bluuebunny/crossref_metadata_2025 huggingface dataset:
On the equation of state of argon and organic liquids
Authors: Jain R. K. , Simha Robert
Published: February 2003

The results of a statistical theory oriented towards and extensively applied to chain molecular fluids are further examined, with a twofold purpose in mind: First, in order to explore the validity of the theory for monomer-type liquids. Secondly, to examine the behavior of the parameter 3c, the number of effectively external degrees of freedom per molecule, in instances where a priori assignments of this number may be feasible. The agreement between experimental and theoretical isotherms and isobars is satisfactory over a wide range of temperatures and pressures for the three typical systems investigated, viz., argon, carbon tetrachloride, and benzene. It is noteworthy in this connection, that the linear relation between 1nV and T3/2 at atmospheric pressure observed earlier, retains its validity for the organic liquids. As for the numerical values of c, they turn out to be smaller than anticipated.
General kinetic models of activated processes in condensed phases
Authors: Skinner James L. , Wolynes Peter G.
Published: February 2003

We continue our study of chemical relaxation processes [J. Chem. Phys. 69, 2143 (1978)] in considering a classical particle in a one-dimensional bistable potential coupled to a heat bath environment. We introduce a class of kinetic models which subsumes the special cases of the Rayleigh–Fokker–Planck, BGK, and Lorentz models. Using both analytical and numerical techniques we calculate the chemical relaxation rate of this system for different kinetic models and coupling strengths. We find that except in the Rayleigh limit, for a small range of couplings, transition state theory is quantitatively a poor approximation. Transition state theory is particularly inaccurate in the Lorentz limit, where it overestimates the rate by a factor of ten or more for all values of the coupling.
Theory of dynamic depolarized light scattering from nonrigid polymer chains. II. Freely rotating chains
Authors: Moro Keiji , Pecora R.
Published: February 2003

The depolarized light scattering spectrum from a dynamic, freely rotating chain model of a macromolecule is calculated. The previous theory is improved to include a chain stiffness parameter which is related to the persistence length of the polymer chain and hence can be measured by other experimental techniques. In the flexible limit of the model the results reduce to those by Ono and Okano for the Rouse–Zimm model. For intermediate degrees of chain stiffness the contribution from the lowest mode to the scattering intensity is enhanced.
Pyrolysis of ethylamine. II. Synthesis and microwave spectrum of ethylidenimine (CH3CH=NH)
Authors: Lovas Frank J. , Suenram Richard D. , Johnson Donald R. , Clark Frank O. , Tiemann Eberhard
Published: February 2003

Microwave rotational spectra assignable to gas phase cis- and trans-ethylidenimine (CH3CH=NH) have been detected in the pyrolysis decomposition products from several alkylamines and from the ring trimer, (CH3CHNH)3. Stark effects, hyperfine and internal rotation splittings have aided the assignment of the observed spectra and allowed the determination of rotational distortion constants, 14N nuclear electric quadrupole coupling constants, internal rotation barriers, and electric dipole moments. Limited structural information was also obtained.
Excited state absorption spectra and intersystem crossing kinetics in diazanaphthalenes
Authors: Scott Gary W. , Talley Larry D. , Anderson Robert W.
Published: February 2003

Picosecond time-resolved, excited state absorption spectra in the visible following excitation at 355 nm are discussed for room temperature solutions of four diazanaphthalenes (DN)—quinoxaline (1,4-DN), quinazoline (1,3-DN), cinnoline (1,2-DN), and phthalazine (2,3-DN). Kinetics of singlet state decay are obtained by monitoring the decay of Sn←S1 bands. The intersystem crossing rate constant (kisc) is found to vary as kisc(1,4-DN)≳kisc(1,3-DN)≳kisc(1,2-DN). The kisc in phthalazine could not be determined from the weak, visible Sn←S1 absorption. Assuming rapid singlet vibrational relaxation and only minor effects due to energy gap variations, these experimental results agree with statistical limit predictions for the relative nonradiative rate. Calculations of the spin–orbit coupling matrix element βel= 〈S1(1nπ*)‖ ℋso ‖ T1(3ππ*)〉, using INDO wave functions, give the ordering βel(1,4-DN)≳βel(2,3-DN)≳βel(1,3-DN) ≳βel(1,2-DN).
Density and temperature effects on vibrational phase relaxation and frequency shifts in liquid isobutylene
Authors: Schindler Wolfgang , Jonas Jiri
Published: February 2003

The Raman line shapes of the ν4 (A1) symmetric C=CH2 stretching mode at 1657 cm−1 and the ν9 (A1) symmetric C–CH3 stretching mode at 805 cm−1 in isobutylene have been measured as a function of pressure from vapor pressure densities to 0.8 g cm−3 over the temperature range from −25 °C to 75 °C. The frequency shifts of the above isotropic bands have also been determined under the same experimental conditions. The important experimental finding is the opposite effect of density on the isotropic linewidths of the C–CH3 and C=CH2 stretching vibrations; namely, the former band broadens with increasing density whereas the latter band narrows with increasing density under isothermal conditions. Such narrowing is unexpected in view of the theoretical and experimental results on the mechanism of vibrational broadening. A very different behavior is also observed for the frequency shifts of these two stretching modes. There is a large red gas-to-liquid shift for the C=CH2 band while its frequency changes very little with density over the liquid range studied. The opposite is true for the C–CH3 band which has a small gas-to-liquid shift but exhibits a large blue shift with increasing density in the liquid region. A qualitative interpretation of the experimental frequency data is based on consideration of classical vibrational amplitudes of the two vibrations and the infrared activity of the C=CH2 mode. The experimental vibrational widths are discussed in terms of available theoretical models for dephasing and other mechanisms for broadening of isotropic Raman line shapes. It appears that the behavior of the C–CH3 band can be best interpreted considering the isolated binary collision model for dephasing and additional energy relaxation, whereas the unusual density effects on the linewidth of the C=CH2 band are discussed in a more general way using the Kubo stochastic line shape theory.
The effect of α-hydroxyacetamide upon the formation of an alkoxy radical in α-chloroacetamide single crystals: An ESR study
Authors: Dickinson A. C. , McMurray V. , Kispert L. D.
Published: February 2003

The inclusion of 0.05 to 20 mol% of α-hydroxyacetamide in single crystals of α-chloroacetamide has shown that the four line ESR pattern observed for x-ray irradiated α-chloroacetamide single crystals at 77 K is due to the alkoxy radical ⋅OCH2CONH2. The intensity of the four line ESR pattern is proportional to the concentration of α-hydroxyacetamide up to 1 mol% at which point it levels off and then decreases above 5 mol%. The alkoxy radical is not observed in pure α-hydroxyacetamide crystals.
Tandem quadrupole study of laser photodissociation of CO−3
Authors: Hiller J. F. , Vestal M. L.
Published: February 2003

Absolute cross sections for the production of O− by photodissociation of CO−3 have been determined at intervals of 1 nm or less throughout the range from 400 to 635 nm using a tandem quadrupole mass spectrometer equipped with a tunable dye laser. In addtion, the dependence of the apparent photodissociation cross section on ion source pressure, laser polarization, laser intensity, ion lens voltage, and pressure of CO2 in the photon–ion interaction region has been studied at selected wavelengths. The threshold for photodissociation of ground state CO−3 is found to be 2.258±0.008 eV in excellent agreement with a recent indirect determination of a lower limit for D(CO2–O−) of 2.27 eV, but in disagreement with earlier photodissociation results. Studies of collisional enhanced dissociation of laser excited ions indicate that only a fraction of the ions excited between threshold and 2.6 eV dissociate unimolecularly within 50 microsecond observation time. Below 2.2 eV, two photon dissociation of CO−3 is observed, and at 581 nm (2.13 eV) saturation of one of the transitions involved is observed, indicating a photoexcitation cross section of ca. 4×10−17 cm2. A model based on these observations is proposed which appears to account for the apparent disagreement between our results and earlier laser photodissociation work.
Strong, positive-ion hydrogen bonds: The binary complexes formed from NH3, OH2, FH, PH3, SH2, and ClH
Authors: Desmeules Peter J. , Allen Leland C.
Published: February 2003

A systematic, ab initio electronic structure analysis of the strong, positive-ion hydrogen bond is reported. Energies and wave functions have been obtained at the 4-31G level for the twenty-one complexes, (B⋅⋅⋅H–A)+, where A,B=NH3, OH2, FH, PH3, SH2, ClH. The A–H bond length (r1), the B⋅⋅⋅A separation (R(, and the angle (ϑ) measured relative to the symmetry axis of B have been optimized. Calculated dimerization energies ED are found to be in reasonable agreement with experiment. Charge density difference plots of these complexes exhibit a remarkable similarity to the pattern of alternating charge gain and loss known for the neutral H-bonded dimers. The proton donor is characterized by a charge gain region between A and the proton and charge loss on the proton; the electron donor by a charge loss between B and the proton. Four of the complexes (HF⋅⋅⋅H⋅⋅⋅FH)+, (H2O⋅⋅⋅H⋅⋅⋅OH2)+, (HCl⋅⋅⋅H⋅⋅⋅ClH)+, (HCl⋅⋅⋅H⋅⋅⋅FH)+, have unusually short internuclear separations and show large charge gain around the protons. This is the first theoretical evidence of a transition from predominantly electrostatic to predominantly covalent binding in hydrogen bonding and it corroborates a recent experimental X–N study. An estimate of the amount of charge lost from the proton, ΔqH, has been obtained from the difference plots and is found to bear a linear relation with the dimerization energy ED for a series of complexes with a single proton donor. The inverse relation between ED and the difference in monomer proton affinities, ΔPA, reported in the literature for substituted pyridinium ions, is shown to hold as well for all A and B. Our calculated results also give a quantitative demonstration of the recently proposed inverse relationship between proton position and ΔPA. Several useful new organizing principles have been found: (a) R varies linearly with r2, the B⋅⋅⋅H distance. Covalent bonding in the four complexes noted above is indicated by deviation from this line. Crystal structures taken from the literature also obey this relationship and the satisfactory agreement between experiment and calculations show that the 4-31G basis is adequate for predicting strong H-bond geometries. (b) RN/R?1.2, where RN is the A⋅⋅⋅B separation in neutral hydrogen bonds. (c) ED displays a smooth inverse relation to r2 for a sequence of complexes with a single electron donor.
Dynamics of fluctuations and spinodal decomposition in polymer blends
Authors: de Gennes P. G.
Published: February 2003

We discuss here some qualitative features of the concentration fluctuations in binary polymer melts A+B, A and B being long, flexible chains, with a Flory interaction parameter χ which can be positive (favoring segregation), or negative. In the one phase domain, the fluctuations of long wavelength (2π/q) are expected to relax by a reptation process. At shorter wavelengths (qR0≳1, where R0 is the size of one chain) equilibration takes place by local adjustment of each chain inside a fixed ’’tube’’: the predicted relaxation rates τq−1 are proportional to q6 for χ?0. (For a negative χ, opposing segregation, one expects τq−1∼q4). In the two phase domain, where the trend towards segregation is strong (χN≫1, N being the number of monomers per chain), one should observe a very anomalous type of spinodal decomposition: in the early stages, the growing fluctuations have a wavelength comparable to the thickness of the interfacial region, and small compared with R0: the growth is realized through local adjustment. During the later stages (Ostwald ripening) the size R(t) of the growing droplets should change from a t1/5 behavior (when R≲R0) to a t1/3 behavior (in the classical limit R≳R0).
Studies of rotational predissociation of van der Waals molecule by the method of complex coordinate
Authors: Chu Shih-I
Published: February 2003

A practical method is presented for calculating resonance energies and widths (lifetimes) of metastable states of van der Waals molecules, incorporating the use of complex coordinate transformation and square-integrable basis functions. The utility of the method is illustrated through a study of the level widths and energies of rotationally predissociating atom–diatom model systems. Satisfactory agreement with previous works was found. Besides involving only bound state calculations and being free from imposement of boundary conditions, the method can be readily extendable to multichannel coupling problems.
A theory of homogeneous condensation from small nuclei. I. Modified Mayer theory of physical clusters
Authors: Lockett A. M.
Published: February 2003

A theory of physical clusters is developed within the framework of the Theory of Imperfect Gases. Physical monomers and clusters are redefined diagrammatically thereby removing the unphysical nature of the usual Mayer clusters while retaining essentially all of the desirable features of the Mayer theory. The resulting formulation is simple, unambiguous, and well suited for incorporation into a kinetic theory of condensation which is computationally tractable.
Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Ru–Cu clusters
Authors: Sinfelt J. H. , Via G. H. , Lytle F. W.
Published: February 2003

A study was made of the extended x-ray absorption fine structure (EXAFS) associated with the K absorption edges of ruthenium and copper in a silica supported ruthenium–copper catalyst containing 1.0 wt.% ruthenium and 0.63 wt.% copper (1:1 atomic ratio of ruthenium to copper). Previous chemisorption and catalysis studies indicated a strong interaction between the ruthenium and copper in the catalyst, and led to the suggestion that the catalyst consisted of bimetallic clusters of ruthenium and copper dispersed on the silica. The EXAFS data of this investigation provide information on the structure of the ruthenium–copper clusters. The ruthenium in the bimetallic clusters appears to be very similar to the ruthenium in a silica supported ruthenium reference catalyst, in that the ruthenium atoms are coordinated predominantly to other ruthenium atoms and only to a minor extent to copper atoms. By contrast, the copper atoms in the clusters have nearest neighbors which are more nearly equally distributed among copper and ruthenium atoms. The results are consistent with a model of a ruthenium–copper cluster in which the copper is present at the surface.
An ESR study of an α-bromofluoro π-radical: Determination of the relative signs of the hyperfine and quadrupole couplings
Authors: Muto H. , Kispert L. D.
Published: February 2003

An ESR study has been carried out for the bromofluoro alkyl π-radical, ĊBrFCOOH, trapped in x-ray irradiated bromofluoroacetic acid crystals. Strong forbidden transitions, especially ΔMBr=±2 transitions are observed and it has been possible to determine the relative signs of the principal components of the α-bromine hyperfine 𝒜 and quadrupole 𝒬 tensors. Analysis shows that these signs are different from those previously assumed. The principal values obtained were equal to 𝒜 = ( + 108, + 39, + 22)±7 G, and 𝒬 = ( – 13, + 18, –5)±2 G for 81Br and 𝒜 = (196, 20, 0) G for 19F. The nature of the chemical bond and the geometry of the radical have been deduced from these tensors.
Molecular beam study of the Cu+F2 chemiluminescent reactions
Authors: Schwenz R. W. , Parson J. M.
Published: February 2003

Chemiluminescence of CuF formed in the reaction of ground state Cu and F2 has been studied using a molecular beam–scattering gas arrangement. Relative rates for forming the A, B, and C states of CuF were determined, and an inversion of population is observed for the C relative to the B state. Computer simulations of the observed spectra have provided information on the vibrational and rotational distributions in the excited CuF states. Simulation of the B and C spectra is straightforward, but the A state must include 1Σ and 1Π parts of a p complex, as well as corrections for diffusion from the observation region. Average fractions of energy available disposed in vibration are 0.30, 0.34, and 0.29–0.38 for the C, B, and A states, respectively. Average fractions disposed in rotation for the same three states are 0.21, 0.20, and 0.21–0.22. These fractions correspond closely to prior expectations based on product densities for vibration, but are much less than prior expectations for rotation. Weak emission is also observed from the a(3Σ) state with average vibrational energy close to prior expectations.
Perturbation theory and the thermodynamic properties of fluids. III. Inverse-power and 6–12 potentials
Authors: Kerley Gerald I.
Published: February 2003

This paper is the last of three articles describing a hard sphere perturbation theory of liquids and dense gases. The CRIS model, derived in the preceding papers, is tested by applying it to fluids having inverse-power and 6–12 potentials. Thermodynamic properties, radial distribution functions, and the vapor–liquid coexistence curve are calculated and compared with computer simulation results. Agreement is very good.
Experimental studies of nucleation in near-critical liquid mixtures
Authors: Howland Rebekah G. , Wong Ning-Chih , Knobler Charles M.
Published: February 2003

Cloud-point measurements have been performed on the mixtures isobutyric acid + water and perfluoromethylcyclohexane + methylcyclohexane in the neighborhood of their critical solution temperatures. The stability limit is in accord with classical nucleation theory for values of the reduced temperature ε = (Tc−T)/Tc greater than about 10−4 but rises sharply as the critical point is approached. Interfacial tension measurements on both mixtures are also reported.
Analysis of the spin-Hamiltonian parameters for Eu2+ in the alkali halides
Authors: Rubio O. J. , Ruíz-Mejía C. , Oseguera V. U. , Murrieta S. H.
Published: February 2003

An analysis is made, in terms of the superposition model, of the second- and fourth-order spin-Hamiltonian parameters for the Eu2+ ion in orthorhombic C2v symmetry sites of the alkali halides. Values for the intrinsic parameters b̄2 and b̄4 and for the power law exponents t2 and t4 are reported for the divalent europium ion surrounded by fluorine, chlorine, bromine, and iodine ions as ligands. It is found that the b̄4 value of Eu2+ decreases as the polarizability of the ligand increases in agreement with the results previously reported for the isomorphic Gd3+ ion and for the transition metal ions Mn2+ and Fe3+. It is established, for the first time, that the value for the intrinsic parameter b̄2 of Eu2+ also decreases as the polarizability of the ligand increases. In order to carry out the analysis mentioned above, a theoretical calculation was made of the lattice distortion around the impurity ion caused by its substitution for the host alkali ion in all the alkali halides.
Magnetic field effects in the infrared multiphoton dissociation of CF2HCl
Authors: Duperrex R. , van den Bergh H.
Published: February 2003

The application of 14 kG magnetic field greatly increased the multiphoton dissociation yield of CF2HCl. This effect is attributed to the breakdown of angular momentum selection rules. (AIP)
Relaxational compressibility in liquid water
Authors: Endo Harumi
Published: February 2003

The relaxational compressibility of water is discussed. The comments by the author on the results of Slie et al. are regarded erroneous and good agreement is obtained between present calculations and Ref. 3 results. (AIP)
Binding energies of the Eu2+ cation vacancy complexes
Authors: Ruíz-Mejía C. , Oseguera V. U. , Murrieta S. H. , Rubio O. J.
Published: February 2003

Values for the binding energy of the ground and first excited states of the impurity Eu2+–cation vacancy pair are reported for the alkali halides.
Theoretical study of C2 and C2−
Authors: Dupuis M. , Liu B.
Published: February 2003

Potential energy curves of the ground states of C2(X 1Σg+) and C2−(X 2Σg+) have been calculated using SCF, MCSCF, and CI methods. Close agreement with experimental dissociation energies, bond lengths, and spectroscopic constants is obtained by a CI calculation including all single and double excitations from the restricted Hartree–Fock configuration, with corrections for the quadrupole excitations estimated by a formula due to Davidson. The restricted Hartree–Fock method overestimates the electron affinity of C2, giving a value 4.33±0.02 eV to be compared with the experimental value of 3.54±0.05 eV. The effect of higher excitations on calculated electron affinity has been investigated, and some general conclusions regarding the computation of molecular electron affinity have been drawn.
The ‘‘primitive’’ wave function in the theory of intermolecular interactions
Authors: Kutzelnigg Werner
Published: February 2003

The concept of the primitive wave function for a supermolecule consisting of interacting subsystems is critically analyzed. The distinction between formal and genuine primitive functions is stressed. The concept of uniformly complete basis sets as contrasted to simply complete basis is introduced. Primitive basis sets are defined and shown not to be uniformly complete for the expansion of the supersystem wave function while ’full supersystem basis sets’ are. The conditions are specified under which a supersystem wave function can be decomposed into its ’primitive components’ corresponding to different partitions of the electrons among the subsystems. These primitive components satisfy the Schrödinger equation asymptotically. The matrix representation of the Hamiltonian (both the full supersystem Hamiltonian H and the zeroth order Hamiltonian Ho) in terms of these partitions is analyzed. It is shown that in the standard application of RS-perturbation theory to intermolecular forces (the polarization approximation) the limiting processes λ→1 and R→∞ do not commute, that the λ-series is not uniformly convergent with respect to R and that the wave function to any finite order in λ is genuinely primitive. The symmetrized polarization approximation is justified for the ’coasymptotic ground state’ in certain cases and a ’symmetrized polarization approximation with shifted eigenvalues’ is proposed that connects the lowest eigenvalue of Ho with the physical ground state. A justification of simplified schemes in the region of ’small exchange’ is given and alternative perturbation schemes are discussed. Finally the use of the primitive function in variational treatments is outlined. One advantage is that a genuinely (not a formally) primitive function is uniformly expandable in a primitive basis set.
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o effective core potentials including relativistic effects. V. SCF calculations with ω–ω coupling including results for Au2+, TlH, PbS, and PbSe
Authors: Lee Yoon S. , Ermler Walter C. , Pitzer Kenneth S.
Published: February 2003

A b initio self-consistent field calculations are reported for a series of diatomic molecules using relativistic effective core potentials (REP) and basis sets appropriate for ω–ω coupling. The molecular orbitals are expressed as linear combinations of two-component analogs of Dirac spinors. The unique feature of the present approach is the retention of the spin–orbit operator in the generation of the REP’s and the propagation of its effects into the molecular wave functions in a totally consistent fashion. The nature of bonding in the molecules Au2+, TlH, PbSe, and PbS is discussed with consideration of the orbital energies, spectroscopic constants, and population analyses. Comparisons with recently obtained photoelectron spectra of PbSe and PbS are made. It is noted that 6p1/2 and 6p3/2 orbitals exhibits bonding characteristics that are different from the nonrelativistic pσ and pπ molecular orbitals.
General second order MCSCF theory: A density matrix directed algorithm
Authors: Lengsfield Byron H.
Published: February 2003

A quadratically convergent general MCSCF algorithm is presented which is suitable for both ground state and excited state calculations. This method converges more rapidly than annihilation of singles techniques and is computationally very attractive as it does not involve the contraction of a potentially large Hamiltonian matrix on each interation. Sample calculations are performed on the two lowest states of the same symmetry for Li2, Li4, and BeO. For BeO, a symmetry restricted full valence MCSCF (81 configuration state functions) and a first order CI calculation using the MCSCF orbitals yielded good agreement with the experimental splitting of the two lowest 1Σ+ states. The results demonstrate that the algorithm described is capable of providing an efficient solution of large, general, MCSCF problems.
Laser fluorescence studies of metal clusters: Spectroscopy of molecular bismuth
Authors: Bondybey V. E. , English J. H.
Published: February 2003

The electronic spectra of Bin clusters in solid Ne and Ar matrices are studied by absorption and laser induced fluorescence techniques. The Bi2 ?→? spectrum appears to be unperturbed by the solid medium. A second, slightly lower lying excited electronic state may also be due to Bi2. Spectra belonging to another bismuth cluster, most likely to Bi4 are also observed and analyzed. The vibrational frequencies of the emitting species are determined. The spectrum is consistent with a Td structure for the tetramer, but shows no evidence of Jahn–Teller distortions.
Perturbation theory and the thermodynamic properties of fluids. II. The CRIS model
Authors: Kerley Gerald I.
Published: February 2003

This paper is the second of three articles describing a hard sphere perturbation theory of liquids and dense gases. The general theory presented in the preceding paper is used to derive a model for calculating thermodynamic properties. Three approximations are made. First, we assume that each molecule is located at the center of a spherical shell formed by its neighbors. The radius of this shell varies throughout the fluid according to a distribution function which is known for hard spheres. Second, the coordination number varies along with the nearest neighbor distance in such a way that the volume per molecule is constant and equal to the macroscopic value. Third, the potential energy of a molecule in the field of its neighbors depends only on the nearest neighbor distance and coordination number. Using this approximation, the energy of a liquid molecule can be calculated from the zero-temperature isotherm of the solid at the same nearest neighbor distance. There are no adjustable parameters in the theory. All that is needed to apply the model is the cold curve of the solid, which can be obtained from either theory or experiment.
Vibrational emission by HCl from the ClF–H2 chemical laser
Authors: Pimentel George C. , Krogh Ole D.
Published: February 2003

The zero-gain and equal-gain temperature methods have been used to measure vibrational rate-constant ratios for the reaction: H+ClF→HCl+F: N1/N0=3.5±0.8, N2/N1=2.3±0.3 and N3/N2=0.9±.2. These data are in accord with relative rate constant measurements obtained through chemiluminescence studies. Furthermore, they provide the first information about k0 and they narrow considerably the uncertainty range for k1. Combining all of the available data, a ’’best’’ value of the fraction of available energy into vibration, fv=0.40, is obtained. With the complete set of vibrational rate constants, a linear surprisal plot can be obtained by assuming that only a portion of the energy released is ’’available’’ for vibrational excitation. It is suggested that this portion measures the energy released in the reaction entry channel, Polanyi’s ’’attractive energy release.’’ This interpretation is consistent with the results of similar treatments of the rate constant data for the H+X2 reactions (X=F, Cl, Br).
Effects of vibronic interaction and autoionization on the photoelectron spectrum of N2O
Authors: Dehmer P. M. , Dehmer J. L. , Chupka W. A.
Published: February 2003

High-resolution and high-sensitivity HeI photoelectron spectra (PES) are reported for the first four valence levels of N2O. The vibrational structure, including many new peaks, is completely assigned for the X 2Π, A 2Σ+, and C 2Σ+ electronic states, and in all three cases excitation of a single quantum of the bending vibration is observed. The bending mode appears as a result of vibronic coupling within and between different electronic states. The Renner–Teller splitting is resolved in the (0,1,0) band of the transition to the X 2Π state. The relative intensities of the vibrational bands in the X 2Π and A 2Σ+ states are compared to the intensities determined from the threshold photoelectron spectra (TPES) of Frey et al. [Chem. Phys. Lett. 54, 411 (1978)]. In both states, autoionization of intermediate neutral states that are nearly degenerate with the molecular ion state to which they decay increases the relative intensities of the higher vibrational bands in the TPES. This resonant autoionization process can enhance bands selectively, and, in particular, the higher quanta of the symmetric stretch are systematically more intense in the TPES than in the HeI PES. New relative photoionization cross sections for N2O and its fragment ions are presented which show that even weak autoionization features can have a substantial effect on the intensities in the TPES.
On the blue phase of cholesterogenic liquid crystals. A deuterium NMR study
Authors: Samulski E. T. , Luz Z.
Published: February 2003

Deuterium NMR measurements of cholesterogenic systems exhibiting the blue phase are reported. The measurements were performed on specifically deuterated cholesteryl nonanoate (CN) and cholesteryl myristate (CM) as well as on deuterated probe molecules dissolved in normal CN and CM. The blue phase exhibits NMR spectra that are distinctly different from both those of the cholesteric and isotropic phases. The spectral line shape is consistent with the following model for the blue phase: It is a liquid crystal made up of cholestericlike chiral segments whose elementary units are arranged in a cubic symmetry. The dimension of the elementary units are of the order of the cholesteric-phase pitch length, i.e., several thousand angstroms. Translational diffusion of molecules along or between the chiral segments results in reorientational fluctuations of the director, which in turn affects the NMR line shape. The correlation times for the director reorientation calculated from this model and estimated translational diffusion coefficient for the various probe molecules are in excellent agreement with those derived from the experimental NMR line shape.
Charge transfer coefficients for the O+(2D)+N2 and O+(2D)+O2 excited ion reactions at thermal energy
Authors: Johnsen Rainer , Biondi Manfred A.
Published: February 2003

The reactions of metastable O+ ions with N2 and O2 have been investigated using drift tube-mass spectrometer techniques. It is found that ordinary charge transfer is the dominant reaction branch in both cases, occurring with large rate coefficients, k(N2) = (8±2)×10−10 cm3/sec and k(O2) = (7±2)×10−10 cm3/sec, at an effective ion temperature of ∼550 K. The reaction He++O2 is used as a source of metastable O+ ions, and evidence is presented that the O+ ions so produced are in the 2D state rather than the 2P state. The results are compared with previous measurements and inferences drawn from ionospheric observations.
Classical model for laser-induced nonadiabatic collision processes
Authors: Orel Ann E. , Miller William H.
Published: February 2003

By synthesizing earlier work of Orel and Miller and of Meyer, McCurdy, and Miller, a model for describing laser-induced electronically nonadiabatic collision processes is constructed which treats all degrees of freedom—heavy particle (i.e., translation, rotation, and vibration) electronic, and photon—by classical mechanics. This then makes it relatively easy to carry out calculations to simulate such processes within a dynamically consistent framework. Application is made to the test case H+LiF→Li+HF reaction considered by Light and Altenberger-Siczek. The most interesting feature revealed by these classical calculations is maxima in the reaction probability as a function of initial translational energy at energies below the laser-free threshold. It is seen that this structure can be understood as a Franck–Condon-like effect.
Self-shifting of CO2 lines in the 3ν3 band at 1.43 μm
Authors: Arcas Ph. , Arié E. , Boulet C. , Maillard J. P.
Published: February 2003

Pressure induced shifts have been observed in 3ν3 band of pure CO2, with the high resolution Fourier transform spectrometer of Meudon and using a ’’single beam two cells’’ method. It is shown that these shifts originate mainly from a vibrational effect connected to the anharmonic nature of the vibrational states of CO2. (AIP)
Rational fraction representation of diatomic vibrational potentials. II. Application to H2 ground state
Authors: Beckel Charles L. , Kwong Robin B. , Hashemi-Attar Ali-Reza
Published: February 2003

Representation by rational fraction [L/N] is applied to the Born–Oppenheimer potential V for the H2 ground electronic state. Here L and N are the degrees of numerator and denominator polynomials, respectively, in nuclear separation R. To yield the long range form of V, N is restricted to L+6. A [5/11] fitting has an rms error from Kol/os and Wolniewicz’ V of 0.43×10−7 hartrees on 0.7⩽R⩽12 Bohr radii. This [5/11] extrapolates well above R=12. It has a pole at 1.9×10−4 a.u. with residue 0.98, close to the correct values 0 and 1, respectively.
Phase transition in octomers of ice
Authors: David Carl W.
Published: February 2003

The thermodynamic energy of the octomer of ice is computed using standard Monte CArlo methods as a function of temperature. The bond distribution function for a low temperature Monte Carlo run (24 °K) and a high temperature run (400 °K) is plotted as a function of temperature. (AIP)
Isoelectronic energy changes from energy–density functionals
Authors: Sen K. D.
Published: February 2003

A comparison is made of the ratio of the total energy of neutral atom to that of the monopositive ion as calculated by the energy formula given by Parr et al1 and by Politzer and Levy.4 The corresponding Hartree-Fock values are also given. (AIP)
Photodynamics of polyenes: The effect of electron correlation on potential surfaces
Authors: Lasaga A. C. , Aerni R. J. , Karplus M.
Published: February 2003

Ground and excited state potential surfaces for polyenes are calculated by a method that uses an empirical force for sigma electrons and a modified Pariser–Parr–Pople model with configuration interaction through double excitations for the π-electrons. The effects of electron correlation on the energies, equilibrium geometries, and vibrational frequencies for the ground state and the two lowest excited states (2 1Ag−, 1 1Bu+) of butadiene, hexatriene, and octatetraene are studied and compared with the available experimental data. An analysis of the normal modes of vibration provides an understanding of some of the trends as a func- tion of chain length. The model is used also to examine the ground-state tortional potential in which electron correlation plays an important role.
Effect of static correlations on the pair friction coefficient
Authors: Cukier Robert I. , Kapral Raymond , Mehaffey J. R.
Published: February 2003

A calculation of the spatial dependence of the pair friction tensors ζij(r12), (i, j=1,2) for two hard sphere solute particles in a hard sphere fluid is presented. The calculation is based on a kinetic theory expression for the pair friction tensor. The contribution from dynamically uncorrelated collisions is computed here. (We do not consider the contribution from correlated collisions, which are important at high density.) The friction tensor is found to have a significant dependence on the solute pair separation, which arises from static correlations among the bath and solute particles.
Extension of Flory’s statistical theory at elevated pressures
Authors: Mishra R. L.
Published: February 2003

Flory’s statistical theory has been used to calculate ultrasonic velocity and surface tension over broad ranges of temperature and pressure in liquid argon, krypton, xenon, nitrogen, and water. The results have been compared with experimental measurements and it has been found that the agreement between the two is excellent.
Lattice dynamics of solid N2 with an a
b i
n
i
t
i
o intermolecular potential
Authors: Luty T. , van der Avoird A. , Berns R. M.
Published: February 2003

We have performed harmonic and self-consistent phonon lattice dynamics calculations for α and γ N2 crystals using an intermolecular potential from ab initio calculations. This potential contains electrostatic (multipole) interactions, up to all R−9 terms inclusive, anisotropic dispersion interactions up to all R−10 terms inclusive, and anisotropic overlap interactions caused by charge penetration and exchange between the molecules. The lattice constants, cohesion energy, the frequencies of the translational phonon modes and the Grüneisen parameters for the librational modes are in good agreement with experimental values, confirming the quality of the potential. The frequencies of the librational modes and those of the mixed modes are less well reproduced, especially at temperatures near the α–β phase transition. Probably, the self-consistent phonon method used does not fully account for the anharmonicity in the librations.
Magnetic relaxation under fast internal rotation in liquids
Authors: Versmold H.
Published: February 2003

In previous work magnetic relaxation under internal rotation frequently has been discussed in terms of the rotational diffusion model even for systems with rather low internal barriers. Here the internal rotation is taken as an ’’extended diffusion’’ process. In the limit of fast internal rotation, a modification of the relaxation equations commonly used occurs. The influence of the modifications on the final results for orientational correlation times is discussed.
The surface tension of lipid water interfaces: Monte Carlo simulations
Authors: Scott H. L. , Lee C. Y.
Published: February 2003

We present the results of several computer simulations using a model for the head group water interface of a lipid bilayer. Simulations were performed using the Monte Carlo method, enhanced by a ’’half-umbrella sampling’’ algorithm we developed in an earlier paper. Our results can be used in a comparative way, along with the earlier results for pure water, to estimate the effective dipole moment of a typical phospholipid in a bilayer in excess water.
Dynamics of molecular scattering from stepped surfaces
Authors: Yinnon A. T. , Minglegrin U. , Gerber R. B.
Published: February 2003

The patterns of angular intensity distribution in molecular scattering from ordered stepped surfaces are studied by the classical trajectory method. Using the stepped Cu(117) surface as a representative model, the following results are obtained: (i) There is a nonspecular intensity structure due to the steps corrugation. In the angular range where data exists, intensities and peak positions are in good accord with recent experiments. (ii) A structure that is a secondary rainbow pattern is found superimposed on the familiar surface rainbow. The effect is due to multiple scattering related to step geometry. It is predicted that the secondary rainbow effect will be very typical in high incidence-angle scattering from ordered stepped surfaces. (iii) A new surface-scattering resonance is predicted that is a consequence of the ordered steps structure. It is expected that these resonances (long-lived trajectories) can be the basis of a significant surface-trapping mechanism. Capture into such resonances (step-gliding resonances) is possible even at incidence energies that are very high compared with the well depth of the atom–surface potential. Finally, a method is given by which the step height and step size may be readily estimated from measured angular intensity distributions. Application of this estimate to simulated data from calculations give satisfactory results for the step parameters.
Determination of proton affinities from the kinetics of proton transfer reactions. VII. The proton affinities of O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO
Authors: Bohme D. K. , Mackay G. I. , Schiff H. I.
Published: February 2003

The flowing afterglow and selected ion flow tube techniques are applied in a room temperature study of the kinetics of proton-transfer reactions of the type XH++Y?YH++X for X or Y=He, H2, O2, Kr, O, N2, Xe, CO2, CH4, CD4, N2O, OH, and CO, and for the deuteration of O2 by D3+. Equilibrium constants are determined and changes in thermodynamic state properties (ΔG°, ΔH°, ΔS°) are derived for the reactions with X/Y=H2/O2, O2/Kr, H2/Kr, H2/N2, O/N2, N2/Xe, Xe/CO2, CO2/CH4, CH4/N2O, and N2O/CO. Proton affinities are reported for O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO, together with the heats of formation of their protonated species. Also a correlation is presented between the kinetic and thermodynamic results obtained in this study.
Radiationless transitions in molecular ions: Monochloroacetylene and dichloroacetylene cations
Authors: Dujardin Gérald , Leach Sydney , Taieb Guy , Maier John P. , Gelbart William M.
Published: February 2003

We apply recent theories of radiationless transitions to the case of photon emission from molecular ions. Mono- and dichloroacetylene cations are formed in excited electronic states by 21.22 eV (He i) or 16.85 eV (Ne i) photon excitation of the parent molecules. Multiexponential decay is observed for emission from the ? 2Π(g) state of each ion as previously reported for 30 V electron impact excitation. Emission quantum yields are determined in the photon excitation experiments. Coupling between the ? 2Π(g) state and high vibrational levels of the ? 2Π(u) ground state is invoked to explain the data presented. The ’’strong-coupling’’ theory of ’’intermediate’’ case radiationless transitions is used to infer values for average coupling energies, densities of states, and level widths. We conclude by treating several possible explanations for the fate of ’’hot’’ ground-electronic-state ions: (i) intramolecular vibrational relaxation; (ii) collisional quenching; and (iii) infrared emission.
Collinear triatomic reactions described by polar Delves coordinates
Authors: Hauke G. , Manz J. , Römelt J.
Published: February 2003

Delves, i.e., polar coordinates with the three-atom coincidence as origin, are adapted for computations of collinear collisions, involving vibrationally inelastic, reactive, and dissociative channels and for arbitrary masses. The exact quantum reaction probabilities are obtained by S matrix propagation from the strong interaction region towards the asymptotic reactant, product and dissociation configurations. The new method is approved by excellent agreement with the exact solution of an idealized model reaction with L-shaped potential and infinite walls.
Ion–molecule reactions of He+, Ne+, N+, N2+, N3+, and N4+ ions with Hg atoms and HgBr2 molecules at thermal energy
Authors: Johnsen Rainer , Biondi Manfred A.
Published: February 2003

A drift tube–mass spectrometer apparatus has been used to investigate a number of reactions of rare-gas and nitrogen ions with mercury (II) bromide and with elemental mercury (of interest for laser modeling). Rate coefficients with HgBr2 reactant are found to be large (on the order of 3–7×10−10 cm3/sec) at 300 K with ordinary or dissociative charge transfer the dominant reaction mechanism. Except for the reaction N3++Hg, reactions of nitrogen ions with mercury atoms are found to be moderately or very slow.
Diffusion-controlled kinetics of protein domain coalescence: Effects of orientation, interdomain forces and hydration
Authors: Zientara Gary P. , Nagy Janice A. , Freed Jack H.
Published: February 2003

The numerical methods of Zientara and Freed [J. Phys. Chem. 83, 3333 (1979)] have been used to study the diffusion-controlled kinetics of domain coalescence in order to ultimately consider the time evolution of protein folding. The mean coalescence lifetime for a domain pair has been calculated using the eigenfunction expansion method and finite differences in the solution of a modified form of the Smoluchowski equation. This approach allows for an orientational preference in the domain coalescence process, which has been studied throughout the complete range of reactivities. Three cases of interdomain forces were investigated, one of which represents the shielding of charged domains by ions in solution. As the forces vary from the strongly repulsive to the strongly attractive in these cases, the coalescence lifetime decreases by several orders of magnitude. In addition, a hydration shell model, which provides an activation barrier to coalescence, has been analyzed. The lifetimes resulting from this model were observed to depend strongly on the location and extent of the hydration shell. Anisotropic initial conditions were also incorporated causing, in some cases, non-negligible effects upon the coalescence lifetimes.
CS and IOS approximations for fine structure transitions in Na(2P)–He(1S) collisions
Authors: Fitz D. E. , Kouri D. J.
Published: February 2003

The l-average CS and IOS approximations are extended to treat fine structure transitions in 2P atom–1S atom scattering. Calculations of degeneracy averaged probabilities and differential cross sections for Na(2P)+He(1S) collisions in the CS and IOS methods agree well with the CC results. The present nonunitarized form of the CS approximation fails to properly predict all of the jm→j′m′ sections and in particular leads to a selection rule forbidding jm→j–m transitions for j=half-odd integer values.
Crossed molecular beam studies of chemiluminescent reactions: F2+I2, Br2, and ICl
Authors: Kahler C. C. , Lee Y. T.
Published: February 2003

The chemiluminescent bimolecular halogen–halogen reactions, F2+I2, Br2, and ICl, have been studied by the crossed molecular beam technique. Undispersed chemiluminescence was measured as a function of collision energy and, for I2+F2, as a function of the two beam pressures. Although no spectra were obtained to positively identify the emitters as IF*, ClF*, and BrF*, arguments are given to support this identification. The observed reaction thresholds of 4.2 and 5.9 kcal/mole for I2+F2 and ICl+F2, respectively, are the same as the threshold energies for production of the stable trihalogens I2F and ClIF. This coincidence of threshold energies, as well as similar high collision energy behavior, implies that the chemiluminescent reaction proceeds via a stable trihalogen intermediate. This mechanism can explain our results and the results of other workers without resorting to a symmetry forbidden four center reaction mechanism. A threshold of 11.3 kcal/mole was found for Br2+F2; no threshold for Br2F has been previously reported. Laser enhancement of the I2+F2 reaction was attemped, but no enhancement was seen.