bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic velocities and densities of polycrystalline ice Ih, II, III, V, and VI by Brillouin spectroscopy
Authors: Gagnon R. E. , Kiefte H. , Clouter M. J. , Whalley Edward
Published: July 2002

The longitudinal and transverse speeds of sound of ice Ih, II, III, V, and VI have been measured by Brillouin spectroscopy in the range 0–10 kbar at −35.5 °C. The bulk adiabatic moduli derived from these measurements are 138.9, 98.7, 141.9, and 181.4 kbar for ice II, III, V, and VI, respectively, at pressures of 2.83, 2.76, 4.80, and 7.77 kbar, respectively. The isothermal compressions of the five phases have been measured directly by the contraction of a sample that was confined to a stainless-steel tube.
Rotational energy accommodation and apparent desorption energy of OH formed in the catalytic reaction of NO2 and H2 over Pt(111): Effect of surface oxygen coverage
Authors: Novakoski Leo V. , Hsu David S. Y.
Published: July 2002

Laser induced fluorescence has been used to study the desorption dynamics of OH radicals produced by the reaction of NO2 and H2 on Pt(111), under ultrahigh vacuum conditions. We measure an apparent Arrhenius activation energy for desorption that increases from 25 to 38 kcal/mol as the NO2 to H2 ratio in the dosing mixture decreases from 2 to 0.05. Boltzmann-like rotational energy distributions with relatively high rotational to surface temperature ratios (Tr/Ts =0.69−0.87) are reported for crystal temperatures between 1078 and 1433 K. We have also observed a small but definite dependence of the Tr/Ts ratio on both Ts and the dosing mixture ratio. These results are compared with earlier data from the O2+H2 reaction over Pt(111) and interpreted in terms of O coverage.
A line shape analysis of the effects introduced by motions in the nuclear magnetic resonance spectra of decoupled solids
Authors: Frydman Lucio , Frydman Benjamin
Published: July 2002

An analysis of the effects of a two-site exchange process on the solid-state nuclear magnetic resonance (NMR) spectrum of an S spin coupled to an unlike I spin under rf irradiation is presented. It is shown that the line broadening that under certain conditions is shown by the S resonance can be calculated using a density matrix treatment. Although this approach has been used in order to evaluate the signal that arises from single crystallites, a simplification of the problem was introduced in order to evaluate the signal that arises from a powdered sample. With this approximation it was possible to evaluate the effects of exchange for a broad range of kinetic and decoupling conditions. The calculations were extended to include the effects of the chemical shift anisotropy of the S spins, and simulations obtained in this way agreed well with the experimental spectra of an exchanging solid recorded at different temperatures and decoupling fields. The relation between incoherent and coherent interference with decoupling in solids and in liquids is also briefly discussed.
Collisional quenching of CO+(A 2Π3/2, v′=1) by Ne
Authors: Lemaire Joël , Marx Rose , Parent Denise C. , Chevrier Marc
Published: July 2002

Time resolved laser-induced fluorescence was used to study the quenching of CO+ (A 2Π,v′=1) by Ne. In spite of almost identical collision rates the quenching rate for Ne, kq =(4±1)×10−11 molecule−1 cm3 s−1, is much larger than for He. A tentative interpretation of the large quenching efficiency of Ne is proposed.
A method for the analytic determination of polypeptide structure using solid state nuclear magnetic resonance: The ‘‘metric method’’
Authors: Brenneman M. T. , Cross T. A.
Published: July 2002

A method, the metric method, is presented for determining the structure of polypeptides using solid state nuclear magnetic resonance (NMR) dipolar interactions. In analogy to the method of distance geometry used for protein structure determination from high resolution NMR spectroscopy, which is based on the general relationships that distances between points must satisfy, a method is developed here which makes use of the general relationships that angles between vectors must satisfy. With this method, analytical expressions are derived for the dihedral angles of the peptide backbone, and a way for minimizing the structural ambiguities associated with solid state NMR data is also presented. Calculations on a model polypeptide structure reveal the dipolar interactions of only the NH and NC1 bonds provide insufficient information for uniquely determining dihedral angles, even when constraints arising from long range interactions are employed, but these calculations yield a manageable number of solutions when the CαH interaction is also considered.
On the thermodynamics of dilute dumbbell solutions under shear
Authors: Camacho J. , Jou D.
Published: July 2002

The relation predicted by extended irreversible thermodynamics between the nonequilibrium entropy and the frequency-dependent viscosity is confirmed from kinetic theory for dilute dumbbell solutions under shear. New relations between nonequilibrium entropy and the coefficients of the constitutive equations are discussed.
On the molecular theory of aqueous electrolyte solutions. IV. Effects of solvent polarizability
Authors: Kusalik P. G. , Patey G. N.
Published: July 2002

This paper describes a new level of theory with which to study model electrolyte solutions with a polarizable solvent. The theory considers the average local electric field experienced by a solvent particle as a function of its separation, R, from an ion and is referred to as the R-dependent mean-field (RDMF) approximation. Explicit expressions are derived for model solutions consisting of hard-sphere ions immersed in a hard polarizable dipole tetrahedral-quadrupole solvent. The lateral solvent fields are shown to cancel a large portion of the field generated by the ionic charge. The RDMF gives rise to an effective spherical ion–solvent potential which will affect the low-concentration limiting behavior of certain thermodynamic properties. The reference hypernetted-chain (RHNC) approximation is solved to obtain RDMF/RHNC results at infinite dilution and low concentration for several model aqueous electrolyte solutions. The ion–ion correlations and thermodynamic quantities such as the mean activity coefficient and partial molar volume of the solute are found to be particularly sensitive to the treatment of the solvent polarizability as this level.
The infrared spectrum of trimethylenemethane. Predictions of in-plane vibrational frequencies from correlated wave functions
Authors: Blahous Charles P. , Xie Yaoming , Schaefer Henry F.
Published: July 2002

The infrared vibrational spectrum of trimethylenemethane (TMM) is predicted with self-consistent field and configuration interaction methods. The 3A′2 electronic ground state of TMM is described in terms of restricted Hartree–Fock theory and in light of experimental evidence. Analytic gradient methods are employed to optimize theoretical geometries for 3A2 TMM; vibrational frequencies are evaluated via analytic second-derivative techniques (self-consistent-field) and finite differences of analytic gradients (configuration interaction). The resulting IR-spectral predictions are modified to reflect average errors statistically associated with the two theoretical methods.
Rydberg–Klein–Rees potential curves: Error analysis and a correction scheme
Authors: Pajunen Petri
Published: July 2002

The fundamental source of error in the Rydberg–Klein–Rees inversion procedure of diatomic spectroscopy is the first-order phase integral or WKB approximation on which it is based. In this article, errors due to this approximation are analyzed and a simple correction scheme is proposed. The method computes correction functions to account for the differences between the first-order and exact energies and rotational constants which are used for the input of the RKR equations corresponding to first-order values in terms of the exact experimental values and the correction function above.
Inhomogeneous perturbations and phase resetting in an oscillatory reaction–diffusion system
Authors: Chee Merk-Na , Kapral Raymond , Whittington Stuart G.
Published: July 2002

The response of the Brusselator reaction–diffusion system to inhomogeneous perturbations is studied. The main focus of this work is on a spatial generalization of the phase resetting problem. A randomly chosen fraction p of an initially homogeneous oscillatory system is locally perturbed and driven off the limit cycle. The asymptotic local phase is monitored and averaged over local regions and realizations of the perturbation process. From this information a phase response curve can be constructed which depends both on the local stimulus amplitude and on p. The system exhibits two qualitatively different kinds of response depending on the stimulus amplitude and the phase at which the perturbation is applied. It either relaxes to a spatially homogeneous oscillatory state or develops persistent spatial patterns. The origin of this behavior is discussed.
Photodissociation spectroscopy of the [OCS⋅C2H2]+ cluster ion
Authors: Orlando Thomas M. , Friedmann Adrian , Maier John P.
Published: July 2002

The potential-energy surface features involved in the [OCS+C2H2]+ reaction system allow a metastable enroute to reaction to be trapped. The absolute photodissociation spectrum of this trapped metastable [OCS⋅C2H2]+ cluster ion has been measured in the wavelength region between 375 and 735 nm using a coaxial-laser–triple-quadrupole ion-beam apparatus. The photodissociation spectrum consists of at least three broad overlapping profiles, and OCS+, C2H+2, and C2H2S+ are the observed ionic photoproducts. The spectrum is interpreted in terms of transitions to excited charge-transfer states which are repulsive and to a dissociative transition which is localized on the perturbed OCS+ moiety. The C2H+2 fragment becomes detectable within sensitivity limits at 1.69 eV, yielding an upper limit estimate of 1.46 eV (+0.15/−0.23 eV) for the cluster bond dissociation energy. The C2H2S+ product is only observable at photon energies greater than 2.74 eV and is considered to be the product of a photoinitiated intracluster ion–molecule reaction.
Orientational ordering of free chains in a dense polymer network
Authors: Edwards S. F. , McLeish T. C. B.
Published: July 2002

The statistics of a polymer solvent in a network are investigated. We find that, without any explicit nematic interaction, the free chains are coupled to the orientation of the network via the excluded volume interaction. Because their conformations are dominated by screening, the minimum in the free energy of the solvent chains is found by following the network. This first paper considers a rigid network frozen from an earlier equilibrium configuration. In the limiting case of the melt the change in the scattering function is ΔS(k)=12VcscN(cS+cN)−1 l−2[(E⋅k)−2−k−2], where cS and cN are the concentrations of solvent and network, l is the Kuhn length, and E is the strain tensor. In the case of a swollen network, the full scattering pattern may assume the ‘‘lozenge’’ appearance noticed by several workers.
Transformation of benzene to a polymer after static pressurization to 30 GPa
Authors: Pruzan Ph. , Chervin J. C. , Thiéry M. M. , Itié J. P. , Besson J. M. , Forgerit J. P. , Revault M.
Published: July 2002

After pressurization to 30 GPA, in a diamond anvil cell, benzene transforms, at room temperature, to a white solid which is stable at ambient pressure. We report here the infrared spectroscopy analysis performed under pressure and at ambient conditions. These preliminary results show that the transformation involves an opening of the benzene rings leading to a highly cross-linked polymer.
Monte Carlo test of electrostatic persistence length for short polymers
Authors: Reed Christopher , Reed Wayne
Published: July 2002

A Metropolis Monte Carlo program with reptation is used to generate sample configurations of short electrically charged polymers with thermally distributed Debye–Hückel electrostatic energies. The polymer is a three fold rotational isomeric state model with bond angle θ between 5° and 90° and number of units N between 10 and 225. To compare the resulting root-mean-square (rms) values for radius of gyration S, and end-to-end length R, to theory, we use a wormlike chain with contour length L equal to the stretched out length of the polymer, the same total charge, and an intrinsic persistence length set so that, for large N, for specified θ and L, S agrees with the rotational isomeric state model. The results are compared with the predictions for S, with correction for finite L, of Odijk [J. Polymer Sci., Polymer Phys. Ed. 15, 477 (1977)]. They are then compared with three attempted corrections for excluded volume: (1) Odijk and Houwaart [J. Polymer Sci., Polymer Phys. Ed. 16, 627 (1978)]; (2) correction (1) modified by using the electrostatic excluded volume of Fixman and Skolnick [Macromolecules 11, 863 (1978)]; (3) correction (2) modified by replacing the Yamakawa–Tanaka formula by an approximation due to Gupta and Forsman [Macromolecules 5, 779 (1972)]. Odijk’s prediction with correction for finite length works fairly well under conditions of small excluded volume. The excluded volume corrections are often but not always of about the right size; the latter two work better.
Equilibrium dimensions of polymers in quenched disorder
Authors: Cherayil Binny J.
Published: July 2002

The mean square end-to-end distance 〈R2〉Q of a good solvent solution of a single polymer in the presence of a quenched distribution of point scatterers is calculated to first order in ε=4−d by renormalization group methods. As the volume of the system becomes infinite, the quenched and annealed averages of the chain dimensions are shown to coincide, and the effect of disorder is seen essentially to generate a renormalized excluded volume interaction that, depending on its strength, leads to chain statistics characteristic of good, theta or marginal solvent conditions. At intermediate values of the volume, the chain is effectively collapsed, but there is no universal asymptotic scaling law that this behavior corresponds to. The size of the chain in this regime is predicted to vary with the square root of the volume, in contrast to the logarithmic variation predicted by Cates and Ball on the basis of mean field arguments.
Molecular arrangements and conformations of the alkyl chains in spherical micelles and droplets
Authors: Vacatello Michele , Yoon Do Y.
Published: July 2002

We have modeled two systems of spherical micelles and of n-alkane droplets, each consisting of 52 molecules comprised by 13 units each in a spherical region of approximately 1.6 nm radius, by the Monte Carlo simulation method. The simulated model micelle exhibits the distribution of chain segments in good agreement with the results of neutron scattering and NMR experiments on micelles having similar compositions. Both the micelle and the droplet models show that the segments in the interior of the chains tend to stay away from the interfaces, resulting in enhanced chain-end densities at the surface region. Moreover, chain segments in contact with the interface tend to orient along the interface,thus exhibiting negative order parameters with respect to the radius vector. Despite this local anisotropic orientation, however, the average conformation of the alkyl groups is only slightly different from that of the unperturbed random-coil model.
Electron beam initiated discharges in HN3 gas mixtures
Authors: Schlie L. A. , Wright M. W.
Published: July 2002

The behavior of electron beam initiated discharges in HN3 and inert gas mixtures for different E/N values are presented. These results are the first reported investigations of this highly energetic azide gas under plasma conditions. Using a 3 ns, 600 KeV ionizing electron beam, the temporal decay of the discharge current shows HN3 is electronegative. HN3 attachment rate constants in Ar are 5.0–10.0×10−11 cm3 s−1 for E/N values in the range 1–4 Td (10−17 V cm2). With the other inert gases (He, Ne, Kr, and Xe), HN3 attachment rate constants are 0.5–4.5×10−10 cm3 s−1 for the E/N range of 0.5–7.0 Td. Plasma excitation of Ar and HN3 gas mixtures produce intense N2(C→B, v′=0→v″=0) electronic transition radiation at 3371 Å.
Substituent effects on the electronic spectroscopy of tryptophan derivatives in jet expansions
Authors: Tubergen Michael J. , Cable J. R. , Levy Donald H.
Published: July 2002

Electronic excitation spectra of seven tryptophan derivatives entrained in a supersonic expansion have been recorded using both resonantly enhanced two-photon ionization and laser induced fluorescence. Two derivatives, tryptophan amide and tryptophan methyl amide, were found to have substantial low frequency vibrational progressions in their excitation spectra, yet in both compounds this behavior was apparent in only one conformer. Other derivatives did not display as much vibronic activity. Conformers which had vibrational progressions were found to emit in a broad band far to the red of excitation. All other conformers were found to fluoresce most strongly in resonance with excitation. The presence of low frequency vibrational activity and red shifted fluorescence correlates well with the ability of the derivative to form an intramolecular hydrogen bond between the amine and the carboxylic acid. Backbone conformers that contain an intramolecular hydrogen bond are expected to have large dipole moments, which may strongly perturb the electronic structure of the indole chromophore.
Mössbauer and electron paramagnetic resonance study of the double-exchange and Heisenberg-exchange interactions in a novel binuclear Fe(II/III) delocalized-valence compound
Authors: Ding Xiao-Qi , Bominaar Emile L. , Bill Eckhard , Winkler Heiner , Trautwein Alfred X. , Drüeke Stefan , Chaudhuri Phalguni , Wieghardt Karl
Published: July 2002

In this paper we present the characterization by UV-VIS, Mössbauer, and EPR spectroscopy of [L2Fe2(μ-OH)3](ClO4)2⋅2CH3OH⋅2H2O, with L=N,N′,N″-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which is shown to possess a central exchange-coupled delocalized-valence Fe(II/III) pair. Complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. Mössbauer, EPR, and magnetic susceptibility data imply a system spin St =9/2 for the ground state. This finding is explained as being a consequence of the double-exchange interaction which is generated by the delocalized electron. Experimental values obtained from UV-VIS, Mössbauer, and EPR spectroscopy are for the double-exchange parameter B=1300 cm−1, the g factors gx,y =2.04 and gz =2.3, the parameters for zero-field splitting D=4 cm−1 and E≊0 cm−1, and for the hyperfine parameters ΔEQ =−2.14 mm s−1, Ax,y =−21.2 T, Az =−27 T, and δ=0.74 mm s−1. From our temperature-dependent studies we assign to the first excited state a spin-octet with an excitation energy Δ>175 cm−1. From this value a lower bound of −235 cm−1 has been deduced for the exchange-coupling constant J. In the framework of a simplified description of the iron atoms by unperturbed 3d orbitals, the values of the A tensor components as well as the quadrupole splitting ΔEQ can be interpreted in a consistent manner by assuming the excess electron being delocalized over two dσ orbitals centered at the two iron sites of the dimer and directed along the iron–iron axis as the z direction.
Coadsorbate effects in surface photochemistry: NO and O2 on Pt(111)
Authors: Mieher W. D. , Ho W.
Published: July 2002

Photon-induced desorption (PID) and electron energy loss spectroscopy (EELS) applied to the system NO/O2/Pt(111) yield information on coadsorbate effects in surface photochemistry. A new NO species (denoted γNO) is observed in EELS [νγN−O=236 meV, ν(Pt−γNO)=49 meV], and is found to have a highly enhanced PID cross section compared to that of NO in the top sites of the clean surface [σγNO(O2)(333 nm)=(1.1±0.1)×10−18 cm2]. Photodesorption of O2 is enhanced and photodissociation of O2 is inhibited in the presence of NO resulting in the suppression of NO2 production upon irradiation of NO/O2/Pt(111), in contrast to the photoinduced formation of CO2 from CO/O2/Pt(111). The wavelength dependences of NO and O2 PID cross sections demonstrate that they are independent processes. The final product states created in photoinduced processes with O2 are strongly influenced by coadsorbates.
Elastic property of the lamellar structure in block copolymer melt added selective homopolymer chains
Authors: Ohta Takao
Published: July 2002

Statistical property of the microphase separated phase in copolymer-homopolymer mixtures is investigated in the strong segregation limit. The elastic constant of the lamellar structure influenced by the selective homopolymer chains is calculated for the block ratio f=1/2 of the block copolymer. The concentration profile of the added homopolymer chains is also obtained. The approximation used is the volume fraction expansion of the homopolymer and the weak interaction between the copolymer and the homopolymer is assumed.
Theoretical dipole moment functions involving the a 3Π and a′ 3Σ+ states of carbon monoxide
Authors: Peterson Kirk A. , Woods R. Claude
Published: July 2002

Potential energy and dipole moment functions have been calculated for the first two excited electronic states of CO by several ab initio methods using large Gaussian basis sets. Similar calculations on the ground state have also been performed to provide a basis for comparison. The types of calculations on the a 3Π state included complete active space self-consistent field (CASSCF), single reference single and doubles configuration interaction (CI-SD) including a size consistency correction [CI-SD(s)], quadratic CI-SD (QCI-SD), and quadratic CI-SD including the effects of triple excitations [QCI-SD(T)], and version 1 of the coupled electron pair approximation (CEPA-1).The best calculated dipole moment functions for the a 3Π state have been found to be consistent with earlier theoretical results with respect to shape (slope, μ′e), and also more accurate in predicting the equilibrium value μe. Theoretical dipole moment functions for the a′ 3Σ+state are presented for the first time, at the CI-SD, CI-SD(s), and CASSCF levels of approximation. The first two of these yield estimates of μe that are in very good agreement with that derived from the analysis of perturbations in the molecular beam electric resonance (MBER) Stark effect of the a 3Π state. The (a–a′) electronic transition moment has also been calculated at the CASSCF and CI-SD levels. Our CASSCF value of 0.23 D (v″=4, v′=0) compares well with values derived from the MBER Stark effect.
Theoretical study of the free energy curve as a function of reaction coordinate of electron transfer by the cumulant expansion method
Authors: Yoshimori Akira , Kakitani Toshiaki
Published: July 2002

We investigate the free energy curve as a function of the reaction coordinate of the electron transfer by the cumulant expansion method. The deviation from the linear response which gives rise to a harmonic form of the free energy curve is expressed in terms of the cumulants. The validity condition of the linear response is investigated using the l-particle correlation length λl. It is a central result that the linear response applies only when the conditions λ2 ≫ λl(l ≥ 3) and λ2≫a hold, where a is the sum of solute and solvent radii.
Experimental determination of thermal and nonthermal mechanisms for laser desorption from thin metal films
Authors: Li Yunzhi , McIver Robert T. , Hemminger John C.
Published: July 2002

The mechanism of laser desorption of peptides as negative ions from Au thin films with 193, 248 and 351 nm laser radiation has been studied. Variation of the threshold laser power density with metal film thickness is used to distinguish between thermal and nonthermal mechanisms. The influence of laser wavelength on the desorption of peptides with different optical absorption spectra has been studied. Thermal desorption is observed when 351 nm laser radiation is utilized. However, both 248 and 193 nm radiation result in nonthermal desorption processes. At 248 nm, the threshold power density is observed to be independent of the optical absorption of the peptide adsorbate, supporting suggestions that a mechanism involving excitation of hot electrons in the metal is important.
Effect of solvent polarity on a rotational isomerization mechanism of rhodamine-B in normal alcohols
Authors: Chang Tzyh-Lee , Borst Walter L.
Published: July 2002

Experiments were performed to investigate the effects of solvent polarity and solvent viscosity on the nonradiative rates of rhodamine-B in a series of normal alcohols. The fluorescence quantum yields and lifetimes for rhodamine-B in these solvents were measured and used to calculate the nonradiative rates. From a modified kinetic model, the nonradiative rate can be deduced to be the conversion rate for crossing over a potential barrier from an excited planar state to an excited twisted state. Both solvent viscosity and solvent polarity can play key roles in this mechanism because the former may hinder the rotational motion and the latter may change the barrier height. Our results show that the variation in the nonradiative rates is due to solvent polarity changes rather than to solvent viscosity changes. The effect of solvent viscosity on the excited-state lifetimes of rhodamine-B in a series of methanol–poly(ethylene oxide) mixed solvents was also investigated. Our results indicate that the measured lifetimes are essentially independent of solvent viscosities, which in turn indicates that solvent viscosities have no significant effect on the nonradiative rates.
A beam scattering study of the dynamics of CH+4(CH4,CH3)CH+5 reaction in the eV collision energy range: Three competing mechanisms of CH+5 formation
Authors: Herman Zdenek , Henchman Michael , Friedrich Bretislav
Published: July 2002

A crossed-beam study of the reaction CH+4(CH4,CH3)CH+5 was carried out in the collision energy range 0.6–2.3 eV. Three distinct patterns were observed, which may be interpreted in terms of three competing mechanisms for CH+5 formation: proton stripping, H-atom pickup, and intermediate complex decomposition. The existence of a C2H+8 intermediate, stable towards dissociation, is suggested by the results. The relative weights of the three mechanisms were estimated as a function of collision energy.
Determination of hyperfine interactions from the magnetic field dependence of nuclear modulation frequencies: An electron spin echo envelope modulation study of protons in γ-irrradiated potassium dihydrogen arsenate
Authors: Gerfen Gary J. , Singel David J.
Published: July 2002

A study is presented of the field dependence of proton ESEEM (electron spin echo envelope modulation) of the AsO4−4 center in γ-irradiated single crystals of KDA (potassium dihydrogen arsenate). Modulation patterns and corresponding spectra were registered over the range of external field strengths spanned by the nominally allowed EPR transitions (∼3.5 kG) with the field orientation selected along the crystallographic c axis. By tracking the external field dependence of the ESEEM frequencies of the protons attached and hydrogen-bonded to the AsO4−4 center, the absolute value of both the secular and nonsecular portions of their hyperfine interactions, as well as the sign of the secular component, are determined. The results are compared with those obtained by ENDOR (electron-nuclear double resonance) spectroscopy. The implications of this work for the determination of the magnitudes and signs of the elements, principal values, and direction cosines of the principal axes of hyperfine interaction matrices in orientationally disordered solids are discussed in detail. The large hyperfine coupling to the 75As nucleus has important ramifications upon the ESEEM spectroscopy and its analysis. In general, such couplings increase the breadth of the EPR spectrum and thereby facilitate the survey of ESEEM field dependences; they can also seriously complicate the analysis of the ESEEM results by precipitating significant deviations between the magnitude of the expectation value of the electron spin angular momentum and its nominal value, MS: ESEEM frequency expressions in which these two quantities are implicitly equated are not generally applicable. This issue is commented on in detail. Expressions are derived and discussed that elucidate the effect of a large hyperfine coupling on the magnitude of the expectation value of the electron spin, its deviations from MS, and the consequent shifts in ESEEM frequencies. Experimental situations in which these deviations and shifts are negligible are delineated. These effects are illustrated with the results of our 1H ESEEM study of the AsO4−4 center in KDA.
Detection of parity-forbidden excited states by preresonance Raman excitation: Diphenyldecapentaene
Authors: Sztainbuch Isaac W. , Leroi George E.
Published: July 2002

The presence of dipole-forbidden (‘‘hidden’’) excited electronic states in centrosymmetric chromophores can in principle be inferred from preresonance Raman excitation profiles (REPs). As the excitation radiation is tuned through the appropriate energy range, vibronic coupling between the state of interest and nearby ‘‘allowed’’ electronic states will produce interference effects in the ground state scattering intensity. We have used the Kramers–Heisenberg dispersion relation to establish a one-to-one correspondence between the vibrational modes of the 2 1Ag excited state and the interference features in the experimental preresonance REP of all-trans diphenyldecapentaene (DPDP). The parameters utilized to predict the REP of DPDP were obtained without adjustment from absorption and fluorescence excitation spectra. The satisfactory representation and interpretation of the structure in the experimental spectrum establishes preresonance Raman excitation as a viable technique for characterizing such hidden states in non-fluorescing molecules.
Projected unrestricted Mo/ller–Plesset second-order energies and gradients
Authors: Handy Nicholas C. , Su Ming-Der , Coffin Jamie , Amos Roger D.
Published: July 2002

The removal of spin contamination from unrestricted Hartree–Fock Mo/ller–Plesset calculations is now recognized to be important. Here the Handy–Knowles formulation, previously presented, is studied. An evaluation of the energy and the energy gradient, for the removal of one- and two-spin contaminants, is described. The cost of the algorithm for the gradient is proportional to n2v3, where n and v are the number of occupied and virtual orbitals, respectively. Applications of this algorithm are presented for CN, Li3, and the abstraction of H from CH4.
Classical path approximation for one-electron Green’s function in a magnetic field and the density functional model
Authors: Li Shiwei , Percus J. K.
Published: July 2002

This paper is an extension of our previous work on density functional models of electrons in magnetic fields. A full ‘‘classical path’’ (CP) one-body Green’s function is used in the calculation of the kinetic functional and the one particle density. This treatment leads to a more precise expression of the density functional theory in the strong B case, in which magnetic fields are much stronger than the external scalar potential. In the semiclassical limit t→0, the CP Green’s function is checked by an exact solvable system, interactionless electrons in a central harmonic potential and a constant magnetic field. It turns out that the Green’s function is correct through the order O(t2). Furthermore, in the high B limit (but still t→0), the leading terms in B of the CP Green’s function are the same as those of the exact Green’s function in the entire t-expansion series.
HF–HF differential scattering cross sections
Authors: Vohralik Peter F. , Watts R. O. , Alexander Millard H.
Published: July 2002

Close-coupled scattering calculations have been carried out for collisions between HF molecules in their ground vibrational state at a total energy of 1480 cm−1. State-to-state integral and differential cross sections were determined for transitions j1j2→j′1j′2, which refer to collisions HF(j1)+HF(j2)+ΔE→HF(j′1) +HF(j′2), where ΔE is the energy gap. Particularly large cross sections are obtained for the j j+1→j+1 j transitions, which are both resonant and coupled to first order by the dipole–dipole interaction. The relationship between the calculated cross sections and the results of molecular beam scattering experiments is discussed. Total differential scattering measurements for HF–HF collisions are also reported and compared with the calculated results.
Photochemistry of adsorbed molecules. V. Ultraviolet photodissociation of OCS on LiF(001)
Authors: Leggett K. , Polanyi J. C. , Young P. A.
Published: July 2002

Dynamical studies of the UV photochemistry of submonolayer coverages of OCS physisorbed on 116 K LiF(001) are presented. Following pulsed ultraviolet laser irradiation (λ 222 nm), translational energy and angular distributions were obtained for photolysis products by angle-resolved time-of-flight mass spectrometry. Photolysis of adsorbates gave rise to distributions which differed markedly from gas phase photodissociation. Energetic sulphur and CO fragments were detected for coverages ≥10−5 monolayers. The cross section for photolysis in the adsorbed state was enhanced 103–104× relative to the gas phase. The dynamics for these photoprocesses were found to vary with adsorbate coverage, indicative of a catalytic influence of the surface on the photochemistry.
The Lorentz–Lorenz relationship in the phase diagram of triethylamine and water. Application to the coexistence curve
Authors: Gastaud R. , Beysens D. , Zalczer G.
Published: July 2002

The refractive index (n) of the partially miscible mixture of triethylamine and water has been measured at various temperatures (T) and concentrations. The data have been fitted to an analytic function. By using existing density data, the validity of the Lorentz–Lorenz formula has been tested. The same discrepancies that are usually observed in liquids have been found (−0.4% on n, and −13% on dn/dT). No supplementary deviation has been detected in the vicinity of the critical point. These data have been used to obtain a precise determination of the coexistence curve.
P-type doubling in the infrared spectrum of NO–HF
Authors: Fawzy Wafaa M. , Fraser G. T. , Hougen J. T. , Pine A. S.
Published: July 2002

The HF stretching band of the NO–HF open-shell complex has been recorded using a molecular-beam optothermal spectrometer. The spectrum exhibits P-type doubling indicative of an unpaired electron spin coupled to the rotational angular momentum of a bent complex with substantially quenched electron orbital angular momentum. From B̄″=0.111 320(17) cm−1, and an off-axis angle for the NO of 30°, the zero-point center-of-mass separation is estimated to be 3.4396(3) Å. The HF frequency shift of 84 cm−1 indicates that the complex is hydrogen bonded, and the spectral intensities imply that the HF axis is aligned closely to the center-of-mass axis and the NO is off axis by 30±15°. The Renner–Teller-like orbital quenching parameter is somewhat larger than the spin–orbit constant in the free NO molecule and increases substantially upon vibrational excitation. The transitions in this band exhibit vibrational predissociation broadening of 200±40 MHz (FWHM), similar to that observed for a number of closed-shell hydrogen-bonded HF complexes.
Band structure of stationary emission spectra from a three-level molecule pumped by strong radiation fields
Authors: Ohtsuki Y. , Fujimura Y. , Lin S. H.
Published: July 2002

A theory of the emission spectrum from a multilevel molecular system pumped by strong resonant radiation fields based on the double space theory of the density matrix is developed. We are especially concerned with a three-level, one-laser system, and a three-level, two-laser system. It is shown that the band structure cannot always be estimated by the energy level structure of the dressed states. In fact, in both model systems, triplet structures of the emission spectra can be observed in the case where the magnitude of the molecule-field interaction is larger than that of the detuning. The characteristic features of the band structure are interpreted in terms of the dressed state picture based on analytically solvable models. Several numerical calculations are performed to show how the multiplet band structure in the emission spectrum is influenced by the detuning and the power of the pump field(s).
Quantum statistical weights for reorientational correlation functions in the nuclear magnetic resonance relaxation of methyl groups
Authors: Bull T. E.
Published: July 2002

Rotationally symmetric groups containing nuclei with nonzero spin often exhibit uniquely quantum mechanical properties. Symmetry requirements on the total wave function restrict the allowable combinations of electronic, vibrational, rotational, and nuclear spin wave functions. NMR relaxation depends on operators that act on both the nuclear spin and rotational wave functions. The interdependence of the wave functions produces quantum statistical weights in the rotational correlation functions that can differ from semiclassical or classical probability distributions. The quantum statistical weights for the reorientational correlation functions in NMR relaxation have been derived for A3 and AX3 systems of spin 1/2 nuclei and for deuterium relaxation in a deuterated methyl or equivalent group. It is found that classical weights apply to deuterium relaxation. The A3 system has distinctly nonclassical weights. And the AX3 system has eight sets of weights, with different weights applying to different types of correlation functions. One of the eight is the classical weight, and two of the sets can lead to terms that do not arise in the usual, semiclassical theory. It is shown that, under certain circumstances, the predictions of this quantum mechanical theory differ from those of the semiclassical model. The present theory also predicts that changing the symmetry of the electronic/vibrational states can alter the NMR relaxation behavior. Calculations with a stochastic quantum dynamical model indicate that these differences may be experimentally important for, among other things, relaxation involving a methyl group in a biomolecule at physiological temperatures.
Structure factor of X4 tetrahedral molecular liquids: Competition between intramolecular and intermolecular atomic spacings
Authors: Misawa M.
Published: July 2002

Structure factor Sm(Q) of liquids of simple tetrahedral molecules X4 has been calculated as a function of ζ, where ζ is a ratio of the intermolecular atomic spacing L to the intramolecular atomic spacing l, i.e., ζ=L/l, under constraints of a fixed preferred orientation between the nearest neighbors and a fixed packing fraction of uncorrelated molecules. It turned out that the Sm(Q) depends strongly on the ratio ζ. An important feature of the calculated Sm(Q)’s is an appearance of a new peak at low Q region and its rapid growth with increasing ζ. The characteristic features of the experimental Sm(Q)’s of liquids P4 and VCl4 can be reasonably reproduced by the present simple calculation with ζ=1.64 for liquid P4 and 1.14 for liquid VCl4. These values of ζ are simply interpreted by the molecular size and intramolecular atomic spacing of each molecule.
Thermal kinetics in small systems. III. Isotopic effects
Authors: Klots Cornelius E.
Published: July 2002

We consider here kinetic isotope effects in small systems excited to some common energy as measured from their respective zero points. A transparent and model-free expression is derived relating these effects to their counterparts in a heat bath. The expression affords an immediate understanding of the origin of these effects. Its use is illustrated by application to the dissociation of benzene and substituted-benzene cations.
Comment on: Deuterium nuclear fusion at room temperature: A pertinent inequality on barrier penetration
Authors: Morgan John D.
Published: July 2002

Gerald Rosen (Ref. 1) claims to justify the large value apparently observed by Fleischman and Pons and also by Jones et al., in their experiments on cold fusion. Rosen derives an inequality for the Coulomb barrier penetration factor. This comment points out a crucial error in his derivation. (AIP)
Determination of the spherically symmetric potential components for Li+–N2 and Li+–CO from total cross section measurements
Authors: Gislason Eric A. , Polak-Dingels Penny , Rajan Malini S.
Published: July 2002

Total cross sections have been measured for Li+ ions scattered by N2 and CO in the range EΘR=5–1000 eV deg. Here E is the lab energy of the Li+ beam, and ΘR is the resolution angle of the apparatus. From the data the spherically symmetric parts of the intermolecular potentials have been determined over a wide range of Li+-molecule distances including the attractive well region. The results are compared with other theoretical and experimental work on these systems.
Steady, elongational flow of dilute solutions of once-bent, once-broken, and deformable rod polymers
Authors: Jorquera Hector , Qin Lihong , Dahler John S. , Lee Jang-oo
Published: July 2002

Calculations have been made for steady–state elongational flows of dilute solutions of polymer molecules modelled as rods decorated with beads that interact frictionally with the solvent. The models are chosen to mimic structural and dynamic features of real polymer molecules. In one model, the rods are rigid and bent at one point. In another, they are broken into two parts and then hinged together. The third model is a flexible rod that forms a circular arc with a variable radius of curvature. The elongational (Trouton) viscosity and the flow birefringence have been calculated as functions of the model parameters. Numerical results are presented for a large range of deformation rates.
Ru3(CO)12 interaction with Ru(001) and Au/Ru surfaces
Authors: Malik Igor J. , Hrbek Jan
Published: July 2002

We studied the interaction of Ru3(CO)12 with a Ru(001) surface and with Ru(001) covered with approximately 2 monolayers of Au(Au/Ru). We report IRAS (infrared reflection–absorption spectroscopy) and TDS (thermal desorption spectroscopy) results for Ru3(CO)12 adsorbed at these surfaces at coverages between ∼0.2 monolayer (θRC∼0.2) and θRC∼10. IRAS spectra show sharp bands (FWHM∼4 cm−1) for Ru3(CO)12/Ru(001) at all studied coverages and for Ru3(CO)12/Au/Ru at θRC >3. IRAS results imply well-ordered adsorbate layers with the Ru3-triangle of Ru3(CO)12 parallel to the surface. Infrared spectra of Ru3(CO)12/Au/Ru at θRC <∼3 show broadening and splitting of the absorption bands. TDS results suggest a molecular adsorption of Ru3(CO)12 for coverages giving sharp IRAS bands and a possible fragmentation of Ru3(CO)12 at Au/Ru at low coverages.
Single-crystal electron paramagnetic resonance study of triplet excitons in [Fe(mesitylene)2+2][C3(C(CN)2)−3]2
Authors: Morton J. R. , Preston K. F. , Le Page Y. , Williams A. J. , Ward M. D.
Published: July 2002

Single crystals of [Fe(mesitylene)2+2][C3(C(CN)2)−3]2 exhibit an intense EPR spectrum with anisotropy and fine structure typical of an electronic triplet species (S=1). From measurements of the fine-structure splitting as a function of angle in three orthogonal crystal planes, it has been established that the spin–spin interaction tensor is nearly axial, D=(−218, 116, 105 MHz), and that the g tensor is almost isotropic with giso =2.0027. The zero-field splitting parameters were determined as ‖D‖=327.8 MHz (117 G) and ‖E‖=5.7 MHz (2 G). Comparison of the principal directions of D with vectors within the known crystal structure shows that the triplet comprises a radical pair formed between nearest neighboring anions. The principal values and directions of D for the biradical compare well with those calculated for the unpaired spin density distribution deduced for the monoradical from its isotropic spectrum and from INDO calculations.
Study of the integrated intensity of depolarized light scattering spectra of tetrahedral molecules
Authors: Friedrich Valerie , Tarjus Gilles , Kivelson Daniel
Published: July 2002

We have investigated, both experimentally and theoretically and as a function of both temperature and pressure, the integrated intensity IVH of the depolarized light scattering of liquids and liquid mixtures composed of tetrahedral molecules. The major contribution to IVH arises from dipole-induced–dipole interactions, and the marked decreases of (IVH/ρ2) with small changes of density ρ is attributed to significant increases in the symmetry of the local molecular environment of a given molecule, perhaps an increase associated with ‘‘interlocking structures’’ or ‘‘meshing of gears.’’ We believe IVH/ρ2, because of its sensitivity to the placement of all near neighbors of a molecule, may be a useful probe of local structure, particularly for tetrahedral molecules.
The two-state model applied to high pressure mobility results for 2,2,4-trimethylpentane
Authors: Berlin Y. A. , Holroyd R. A.
Published: July 2002

The behavior of the electron mobility in 2,2,4-trimethylpentane at high pressure is analyzed in the framework of the two-state model of electron transport. The increase in mobility at 22.5°, as the pressure increases, is shown to be correlated with an increase in μF, the free state mobility. The probability of localization first decreases slightly then increases slightly with pressure. Although both the conduction band energy V0 and the trapped state energy Et increase with pressure, the difference V0 − Et is shown to remain constant.
Configuration dependent crossed beam reactive scattering in an intense laser field
Authors: Grubbs Robert K. , Eno Larry
Published: July 2002

We model the reaction between crossed beams of atoms A and diatoms BC in an intense nonresonant laser field. Cross sections are in particular determined for laser switching between a pair of one-dimensional potential curves which are free to rotate in space. The cross sections are dependent on the configuration or orientation of the laser field with respect to the initial relative velocity vector of the reactants; for computational simplicity, many of our calculations are performed for coincident field and relative velocity vectors. Contributions to the cross sections arising from interference between the phases of transition matrix elements, are highlighted by comparing with ones determined by random phase approximation. We also make comparison with the corresponding configuration averaged (and phase independent) cross section. Photon energy dependencies for the various cross sections are obtained at several field intensities and collision energies. We find that the shifting with photon and collision energy, of the range of partial waves from which a cross section draws, can dramatically affect the relationship between phase dependent and independent cross sections; the shifting modifies in particular the interference between transition elements. For a single field intensity and photon and collision energy, we also generate cross sections as a function of configuration angle. The structure of the configuration dependence is elucidated by decomposition into terms which are characterized by numbers of contributing photons.