. For v≳4, the V–V mechanism appears to underestimate deexcitation probabilities seriously.
The weakly exothermic rearrangement of methoxy radical (CH3O⋅) to the hydroxymethyl radical (CH2OH⋅)
Authors: Saebo/ Svein , Radom Leo , Schaefer Henry F.
Published: February 2003

Although the CH3O⋅ and CH2OH⋅ radicals have long been considered critical intermediates in combustion and atmospheric processes, only very recently has the potential significance of the isomerization CH3O⋅→CH2OH⋅ been appreciated. This isomerization and related aspects of the CH3O⋅/CH2OH⋅ potential surface have been studied here using nonempirical molecular electronic structure theory with moderately large basis sets and with incorporation of electron correlation. The vibrational frequencies of CH3O⋅, CH2OH⋅ and seven other stationary points on the potential energy hypersurface have been predicted, both to compare with results from spectroscopy and to provide estimates of zero-point vibrational corrections. In general, there is reasonable agreement with those vibrational frequencies of CH3O⋅ and CH2OH⋅ which are known from experiment. Our ab initio calculations predict that CH3O⋅ lies 5.0 kcal mol−1 higher in energy than CH2OH⋅ with a barrier to rearrangement to CH2OH⋅ of 36.0 kcal mol−1. Rearrangement of CH3O⋅ to CH2OH⋅ via a dissociation–recombination mechanism is energetically more costly (by 6.1 kcal mol−1). The Jahn–Teller distortion of CH3O⋅ from point group C3v is described in some detail. Barriers to inversion and rotation in CH2OH⋅ are predicted and compared with the results of ESR experiments. Finally, the dissociation of CH3O⋅ and CH2OH⋅ to yield formaldehyde plus H⋅ are each predicted to involve modest reverse activation energies.
A non-mass-dependent isotope effect in the production of ozone from molecular oxygen
Authors: Heidenreich John E. , Thiemens Mark H.
Published: February 2003

Experimental demonstration of a new, non-mass-dependent isotopic fractionation process is presented. The effect is analytically demonstrated by mass spectrometric analysis of 16O, 17O, and 18O distributions in the reactants and products in the electrosynthesis of ozone from molecular oxygen. The effect appears to be a result of differences in reaction kinetics as a result of symmetries of the isotopically substituted molecules. The direction, magnitude, and abundance distribution of the oxygen isotopes has a direct bearing on theories for the evolution of the solar system.
Diffusion in concentrated hard sphere dispersions: Effects of two and three particle mobilities
Authors: van Megen W. , Snook I. , Pusey P. N.
Published: February 2003

Using the Verlet–Weis hard sphere radial distribution functions and the Monte Carlo method we calculate the short time self- and mutual-diffusion constants for a hard sphere dispersion at volume fractions up the disorder/order transition. The computations are based on two and three particle mobility tensors. The results show that the two particle mobility tensor alone is completely inadequate at high particle concentrations and considerable improvement is obtained when three particle interactions are included.
Short time structural relaxation processes in liquids: Comparison of experimental and computer simulation glass transitions on picosecond time scales
Authors: Angell C. A. , Torell L. M.
Published: February 2003

Recent Brillouin scattering studies of relaxation in the simple ion system Ca++–K+/NO−3 (two particles of argon structure and a small anion) provide the experimental basis for a direct comparison of glass transformation phenomenology in computer simulated LJ argon ‘‘glass,’’ with that in laboratory substances studied on the same time scale. Most of the attenuated glass transition characteristics observed for LJ argon are found in the ionic system, and the same relation of the dispersion midpoint to the so-called ‘‘ideal’’ glass transition temperature is observed. Analysis of the real and imaginary parts of the complex longitudinal modulus shows that at high temperatures the relaxation function for Ca++–K+–NO−3, in strong contrast with that at normal low temperature behavior, closely approaches a simple exponential decay with Arrhenius form for the relaxation time. Furthermore, the high temperature Arrhenius plot extrapolates naturally to the reciprocal quasilattice vibration frequency determined by far infrared absorption studies on the glassy solid. Because of the low activation energy in the high temperature regime the glass ‘‘transition’’ observed with decreasing temperature is smeared out almost beyond recognition. It is argued that this will be a rather general phenomenon for hyperquenched glasses and that for such cases, the fictive temperature concept which associates the glass structure with an internally equilibrated liquid structure (that at Tfictive) must collapse. Parallels between LJ argon and Ca+–K+–NO3–glasses are discussed.
Carbon monoxide oxidation on the Pt(111) surface: Temperature programmed reaction of coadsorbed atomic oxygen and carbon monoxide
Authors: Gland John L. , Kollin Edward B.
Published: February 2003

Carbon dioxide formation from coadsorbed atomic oxygen and molecular carbon monoxide has been characterized using temperature programmed reaction spectroscopy over a wide range of initial oxygen and carbon monoxide coverages. The experiments were performed in an apparatus containing Auger electron spectroscopy, low energy electron diffraction, and a multiplexed mass spectrometer for the temperature programmed reaction experiments. A single reaction limited CO2 peak is observed in the 320–340 K temperature range over a wide range of initial atomic oxygen and molecular CO coverages, suggesting that a single reaction mechanism dominates. The activation energy for CO2 formation ranges from 166 kJ/mol (40 kcal/mol) for small surface concentrations of reactive adsorbed atomic oxygen and CO (0.4×1014/cm2) to 68 kJ/mol (17 kcal/mol) for larger surface concentrations of reactive adsorbed atomic oxygen and CO (2.5×1014/cm2). Low energy electron diffraction results indicate that adsorbed atomic oxygen forms islands for surface concentrations greater than about 0.4×1014 atoms/cm2 (0.10 θmax) and suggests that CO forms CO islands when CO is adsorbed on surfaces containing adsorbed atomic oxygen. The observation that this reaction does not go to completion during a temperature programmed reaction cycle indicates that the island structure of the reactants limits their availability for reaction. Apparently, the reaction proceeds by diffusion of adsorbed CO to the perimeters of the immobile adsorbed atomic oxygen islands. Similar effects have been observed previously during temperature programmed reaction and titration studies of the hydrogen–oxygen reaction on the Pt (111) surface {J. L. Gland, G. B. Fisher, and E. B. Kollin [J. Catal. 77, 263(1982)]}.
Laser optogalvanic photodetachment spectroscopy: A new technique for studying photodetachment thresholds with application to I−
Authors: Webster Christopher R. , McDermid I. Stuart , Rettner Charles T.
Published: February 2003

Electron photodetachment from I− ions has been observed using an optogalvanic technique in which an electrical discharge in iodine vapor was probed with a pulsed dye laser. The first photodetachment threshold, corresponding to the onset of production of I(2P3/2) atoms, was located at 405.18±0.02 nm giving for the electron affinity Ea(I) =3.0591±0.0001 eV.
Regularities in the resonance Raman overtone spectrum from the third excited state of chrysene
Authors: Peticolas Warner L. , Chinsky Laurent , Turpin Pierre-Yves , Laigle Alain
Published: February 2003

The frequency doubled 514 nm line of the argon laser at 257 nm is shown to fall exactly in the 0–1 absorption band of the third electronic absorption band of chrysene. Resonant Raman scattering from this vibronic state shows three strong Raman bands in the fundamental region (900–1700 cm−1) as well as bands in the overtone and combination region (2500–5000 cm−1). Only the fundamental at 1384 cm−1 shows overtone bands and it also shows combination bands with the other two. The intensity of all of the Raman bands as well as the absorption spectrum is calculated from vibronic theory on the assumption that one band (1384 cm−1) is greatly displaced in the excited state and the large Franck–Condon factors from this band helps to enhance the intensity of the other two bands which are only slightly displaced. Since the third electronic state wave function has a single node which divides the long axis of the molecule, it is suggested that the 1384 cm −1 vibration also has a single node and thus the vibration is a longitudinal stretching of the chrysene molecule.
The correlation of hydrogen diffusion with the relative concentrations of cubic and axial Fe3+ sites in KTaO3
Authors: Gonzalez R. , Abraham M. M. , Boatner L. A. , Chen Y.
Published: February 2003

Hydrogen in the form of OH− ions has been incorporated into Fe-doped KTaO3 single crystals by heat treatments in H2O vapor, air, and hydrogen gas. Heat treatments in argon and oxygen resulted in a removal of OH− from the crystal. The conditions resulting in the incorporation of OH− also produced a decrease in the intensity of an axial Fe3+ EPR signal relative to the cubic site iron spectrum while the removal of OH− was accompanied by a relative increase in the axial EPR signal. The removal of oxygen from Fe-doped KTaO3 by heat treatments in potassium metal vapor was also found to elminate the axial Fe3+ EPR spectrum. These results do not support the previously accepted oxygen vacancy model for the Fe3+ axial site configuration and are contrary to the results of similar investigations of Fe3+ in SrTiO3.
A symmetry property of van der Waals like equations of state
Authors: Mistura L.
Published: February 2003

It is shown that the locus of inflection points of the isothermal curves of any equation of state having the functional form in Eq. (1) has a remarkable symmetry property in agreement with the behavior of real fluids. (AIP)
Resonance energy transfer, motional narrowing, and vibrational dephasing in molecular crystals: 390 cm−1 internal vibration of naphthalene
Authors: Hess Larry A. , Prasad Paras N.
Published: February 2003

For the naphthalene-h8 crystal, the vibrational dephasing of the 390 cm−1 Raman active vibration is investigated by the temperature dependence of the linewidth and the line shape in the Raman spectra. This mode shows a relatively large resonance transfer interaction with a consequent factor group splitting of ∼5.5 cm−1. The corresponding transition in the isotopic mixed crystal, composed of 10% naphthalene-h8 and 90% naphthalene-d8, is, predominantly, due to the monomer. This monomer transition exhibits a Gaussian line shape at 4 K and has a width of ∼1.5 cm−1. In the neat naphthalene-h8 crystal at 4 K, the line shape of the higher energy Davydov component is found to be a motionally narrowed Lorentzian with a width much smaller than that of the monomer transition in the isotopic mixed crystal. In contrast to this, the line shape of the lower energy Davydov component is asymmetric. The low energy side of the lower Davydov component is found to obey the Urbach rule, while its high energy side is a Lorentzian. Furthermore, the width of the lower Davydov component is larger than that of the upper Davydov component but still smaller than what is observed for the corresponding monomer transition in the isotopic mixed crystal. This result suggests that the vibrational exciton band k-scattering mechanism, which involves the exciton–phonon scattering, does not contribute significantly to the vibrational dephasing. It is because such a mechanism predicts that at 4 K the upper Davydov component would be broader than the lower Davydov component as observed for the electronic excitons in molecular crystals. A detailed study of temperature dependence of the linewidth of the upper Davydov component also supports the assumption that the k scattering within the vibrational exciton band is not the main contributor to the dephasing of the 390 cm−1 vibration. This observed temperature dependence of the linewidth is found to be consistent with the mechanism of pure dephasing which involves an off-diagonal quartic anharmonic interaction with the high-frequency in-plane librational phonon motions.
Chaperone participation in three body ion association reactions. The systems COH++CO=(CO)2H+ and N2H++N2=(N2)2H+
Authors: Blades A. T. , Kebarle P.
Published: February 2003

In an earlier study of the reactions (1) COH++CO+H2=(CO)2H++H2 and (2) N2H++N2+H2=(N2)2H++H2 it was observed that (1) was much faster than (2). On theoretical grounds the reactions are expected to have similar rates. A closer investigation of the reactions reveals that over a wide temperature and concentration range the products (CO)2H+ [respectively, (N2)H+] are not formed by the normal three body reaction but by a parallel sequence (the chaperone sequence), i.e., COH++2H2=COH3++H2 followed by COH3++CO=(CO)2H++H2 for the COH+ case. Significantly, for a wide range of conditions the chaperone complex COH3+ (respectively, N2H3+) is at too low concentrations to be detected, and the rate law is the same as that for the direct three body reactions. Unraveling the kinetics of the reactions led to determination of the rate constants for the direct and chaperone reactions.
New measurements of the ion content of evaporation-humidified air: Comment
Authors: Carlon Hugh R.
Published: February 2003

In a recent paper, the author indicated that a set of four different-sized vapor electrical conductivity cells of a new design was being fabricated to permit simultaneous measurements of the ion content of moist atmospheric air that would resolve the insulator leakage and vapor ion components of conductivity with greater precision. This new set of cells has been completed, and measurments have produced data which are different in some respects from those reported earlier. This paper reports the new data, and compares them with previous data.
Comment: Strict Lindemann behavior as a limiting form
Authors: Vatsya S. R. , Pritchard H. O.
Published: February 2003

The master equation formulation for a thermal unimolecular reaction is extended to a global form. Deviations from strict Lindemann behavior are discussed.(AIP).
Classical analysis of collinear light atom transfer reactions
Authors: Pollak Eli
Published: February 2003

A classical direct reaction theory is formulated and shown to account for the recently observed quantal oscillations in the reaction probability of light atom transfer reactions. Quasiperiodic orbits and irregular orbits are found for the systems although the potential energy surfaces used have only saddle points in the interaction region. These orbits imply the existence of a new type of bound species—an adiabatic molecule.
Vapor pressures and lattice energies of oxalic acid, mesotartaric acid, phloroglucinol, myoinositol, and their hydrates
Authors: de Wit H. G. M. , Bouwstra J. A. , Blok J. G. , de Kruif C. G.
Published: February 2003

In the present investigation, we report the enthalpy of dehydration and the enthalpy of sublimation of a number of organic hydrates and their anhydrous counterparts. These values are used to test the transferability of a set of atom–atom potential parameters, originally derived for carboxylic acids. The calculations showed that the parameter set was transferable to a fairly good degree.
On the density anomaly in sulfur at the polymerization transition
Authors: Kennedy Stephen J. , Wheeler John C.
Published: February 2003

We show that the density anomaly in sulfur near the polymerization transition observed by Borst and co-workers can be explained, at least in part, as a manifestation of nonclassical critical behavior. We combine the lattice solution model recently proposed to study equilibrium polymerization in sulfur with a phenomenological assumption to produce a dramatic improvement over earlier theories. Some discrepancies between the theory and experiment remain.
Motional freedom of the central metal atom in apohemoglobin reconstituted with 111In: protoporphyrin IX. Time-differential perturbed gamma-ray angular correlations
Authors: Marshall Alan G. , Lee Kai Mon , Martin Peter W.
Published: February 2003

Based on time-differential perturbed gamma–gamma angular correlations (PAC), the rotational correlation time for indium-111 in apohemoglobin reconstituted with 111In:protoporphyrin IX is τrot(Hb)=23 ns. For 111In:mesoprotoporphyrin IX reconstituted similarly into apomyoglobin, PAC measurements yield τrot(Mb)=16 ns. The PAC ratio τrot(Hb)/τrot(Mb)=1.4 is the same (within experimental error) as that from fluorescence polarization (FP) measurements for apo-Hb and apo-Mb reconstituted with an aminonaphthalene sulfonate in place of the natural heme. Since the rigid-sphere ratio τrot(Hb)/τrot (Mb)=4.0 is larger than the experimental PAC and FP ratios, the metalloporphyrin exhibits significantly more internal motional freedom in hemoglobin than in myoglobin. Finally, PAC quadrupolar asymmetry parameter values show that the electron distribution about the central metal atom is axially symmetric in reconstituted In–Mb, but not in reconstituted In–Hb.
Third-order susceptibility determination by third harmonic generation. II
Authors: Meredith G. R. , Buchalter B. , Hanzlik C.
Published: February 2003

A simple method for determining the third-order nonlinear optical susceptibility of solutions by optical third harmonic generation (THG) is presented. The method utilizes the weak absorption of light by most liquids at the 1.91 μm wavelength of the fundamental employed in this work. This property simplifies the complex interferences between THG arising in all materials (e.g., the cell windows and the solution) in the focal region. χ(3)1111 (−3ω,ω,ω,ω) values of several neat organic liquids are reported. The results are discussed in relation to bond and group additivity in the orientationally averaged second hyperpolarizability.
Variational bounds for polymer transport coefficients
Authors: Fixman Marshall
Published: February 2003

Upper and lower variational bounds are derived for certain polymer transport coefficients, such as the sedimentation constant and intrinsic viscosity. These bounds require the equilibrium averages of complicated functions of configuration, and are generally calculable only from equilibrium computer simulations. The upper bounds contain the steady state bead velocities as trial parameters. When these velocities are taken to arise from rigid body motion, Zimm’s algorithms [Macromolecules 13, 592 (1980)] for the sedimentation coefficient and intrinsic viscosity [η] are recovered. Zimm’s formula for [η] has previously been shown to be an upper bound by Wilemski and Tanaka [Macromolecules (in press, 1981)]. The lower bounds are of two forms. The first is obtained from perturbation theory, and contains any positive-definite and symmetric bead diffusion matrix, e.g., a preaveraged diffusion matrix, as the variational parameters. The second form is derived similarly to the lower bound on the sedimentation constant obtained by Rotne and Prager [J. Chem. Phys. 50, 4831 (1969)], for which the variational parameters specify the perturbed distribution function. Their approach is generalized to include the intrinsic viscosity. Numerical illustrations for Gaussian chains with fluctuating hydrodynamic interaction are reported in the following paper.
Disproof of extreme enhancement of electronic third order hyperpolarizability in TCNQ
Authors: Meredith G. R. , Buchalter B.
Published: February 2003

The orientational average of electronic third-order hyperpolarizability in 7,7,8,8-tetracyanoquinodimethane (TCNQ), γ̃TCNQ, was investigated by optical third harmonic generation. Characterization of solutions containing TCNQ established limits on γ̃TCNQ which, when compared to nonlinear polarizability of other compounds, are much smaller than recent calculations [E. F. McIntyre and H. F. Hameka, J. Chem. Phys. 70, 2215 (1979)] suggest.
Legendre transforms and constrained search constructions of density functionals
Authors: Nalewajski Roman F. , Carlton Terry S.
Published: February 2003

The formal construction of functionals defined within density functional theory is discussed. Two different methods are compared, namely the legendre transforms 9,10 and density-onstrained Search 1 method of Hohenberg-Kohn2.(AIP)
A second generalized equipartition theorem
Authors: Phillies George D. J.
Published: February 2003

An extension of Tolman’s generalized equipartition theorem, allowing the calculation of the mean-square energy and its fluctuations, is demonstrated. Several examples, not all in canonically conjugate coordinate systems, are presented.
Two-component bimolecular systems cannot have limit cycles: A complete proof
Authors: Póta Gy.
Published: February 2003

By applying Dulac’s criterion a proof is presented for the statement that in the case of two-component bimolecular reaction systems, the phase plane cannot contain limit cycle.
Electron diffraction studies of supersonic jets. IV. Conformational cooling of n-butane
Authors: Heenan Richard K. , Bartell Lawrence S.
Published: February 2003

Expansions through small tapered nozzles (∼10−2 cm inlet diameter) have produced conformational cooling of gas phase n-butane to estimated conformational temperatures as low as 180 K. Relaxation into the lower energy trans form was seen with neat butane and with addition of up to ∼30% helium or neon. Thin plate nozzles of comparable diameter do not seem to produce the same effects, presumably because the more rapid cooling they bring about is accompanied by many fewer collisions. Conformational analyses carefully checked for and took into account butane cluster scattering, which if present and ignored, artificially increases the apparent trans mole fraction. At higher concentrations of monatomic carrier gas the cluster scattering becomes strong enough to interfere seriously with the determination of conformational composition. Analysis of the present data and a reanalysis of earlier, conventional, gas electron diffraction data both gave the room temperature trans mole fraction as 64% (3σ=9%) in agreement with a recent spectroscopic inference of 68%.
Periodic precipitation and coarsening waves: Applications of the competitive particle growth modela)
Authors: Feeney R. , Schmidt S. L. , Strickholm P. , Chadam J. , Ortoleva P.
Published: February 2003

It has been shown earlier that the competitive growth dynamics of particles in a sol can account for spontaneous precipitation patterns that arise as a uniform sol ages. Here it is found that this dynamics can, unlike the classic Ostwald–Prager theory, account for a complete range of precipitation pattern types including Runge–Liesegang bands, invert bands, secondary banding, spontaneous pattern formation from a uniform sol and propagation, and destabilization of fronts of coarsening. Effects of electrical fields on banding are also investigated. A characteristic length is obtained and is found to be a strictly nonlinear effect.
Theoretical study of AlH+: Spin splitting, core polarization, and interstellar chemistry
Authors: Cooper David L. , Black John H. , Everard Marcus A. L. , Richards W. Graham
Published: February 2003

The spin splitting constant for the X 2Σ+ state of AlH+ is calculated to be γ0=0.058 cm−1. The favorable comparison of this result with experiment indicates that the uncertainty in the previously calculated spin splitting in MgH is likely to be of the order of a few percent. Calculations are presented of the so-called core polarization contribution to the spin-orbit coupling constant in the A 2Πr state of AlH+. Results are also given for MgH and SiH. Astronomical applications of such calculations are discussed and the abundances of aluminum-bearing molecules in interstellar clouds are estimated.
Dipole interaction of an unequally spaced multilevel atom with a monochromatic electromagnetic field
Authors: Levine A. M. , Schreiber W. M. , Weiszmann A. N.
Published: February 2003

The solution is obtained for the fully quantized dipole interaction between monochromatic photons in the number representation and a multilevel atomic system with unequal energy level spacing. An operator form of the rotating wave model is used. Specific results for three-level and four-level systems are presented.
Atomic kinetic energy functional in density functional theory
Authors: Ohwada Ken
Published: February 2003

With the purpose of finding a better kinetic energy functional in density functional theory, the first-order reduced density matrix for atoms is considered and its approximate form which is composed of the exponentially decreasing functions is proposed as follows: ρ(r‖r′=Σnρn(r‖r′), (A) where n is the principal quantum number ρn′s are the first-order reduced density matrices and assumed as ρn(r‖r′)=An exp [−(Bn+iCnfn)r −(Bn−iCnfn)r′], (B) An, Bn, and Cn being the slowly varying functions of r and r′, and fn the function depending on the principal quantum number. From Eqs. (A) and (B), a reasonable kinetic energy functional is derived as T[ρ]=Σn1/8ℱ∇ρn∇ρn/ρndr +Σn3(3π2)2/3/10 f2nℱρn5/3 dr. (C) It is shown that the functional is adequate for describing the long-range behavior as well as the nuclear-cusp behavior of ρ(r), and also for the prediction of the electronic kinetic energies for atoms.
Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. I. Second-order perturbation treatment for He, Be, H2, and LiH
Authors: Szalewicz Krzysztof , Jeziorski Bogumil , Monkhorst Hendrik J. , Zabolitzky John G.
Published: February 2003

Second-order correlation energies for He, Be, H2 and LiH were calculated variationally using a novel functional and a basis set of explicitly correlated Gaussian geminals. Each geminal was a product of two spherical Gaussian orbitals and a correlation factor of the form exp(−γr212). Since the time-consuming terms resulting from the strong orthogonality do not appear in our functional, basis sets much larger than previous ones could be handled. The second-order energies obtained after carefully optimizing all nonlinear parameters are better than the best values published hitherto in the literature, although the improvement is marginal for He and Be. This shows that the present approach is able to match the ‘‘basis set independent’’ results available for atoms, providing at the same time a similar accuracy for small molecules. The proposed approach offers a sensible alternative to the virtual orbital expansion method customarily used in MBPT calculations, since, for obtaining a comparable accuracy, orbitals much higher than f would have to be used in expanding the pair functions.
Nonlinear noise analysis in nuclear magnetic resonance spectroscopy. 1D, 2D, and 3D spectra
Authors: Blümich B. , Ziessow D.
Published: February 2003

The nuclear spins of a sample in a magnetic field are treated as the contents of a black box which upon rf excitation delivers transverse magnetization in a nonlinear fashion. The system response is expanded into an integral series. The Fourier transforms of the kernels of the integrals define multidimensional spectra which describe the nonlinear properties of the system. An expansion of the time dependent density matrix reveals that connections between three transitions via common energy levels give rise to peaks in the three-dimensional third order spectrum. Connections between two different transitions produce cross peaks on subdiagonal planes of the 3D spectrum. For some simple spin systems such 2D spectra have been computed from the measured response to binary noise excitation. They exhibit cross peaks for lines connected by chemical exchange or indirect coupling. It is shown that the noise experiment is advantageous in as much as efforts in measuring (magnet time) are shifted to computing (processor time). Only a few parameters need to be specified for the experiment, whereas there are various options for the numerical evaluation of the acquired data.
Cooperative two-photon absorption
Authors: Andrews David L. , Harlow M. J.
Published: February 2003

It is well known that irradiation with intense laser light can lead to nonlinear absorption processes by individual molecules. However, the mutual interaction between two molecules can lead to cooperative nonlinear processes which result in entirely new features in the absorption spectrum. In this paper, the theory of cooperative two-photon absorption is developed using the principles of quantum electrodynamics, and expressions are derived for the rate of cooperative absorption for transitions which are forbidden in the absence of any such interaction. Several different cases are examined in detail, including crystalline or matrix-isolated species, gaseous and liquid mixtures, and van der Waals molecules. It is shown that the cooperative absorption rate can be substantially increased by choosing materials with suitable energy levels where one of several resonance enhancement mechanisms can be exploited. Finally, methods of observation are discussed, and a specific photochemical example is given for the case of a mixture of formaldehyde and deuterioformaldehyde.
NMR study of molecular motions in perisubstituted naphthalenes
Authors: Imashiro Fumio , Takegoshi Kiyonori , Okazawa Sachiko , Furukawa Jun , Terao Takehiko , Saika A. , Kawamori Asako
Published: February 2003

Molecular motions in solid 8-substituted 1-methylnaphthalenes with the substituents H, CH3, Cl, and Br have been investigated by the temperature dependence of the 1H spin-lattice relaxation times and of the 1H second moments and high-resolution solid-state 13C NMR spectra with or without magic-angle sample spinning. The observed barriers to rotation of the perimethyl groups increase in the order of H (2.30 kcal/mol)≪CH3 (3.22)<Cl (3.61)<Br (4.37), which is in line with the sequence of the van der Waals radii. The halogenated methylnaphthalenes are found to undergo in-plane molecular rotation with relatively low activation energies (4.5–4.7 kcal/mol). Molecular motions in 1,4,5,8-tetramethylnaphthalene are also discussed.
Laser induced fluorescence spectra of the a 3Πu–X 1Σ+g band of Na2 by molecular beam
Authors: Shimizu Kazuko , Shimizu Fujio
Published: February 2003

Laser induced fluorescence spectra of the a 3Πu–X 1Σ+g band of Na2 are studied using the crossed molecular beam and laser technique in the wavelength region 14 700–16 000 cm−1. All band origins of a 3Πu0–X 1Σ+g, v″=0 transitions in this wavelength region are observed. Their wavelengths are tabulated and analyzed.
Microwave, infrared, and Raman spectra, structure, and normal coordinate analysis of ethylstannane-d and ethylstannane-d3
Authors: Durig J. R. , Li Y. S. , Sullivan J. F. , Church J. S. , Bradley C. B.
Published: February 2003

The microwave spectra of CH3CH2SnH3 and CH3CH2SnD3 for the five most abundant isotopes of naturally occurring tin, 116Sn, 117Sn, 118Sn, 119Sn, and 120Sn, have been recorded in the range 18.0–40.0 GHz. Only a-type transitions were identified and R-branch assignments have been made for the ground vibrational state. The components of the dipole moment were determined from the Stark effect to be ‖μa‖=0.86±0.01 D, ‖μb‖=0.48±0.04 D, and ‖μt‖=0.99±0.02 D. No splittings in the ground state were observed due to the internal rotation of either the SnH3 or CH3 tops. Based on this observation, lower limits to the barriers to internal rotation of 1.12 and 2.12 kcal/mol are estimated for the SnH3 and CH3 tops, respectively. The following five structural parameters were determined from a least-squares fit of the 20 rotational constants (B and C only): r(Sn–C)=2.143±0.003 Å; r(C–C) =1.552±0.025 Å; ∢HSnC=109.5±0.1°; ∢HCH=107.5±3.9°; ∢SnCC=112.6±0.9°. The Raman spectra (3200–10 cm−1) were obtained for all three phases and infrared spectra (3200–80 cm−1) were obtained for the gas and solid. An assignment is proposed based on band contours, depolarization values, isotopic shifts, and group frequencies for all the normal modes except the two internal torsions; however, the methyl torsion in CH3CH2SnD3 has been tentatively assigned to a band observed at 242 cm−1 in the infrared spectrum of the solid. A normal coordinate calculation was carried out by utilizing a modified valence force field with 30 internal coordinates and 21 force constants. The observed frequencies are fit to better than 1%. The observed splitting of the normal modes in the spectra of the solids along with the number of observed lattice modes is consistent with two molecules per primitive cell. The results are compared to corresponding quantities in some similar molecules.
Competition between isomerization and fragmentation of gaseous ions. II. Nitromethane and methylnitrite ions
Authors: Gilman Jerome P. , Hsieh Tacheng , Meisels G. G.
Published: February 2003

Major fragmentation pathways of the nitromethane and methylnitrite ions have been examined. Ionization and fragmentation onsets for these processes have been determined and breakdown graphs have been constructed for both compounds using a threshold photoelectron–photoion coincident (TPEPICO) mass spectrometer. At onset, fragmentation of the nitromethane ion to NO+ is preceded by isomerization to the energetically favored methylnitrite ion; the barrier to isomerization is 0.64 eV. Symmetry considerations indicate that the nitromethane ion in its 2A2 (π) state correlates with the 2A″(π) state of the methylnitrite ion through which dissociation to the NO+ fragment occurs.
Reply to the ‘‘Comment on few-atom 3He–4He mixed molecules’’
Authors: Nakaichi-Maeda S. , Lim T. K. , Akaishi Y. , Tanaka H.
Published: February 2003

The binding energy of 3He(4He)2 is recalculated with more correct ℏ2/M values. The Smith-Thakkar, HFDHE2, and mDD-2 potentials ensure its binding, while the Beck, Lennard-Jones, and ESMMSV potentials do not.
Measurement and calculation of rotational relaxation rate constants in the ground and excited vibrational states of HCOOH
Authors: Minowa Tatsuya , Matsuo Yukari , Kuze Hiroaki , Shimizu Tadao
Published: February 2003

The transverse relaxation rate constants of the rotational transitions of HCOOH, 101←000, 202←101, 211←110, 312←313, 413←414, and 514←515 in the ground state and 101←000 in the ν9 vibrationally excited state are measured by a microwave coherent transient spectrometer. Highly sensitive detections of weak transitions are achieved by new methods of stabilizing the center frequency of modulated microwave and of removing the background noise. No remarkable difference between the rate constants of the ground and excited vibrational states is found. The collisional relaxation among considerably dense energy levels are theoretically investigated on the basis of the impact theory, where only the dipole–dipole interaction is considered. Contributions from a large number of rotational levels are taken into calculations of the cross sections. A good agreement between the experimental and the theoretical results is obtained.
Conductance correlation analysis of kinetics of nickel lactate complex formation
Authors: Ohbayashi Kohji , Minoda Masaharu , Murakami Kiyofumi , Yasunaga Tatsuya
Published: February 2003

Conductance correlation analysis is applied to nickel lactate complex formation. The correlation function of the potential fluctuations are observed as the function of the concentration. The relaxation times observed agree well with those obtained by the pressure jump method. The concentration dependence of the amplitudes of the correlation functions is consistent with theory.
EUV studies of N2 and O2 produced by low energy electron impact
Authors: Morgan H. D. , Mentall J. E.
Published: February 2003

The emission spectrum of atomic nitrogen (NI), singly ionized atomic nitrogen (NII), atomic oxygen (OI), singly ionized atomic oxygen (OII), and molecular nitrogen (N2) dominates the day airglow and aurora spectrum in the extreme ultraviolet. However, analysis of the excitation of these lines is not possible due to the lack of laboratory or theoretical data for the relevant processes. Absolute emission excitation cross sections resulting from low energy electron impact on N2 and O2 have been measured in the extreme vacuum ultraviolet (500–1200 Å). Electron energies were from 0 to 300 eV. Numerous bands of N2 were found between 800 and 1000 Å. These band systems are of particular interest because their optical oscillator strengths are unusually large and should have large emission cross sections. Excitation functions were measured for the N2 c′ 1Σ+u → X 1Σ+g v′=0−v″=0 band emission, the NII 916 Å multiplet, the OI 879 Å multiplet, and the OII 834 Å multiplet. In addition, cross sections were measured at 200 eV only for several of the band emissions plus the NI 1135 Å, NI 1164 Å, NI 1177 Å, NII 776 Å, NII 1084 Å, OI 1152 Å, OI 1041 Å, OI 1027 Å, OI 999 Å, OI 989 Å, OI 879 Å, OII 834 Å, OII 616 Å, OII 555 Å, OII 539 Å, and OII 718 Å multiplets.