bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum topology of molecular charge distributions. III. The mechanics of an atom in a molecule
Authors: Bader R. F. W.
Published: February 2003

The variation of the atomic action integral yields Schrödinger’s equations-of-motion and an atomic statement of the variational principle. The atom and its average properties are defined by the variational principle together with the requirement that they satisfy the Heisenberg equation-of-motion. Schrödinger’s equations define the components of the energy-momentum tensor. The divergence equations satisfied by the spatial components of this tensor, the stress tensor, yield an expression for the resultant force exerted on a single electron at a given point in space and at a given time by the average motion of the other particles in the system. The integration of this force density over the space of an atom yields an equation-of-motion for an atom in a molecule identical to that determined by the generalized variational principle. Thus the action principle yields a local description of the mechanical properties of an atom and a definition of their average values. The force density is expressible in terms of a stress tensor which is a functional of the first-order density matrix. The virial of this force yields the potential energy density of a single electron moving in the average field generated by the motion of the other particles in the system. This enables one to define the total energy density as a functional of the first-order density matrix. The atomic average of this energy density is identical to the average energy of an atom in a molecule as defined through the atomic statement of the variational principle. The energy density defined in this manner has the essential property of predicting that if the distribution of charge for an atom is identical in two different systems or at different sites within a given system (e.g., a solid) then the atom will contribute identical amounts to the total energy in both instances. Matter is manifest in real space through its distribution of charge. Those properties of matter which are extensive are so as a consequence of the periodicity of the charge distribution at the atomic level. The equivalence of the quantum mechanical definition of an atom with that determined by the topological properties of the charge distribution is demonstrated. It is shown that the special properties possessed by the atomic action integral are a direct consequence of the topological definition of an atom as the union of an attractor and its basin. The relationship between the topological and mechanical properties of the charge density is pursued through a study of the topological properties of the first-order density matrix. As demonstrated, the properties of the first-order matrix determine both the topology and the mechanics of the charge density.
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o model calculations of graphite: Prismatic surface electronic density
Authors: Butkus Aldona M. , Fink William H.
Published: February 2003

A b initio calculations which permit the approximation of a semi-infinite lattice by a finite cluster are reported for the (112̄0), (101̄0), and (303̄0) prismatic surfaces of graphite. Reference SCF calculations are carried out for all of the clusters treated. Mulliken populations are calculated using both the SCF and the model wave functions. Clusters of eight carbons or less are considered which include atoms up to the third layer below the surface with bulklike charge distributions achieved at the second bulk layer. The calculations show weak interaction between atoms in adjacent stacking planes of the graphite lattice. On the (101̄0) and (303̄0) surfaces along the C0 direction neutral atoms alternate with positively charged carbons. Only a slightly positive charge is calculated for carbons on the (112̄0) surface.
‘‘Defect state model’’ and effect of transition metal impurities on metal-free phthalocyanine: Electrical and photoconductive properties
Authors: Cheng Y. C. , Loutfy R. O.
Published: February 2003

A mechanistic study of the effect of transition metal impurities on trap density, electrical and photoelectrical properties of metal-free phthalocyanine was carried out. The experimental results showed that electrical and photoconductive properties of H2Pc were a function of trap density (nt) and concentration of metallic impurities (particularly iron). The results were analyzed in terms of several theoretical models. Both the hydrogenic-type shallow impurity state model and conduction due to bridging of host molecules via iron impurity atoms were incompatible with the results. An excellent description of the observed electrical and photoconductive behavior of H2Pc as a function of trap density and impurity can be given using a defect state model, analogous to deep state in inorganic system. This model correctly predicts the dependence of specific conductivity, σ, of H2Pc on the inverse of trap density (1/nt) at low concentration and on 1/nt2 at high trap concentration. Similarly, the model offers an explanation of the change in the dependence of conductivity under illumination from 1/Ne to 1/Ne1/2 as a function of increased trap density.
Magnetic multipoles in nonresonance time dependent fields
Authors: Sanctuary B. C. , Garisto Frank
Published: February 2003

The time dependence of the density operator for an arbitrary number of uncoupled spins in a resonant field has recently been presented [B. C. Sanctuary, J. Chem. Phys. 73, 1048 (1980). In this paper, the solutions are extended to the nonresonant case and are given in terms of rotation matrices.
23Na second-order quadrupolar shifts and heat capacity anomalies in Na β-alumina
Authors: Bjorkstam John L. , Ferloni Paolo , Villa Marco
Published: February 2003

In the temperature region 100–140 K the second-order quadrupolar shifts of 23Na in β-alumina undergo a gradual but unusual change. In the same temperature range, contributions to the heat capacity of atoms in the conducting plane exhibit a maximum. These facts are considered as evidence for a 2D ’’melting transition’’ in the conducting plane of β-alumina. The nature of the phenomena responsible for these anomalies is discussed.
A modified moment method and irreversible thermodynamics
Authors: Eu Byung Chan
Published: February 2003

We investigate a method of solving the Boltzmann equation especially with a view to a deeper understanding of irreversible thermodynamics for systems in nonequilibrium state. By modifying the conventional moment method for the Boltzmann equation, we show that there can result irreversible thermodynamics with attendant evolution equations for macroscopic variables consistent with the second law of thermodynamics. An important result is the extended Gibbs relation, TdS=dE+pdv- ∑ iμ̂idci+ ∑ l ∑ iX̂i(l)⊙dΦi(l)whereT is the temperature, S the entropy density, E the internal energy density, v the specific volume, μ̂i the chemical potential, ci the concentration, X̂i(l) the generalized thermodynamic force conjugate to Φi(l) which can be stress tensor, heat flux, material flux, and possibly other higher moments. This relation is valid for any nonequilibrium state and can be used for studying the geometric structure of entropy in the extended Gibbs space {E,v,ci,Φi(l)}. It is shown that linear irreversible processes correspond to the stationary processes for which (dΦi(l)/dt)=0 among other conditions. The usual equilibrium Gibbs relation is recovered from the extended Gibbs relation in such a case. The evolution equations obtained in this paper can serve as a guide and a model for future phenomenological formulation of irreversible thermodynamics for systems removed far from equilibrium or for nonlinear processes.
R-variation of electronic transition moments from vibrationally crowded spectra: the B–X and D–X transitions of xenon fluoride
Authors: Smith Allan L. , Messing Itzhak , Gelernt Barry
Published: February 2003

Using photographic flash spectroscopy of Xe/F2 mixtures, we have studied the B(1/2)–X(2Σ+) and D(1/2)−X(2Σ+) transition of XeF in absorption between 241 and 358 nm. The spectra exhibit extensive sequence crowding due to overlapping hot bands. To determine the R-variation of the B–X and D–X electronic transition moments we use band cluster analysis, in which the R centroids of bands contributing to a given cluster are shown to be similar; i.e., the R centroid is a smoothly varying function of bandhead wavelength. Absolute transition moments are derived by normalizing our relative absorption measurements to the measured radiative lifetime of the v′=0 level of the B(1/2) state. The B–X moment is 2.70±0.22 D, independent of R between 2.30 and 2.54 Å. The D–X moment varies linearly from 2.255 D at 2.25 Å to 2.413 D at 2.50 Å (±20%). The computed radiative lifetime of the v′=0 level of the D(1/2) state is 10.0±2.0 nsec.
Laser predissociation spectroscopy of the f 4Πg state of O2+
Authors: Helm H. , Cosby P. C. , Huestis D. L.
Published: February 2003

Two quasibound vibrational levels of the f 4Πg state have been observed by monitoring O+ photofragments resulting from absorption of laser radiation by the a 4Πu state. The first spectroscopic constants for the f state have been derived from rotational and isotopic analyses. Measurements of the predissociation linewidths and photofragment kinetic energies have been used to refine estimates of the barrier in the f state potential curve and to identify likely predissociation mechanisms.
Infrared and visible absorption spectra and photochemistry of the Ch2FX+, CHFX+, F–H⋅⋅⋅(CHX)−, and X–H⋅⋅⋅(CHF)− molecular ions in solid argon
Authors: Prochaska Frank T. , Andrews Lester
Published: February 2003

Samples of CH2FX (where X=Cl, Br, I), 13CH2FCl, and CD2FCl at high dilution in argon were deposited at 15 K and simultaneously photoionized by argon resonance radiation from a microwave discharge, and the products studied by infrared and visible-ultraviolet spectroscopy. A large number of new absorptions were observed which have been grouped by photolysis, diffusion, and isotopic data. The parent cations CH2FX+ show increased C–X stretching frequencies and decreased C–H stretching frequencies relative to the neutral molecule. The daughter cations CHFX+ show increased C–F stretching and H–C–F hydrogen deformation frequencies, indicative of the enhanced pi bonding in the planar cation compared to the neutral radical. The C–F and C–X stretching vibrations of the neutral CFX carbenes are also identified. Strong, broad absorptions showing small carbon-13 and large deuterium shifts are assigned to the F–H stretching and hydrogen deformation modes of the intramolecular hydrogen-bonded parent anion F–H⋅⋅⋅(CHX)−, while other absorptions showing the proper isotopic shifts are assigned to the X–H and C–F stretching vibrations of the hydrogen-bonded species X–H⋅⋅⋅(CHF)−.
Double resonance and high resolution infrared spectroscopy of the CF4 ν3 fundamental. I. Infrared-radiofrequency double resonance
Authors: Takami Michio
Published: February 2003

Pure rotational spectrum of CF4 in the v3=1 state was investigated by infrared–radiofrequency double resonance. A semiconductor tunable diode laser was used as an infrared pumping radiation source. 176 transitions among tetrahedral fine structure components of the R=J−1, J and J+1 Coriolis sublevels were measured with 100 kHz resolution. The transitions in the R=J−1 state showed large frequency anomalies caused by a perturbation from the 2ν4 state. The following constants were determined from the transitions in the R=J+1 and J states: α224=−750.0(3), F134 =12.47 (6), D044=0.144 (4), G244=−0.120 (2), G246=0.0772 (9), H044=−0.043 (3)×10−3 and H066=0.0339 (14)×10−3 in kHz, where the figures in parentheses are standard deviations in units of the last digit.
Thermal rate coefficients for reactions involving 2P1/2 and 2P3/2 argon ions and several neutral molecules
Authors: Rakshit A. B. , Warneck P.
Published: February 2003

Reactions of argon ions with CO, N2, O2, NO, N2O, CO2, and H2 were investigated at different total pressures with a selected ion-drift chamber mass spectrometer. The rate data obtained indicate the presence of excited argon ions in addition to argon ions in the ground state. The excited ionic species has been assigned to the 2P1/2 metastable state, and these ions were found to undergo collisional quenching as well as reaction. With CO, N2, and O2 the Ar+(2P1/2) ions react faster than the Ar+(2P3/2) ground state ions and quenching is less significant, while with N2O, CO2, and H2 the Ar+(2P1/2) ions are predominantly quenched. The rate coefficients for the ground state argon ions are in reasonable agreement with recent data obtained by flow techniques. NO provides an exception, the reasons for this observation are discussed.
Quantum mechanical study of elastic scattering and rotational excitation of CO by electrons
Authors: Onda Kunizo , Truhlar Donald G.
Published: February 2003

We report close coupling calculations of differential, integral, and momentum transfer cross sections for pure elastic scattering and rotational excitation of CO by electron impact. The calculations are based on a static charge distribution that has correct dipole and quadrupole moments, has cusps at the nuclei, and is augmented by an SCF treatment of charge polarization and a local approximation for exchange. The rotationally summed cross sections, with no adjustable parameters in the scattering calculation, are in reasonably good agreement with the experimental cross sections but are somewhat larger at small scattering angles. The state-to-state differential cross sections show several interesting features, including very large contributions to small-angle scattering from large angular momenta and a ’’propensity rule’’ favoring even Δj over odd Δj at almost all scattering angles for Δj≲4 where Δj is the change in rotational quantum number.
The stable states picture of chemical reactions. I. Formulation for rate constants and initial condition effects
Authors: Northrup Scott H. , Hynes James T.
Published: February 2003

The stable states picture (SSP) of chemical reactions is used to derive flux time correlation function (tcf) formulas for reaction rate constants. These formulas, which apply to both gas phase and condensed phase reactions, are interpreted in terms of the flux out of an internally equilibrated stable reactant and the ensuing irreversible flux into a stable product. The determination of the rate constants by dynamics in an intermediate region lying between these stable states is illustrated for a simple model of barrier crossing in liquids. Generalized rate constant expressions which hold when internal nonequilibrium in the stable states is important are derived and discussed. The SSP approach is also used to derive tcf expressions for short time initial condition effects which carry information on reactive dynamics beyond that contained in rate constants. As an illustration, it is shown how the SSP formulation provides a starting point for the resolution of primary and secondary recombination in liquid state photodissociation reactions.
The stable states picture of chemical reactions. II. Rate constants for condensed and gas phase reaction models
Authors: Grote Richard F. , Hynes James T.
Published: February 2003

The time correlation function (tcf) formulas for rate constants κ derived via the stable states picture (SSP) of chemical reactions are applied to a wide variety (a–d) of gas and solution phase reaction models. (a) For gas phase bimolecular reactions, we show that the flux tcf governing κ corresponds to standard numerical trajectory calculation methods. Alternate formulas for κ are derived which focus on saddle point surfaces, thus increasing computational efficiency. Advantages of the SSP formulas for κ are discussed. (b) For gas phase unimolecular reactions, simple results for κ are found in both the strong and weak coupling collision limits; the often ignored role of product stabilization is exposed for reversible isomerizations. The SSP results correct some standard weak coupling rate constant results by as much as 50%. (c) For barrier crossing reactions in solution, we evaluate κ for a generalized (non-Markovian) Langevin description of the dynamics. For several realistic models of time dependent friction, κ differs dramatically from the popular Kramers constant friction predictions; this has important implications for the validity of transition state theory. (d) For solution reactions heavily influenced by spatial diffusion, we show that the SSP isolates short range reaction dynamics of interest and includes important barrier region effects in structural isomerizations often missed in standard descriptions.
The CdHg (a) state: Fluorescence kinetics and absorption
Authors: McGeoch M. W.
Published: February 2003

The molecular fluorescence of CdHg has been studied following excitation of Hg2 at 266 nm. The fluorescence is modeled by giving the CdHg (a) state a lifetime of 2.4 μsec and including a reservoir of metastable Cd2Hg molecules. The transmission of this system has been monitored at wavelengths between 390 and 514 nm as a function of cadmium density and temperature yielding results consistent with the Cd2Hg hypothesis. Excited state absorption has been measured for CdHg (a), Cd2Hg, pure Hg, and pure Cd. The absorption intrinsic to CdHg (a) has a peak cross section of 5×10−19 cm2 at 450 nm and a width of 90 nm at half-maximum.
Deuteron spin–lattice relaxation from hindered rotations in molecular crystals
Authors: Pratt J. C. , Watton A. , Petch H. E.
Published: February 2003

The 2D nuclear spin–lattice relaxation is calculated for the situation in which molecular groups containing n deuterons undergo thermally activated hindered reorientations enabling each of the spins to sample each of n available sites, all of which are assumed to have quadrupole couplings (e2qQ/h) of equal magnitude. The rotations of the molecular group are treated classically, as simultaneous, independent Poisson processes. Use of the theory is illustrated by reference to various possible models for the motion of −CD3 and ND+4 groups in molecular crystals.
The spectral opacity of triatomic carbon measured in a graphite tube furnace over the 280 to 600 nm wavelength range
Authors: Snow Walter L. , Wells William L.
Published: February 2003

The opacity of linear triatomic carbon (C3) was measured in a graphite tube furnace from 280 to 600 nm to supplement the earlier measurement of Brewer and Engelke. Data are presented for a maximum centerline temperature range of 2720–3060 K.
Microwave optical double resonance of NH2. VI. Ground state of NHD
Authors: Steimle T. C. , Brown J. M. , Curl R. F.
Published: February 2003

Microwave optical double resonance studies of the ground vibronic state of NHD have been carried out. Both a-type rotational transitions between K doublet levels and magnetic dipole transitions between fine structure components have been observed. Analysis of the hyperfine structure completes the determination of the hyperfine coupling tensor for the proton. It is found that one of the principal axes of the tensor nearly coincides with the NH bond direction and that this magnetic dipole coupling tensor is reasonably consistent with the odd electron being in a p orbital on the N atom perpendicular to the molecular plane. The MODR observations have been combined with ground state combination differences from previous optical studies to give improved rotational and fine structure constants. It also has been possible to determine the magnitude of the off-diagonal component of the spin–rotation tensor, εab, as 1.07±0.09 GHz, from the mixing of states differing by 1 in Ka.
Microwave optical double resonance of HNO: Rotational spectrum in Ã1A′′(100).
Authors: Takagi Kojiro , Saito Shuji , Kakimoto Masao , Hirota Eizi
Published: February 2003

Rotational transitions in the ?1A″(100) state of HNO were observed using the technique of microwave optical double resonance. The HNO molecule was produced in a fast flow system by the reaction of discharged oxygen with a mixture of propylene and NO. Eighteen rotational lines observed in the frequency regions of 8 to 157 GHz and rf were analyzed to give rotational constants and centrifugal distortion constants. Perturbations were found in the K-type doubling frequencies of K−1 =1 and 2.
Reaction path Hamiltonian: Tunneling effects in the unimolecular isomerization HNC→HCN
Authors: Gray S. K. , Miller W. H. , Yamaguchi Y. , Schaefer H. F.
Published: February 2003

The reaction path Hamiltonian model recently formulated by Miller, Handy, and Adams [J. Chem. Phys. 72, 99 (1980)] is applied to the unimolecular isomerization HNC→HCN. The reaction path, and the energy and force constant matrix along it, are calculated at the SCF level with a large basis set (’’double zeta plus polarization’’), and the microcanonical rate constant k(E) is computed in the energy range near and below the classical threshold of the reaction. It is seen, for example, that rates as fast as 105 sec−1 can occur at energies ∼8 kcal/mole below the classical threshold.
A unified theory of dissociation
Authors: Doll J. D.
Published: February 2003

We present here a unified theory of molecular dissociation. The theory is a generalization of Slater’s unimolecular work. Assumptions concerning normal mode behavior are removed and a common formalism suffices for various statistical ensembles. The quantum-mechanical extensions of the theory are immediate.
Eyring activation parameters for the relaxation processes of some asymmetric diaryl molecules in a polystyrene matrix
Authors: Desando M. A. , Walker S.
Published: February 2003

Measurements of the dielectric absorption of a series of asymmetric diaryl ketones and ethers of the type X–C6H4–Y–C6H5 (Y=0, CO, and X=OH, F, Cl, Br, NO2, and C6H5) and 2-benzoylpyridine have been made in polystyrene in the frequency range 102–105 Hz over a wide temperature range (77–330 K). The Eyring activation parameters have been determined, and these indicated the occurrence of a molecular relaxation process in all cases, except 4-biphenyl phenyl ether, where only phenoxy group rotation has been detected. An intramolecular energy barrier has also been determined which is slightly greater than that for the rotation of a methoxy group in aromatic methoxy compounds. The enthalpies of activation have been estimated for molecular relaxation. Correlations have been obtained for the molecular relaxation processes, between ΔGE and ΔHE and the volume swept out on reorientation. The factors governing the relative magnitude of the molecular activation energy parameters have been considered.
A molecular beam investigation of the oxidation of CO on Pt[9(111)×(100)]
Authors: Fair J. A. , Madix R. J.
Published: February 2003

The CO oxidation on Pt[9(111)×(100)] was studied by molecular beam relaxation spectroscopy (MBRS). The reaction proceeded via the reaction of adsorbed CO and adsorbed oxygen. No evidence for direct reactive collisions between gaseous CO and adsorbed atomic oxygen was seen. The second order rate constant was measured by linearizing the reaction system to be 10−7 exp{−RT9700 kcal/mole} cm−2 s−1. The relatively low pre-exponential factor was explained by transition state theory on the basis of a high partition function for adsorbed carbon monoxide obtained previously from studies of CO desorption on this surface.
A test of the adiabaticity and kinetic energy shift factors in the energy corrected sudden scaling theory
Authors: DePristo Andrew E.
Published: February 2003

Cross sections are calculated for rotation-rotation processes in the H2-H2 system.(AIP)
C–H hyperconjugation in alkyl benzene cations as revealed by position-dependent isotope effects on nonradiative decay rates of electron donor–acceptor complexes
Authors: Okajima S. , Lim Bee T. , Lim E. C.
Published: February 2003

A major methyl deuteration effect on the nonradiative decay rate of electron donor-acceptor complexes in reported. This effect indicates strongly the importance of c−h hyperconjugation in alkyl lethzene cations.(AIP)
Comment on the depolarized Rayleigh intensity anomaly in the critical mixture of nitroethane and isooctane
Authors: Dote J. L. , Kivelson D. , Knobler C. M.
Published: February 2003

The data of Zalczer and Beysens1 regarding the intensity measurements of depolarized Rayleigh scattering line in a critical mixture of nitroethane and isoctane is analyzed. Similar data of Ref. 2 for pure nitrobenzene is also reexamined. It is concluded that the intensity behavior in the mixture is not associated with a critical anomaly. (AIP)
Electrostatic potential–electronic density relationships in atoms. II
Authors: Politzer Peter
Published: February 2003

An exact equation has been derived that relates the derivative of the electrostatic potential at any radial distance from the nucleus of a neutral atom to the amount of electronic charge that is located beyond that radial distance. This equation assumes a particularly simple form at distances corresponding to minima in the radial density function, and can be used to show that at such a distance, rm, the electrostatic potential due to the electronic charge beyond rm is exactly half (but with opposite sign) of that produced by the nucleus and the electronic charge within the radial distance rm. When applied at the outermost radial density minimum, which has been proposed as the boundary between the core and valence regions of a ground-state neutral atom, the new equation can be used to significantly improve a previously derived atomic energy formula.
Applicability of self-consistent field techniques based on the complex coordinate method to metastable electronic states
Authors: McCurdy C. William , Rescigno Thomas N. , Davidson Ernest R. , Lauderdale Jack G.
Published: February 2003

Hartree–Fock theory is applied to resonance states of an atomic Hamiltonian under the complex coordinate transformation. It is concluded that for shape resonances restricted Hartree–Fock theory provides a useful and practical approach to the problem of computing the complex resonance energy. Numerical results are presented for the low-energy 2P shape resonance in e–Be scattering. With properly chosen basis functions the resonance energy obtained in these calculations is practically independent of the phase of the complex scaling parameter for a wide range of values. Application of this technique to molecular resonances is discussed. The widths of Feshbach resonances cannot be obtained from the theory in its present form, but it is suggested that a complex coordinate form of multiconfiguration self-consistent field theory may be appropriate for that case.
An MCSCF characterization of the HeH2+ 2 2A1(2Σ+) polarization state. A radiative mechanism for the production of H2+ from thermal He++H2 collisions
Authors: Hopper Darrel G.
Published: February 2003

A quantitative multiconfiguration self-consistent field treatment of the potential curves for the C2v and C∞v approach of an He+(1 2S) ion to H2(X 1Σg+) has been made. Second-root same-symmetry orbital optimization techniques were employed in order to treat the 2 2A1(2 2A′,2 2Σ+) state involved. These computations have established that the shallow He+–H2 ion–molecule polarization well is characterized by a C2v minimum with the attributes (Eb, ReHe–H2, ReH2) =(0.091 eV, 2.345 Å, 0.714 Å). The fundamental vibrational frequency for the pseudodiatomic He+–H2 is 284 cm−1. As RHe–H2 decreases further the difference between the C∞v and C2v cut narrows as the system approaches the high interaction region. The availability of this polarization state suggests a collisional–radiative mechanism for the production of H2+ from the reaction of He+(1 2S) with H2(X 1Σg+) at thermal energies, with or without a third body M He+(1 2S)+H2(X 1Σg+) M→ He+–H2(2 2A1) He+–H2(2 2A1)→[He–H2+(1 2A1)]°+hν(153 nm) [He–H+2(1 2A1)]°→He(1 1S)+H+2 (X 2Σg+,v)+KE. The polarization state also provides a thermal pathway for vibrational deactivation of hydrogen by helium ions. These thermal mechanisms are discussed in relation to the well-known tunneling mechanism yielding H+ and with regard to planetary and interstellar chemistry.
The numerical evaluations of the density of states weighted Franck–Condon factor in large molecules. Effects of frequency changes
Authors: Mikami Yasushi
Published: February 2003

The numerical integration method (NIM) is applied to calculations of the density of states weighted Franck–Condon (DWFC) factor which plays an important role in the theory of nonradiative transitions. The 200 point Legendre–Gauss quadrature formula is used to save computing time. Values of the integrand are given with the quadruple precision to avoid accumulated errors occuring in the numerical integration. The illustrative calculations are carried out for the T1→S0 intersystem crossing in benzene. If frequency changes of all vibrational modes are taken into account, the energy gap law applies very well, but it fails without frequency changes. This fact suggests that the ordinary saddle point method based on the harmonic displaced potential surface model is inaccurate. The DWFC factor is sensitive to frequency changes of a high frequency mode which plays an important role in nonradiative transition. When low and medium frequency modes are added, as a group, to high frequency ones, they give a significant effect upon the DWFC factor. If a frequency change of a low frequency mode is hypothetically reduced to an extremely low value, the DWFC factor rapidly increases. This relates to the proximity effect by Wassam and Lim in the nonradiative transition in N-heterocyclic aromatic hydrocarbons. Finally, Metz’s method is discussed.
Graph theoretical characterization of NMR groups, nonrigid nuclear spin species and the construction of symmetry adapted NMR spin functions
Authors: Balasubramanian K.
Published: February 2003

NMR group defined by Woodman is shown to be the generalized wreath product group of the NMR graph which is constructed with protons as vertices and edges representing nuclear couplings. The NMR graph can be expressed as a generalized composition of its quotient graph and various types. It is shown that the NMR group is the automorphism group of the NMR graph that preserves the coupling matrix defined here. Using the representation theory of generalized wreath product groups developed in an earlier paper of the present author, the character tables of NMR groups can be obtained. The character tables of certain NMR groups are presented. The quotient graph of the NMR graph is shown to be the composite particle graph. The automorphism group of the quotient NMR graph is the symmetry group of the composite particles, preserving the NMR coupling constants. An iterative algorithm is formulated for obtaining the automorphism group of the composite particle tree. A combinatorial approach is expounded for identifying the nuclear spin species of nonrigid and rigid molecules. The coalescence diagrams describing the effect of nonrigidity on nuclear spin species are introduced and obtained to exemplify the utility of the proposed method. It is shown that using the automorphism group of the quotient graph, the symmetry adapted composite particle spin functions can be constructed. We illustrate this method with 2,3-dimethylbutane. The nuclear spin Hamiltonian matrix of 2,3-dimethylbutane of order 214×214 is reduced to a matrix of order 64×64 by the composite particle method. This matrix can be blocked in the symmetry adapted basis set constructed through the automorphism group of the quotient graph into 40 matrices of order 1×1 and 12 matrices of order 2×2.
Detailed comparison of the Williams–Watts and Cole–Davidson functions
Authors: Lindsey C. P. , Patterson G. D.
Published: February 2003

The distribution function of relaxation times underlying the nonexponential relaxation function of Williams and Watts is derived and compared with the analogous Cole–Davidson distribution function. In order to make the comparison between the two distribution functions, a simple empirical relationship between the Cole–Davidson and Williams–Watts parameters was determined which may be used to compare data analyzed using the two fitting functions. Although the relaxation functions are similar to each other, the distribution functions are quite dissimilar. The Cole–Davidson distribution shows a sharp long time cutoff, while the Williams–Watts distribution decays approximately exponentially at long times. Finally, several useful relations between relaxation and distribution functions are summarized or derived, and the limitations of deriving distribution functions from relaxation functions are discussed.
Orientational phases of methane bilayers
Authors: Maki Kazuo , O’Shea Seamus F.
Published: February 2003

Orientational phases of methane bilayers have been studied using a combination of molecular field calculations and Monte Carlo simulations. In the free standing bilayer, whose dynamics are determined entirely by internal octopole–octopole interactions, the MF method predicts that the high temperature disordered phase can branch into a partially ordered intermediate phase with either ferro or antiferrorotational combinations of the orientations of the molecules in the individual layers. Each of these structures is transformed into a low temperature structure by a second phase transition, in the ferro case to a stable structure, and in the antiferro case to a metastable one. The simulations find only the ferro branch. A close relationship is found between these phases and those of the three dimensional octopolar solid. The consistency of the two methods and their relative strengths and weaknesses are discussed. We have also studied the tripod bilayer system where the molecules of the lower layer are constrained to stand as stable tripods on a supporting surface free to rotate only about the axis normal to the surface. Although this system also has two branches, each with three transitions, the most significant aspect of its behavior is the extremely weak coupling between layers. Experimental data for the bilayer is discussed in the light of the structural predictions for the tripod bilayer.
A theoretical approach to the dielectric relaxation of liquid alcohols
Authors: Minami Ryuichi , Itoh Koichi , Takahashi Hiroaki , Higasi Keniti
Published: February 2003

The dielectric relaxation mechanism of liquid alcohols was studied by assuming the association equilibrium between hydrogen-bonded chain multimers. The dipole inversion arising from the cooperative rotation of the OH groups of the multimers was considered to be the main mechanism of the dipole relaxation. The stochastic model of one-dimensional random walk was introduced to explain the dipole inversion process and it was found that the dipole relaxation time of an n-mer is proportional to n+1. Based on this result and the stoichiometry of the association equilibrium, we calculated the dielectric constants and losses of liquid alcohols as a function of ω, which are in fair agreement with the experimental results.
Radiative and fragmentation decay of the cations of t
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s-1,3,5-hexatriene and of all t
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s-1,3,5-heptatriene in the Ã(π−1) states, studied by emission and photoelectron–photoion coincidence spectroscopy
Authors: Allan M. , Dannacher J. , Maier J. P.
Published: February 2003

Gas phase emission spectra of the cations of trans- and cis-1,3,5-hexatriene and of all trans-1,3,5-heptatriene have been obtained using ?25 eV electron impact as excitation. The band systems have been assigned as the ?(π−1)→?(π−1) electronic transitions according to the interpretation of their photoelectron spectra. An analysis of the emission bands yields several vibrational frequencies of the totally symmetric fundamentals for these cations in their ground states. These are compared to the frequencies obtained from the matrix absorption and photodissociation spectra of these cations for the ? states, and from the photoelectron spectra. The title cations in the ? states decay by radiative and fragmentation pathways, which are both detected. The fragmentation decays have been studied by photoelectron–photoion coincidence technique using He(Iα) photon radiation. In the case of the 1,3,5-hexatriene cations, C6H+8 and C6H+7 ions are detected on formation of the ? states, whereas for the all trans-1,3,5-heptatriene cation, in addition to the molecular ion, C7H+9, C6H+7, and C6H+6 fragment ions are also observed. Quantum yields of emission from the lowest vibrational level of the ? state of trans- and cis-1,3,5-hexatriene cations have been estimated as 7% and 0.3%, respectively, from the lifetime and relative emission intensity measurements, and the integrated extinction coefficients of the matrix absorption spectra. In order to explain the much larger branching ratios for the parent ions, and the ?20% deviation of the sum curves from unity obtained in the coincidence measurements, it is postulated that there are two nonradiative pathways for the lowest levels of the ? states. One leads to cyclic C6H+7 fragment ions via a cyclic C6H+8 precursor, whereas the other decay is to a linear vibrationally excited C6H+8 ion which cyclizes only slowly, at a rate <104 s−1. In the case of all trans-1,3,5-heptatriene cation the parent ion branching ratio (2.8%) is probably not much greater than the emission quantum yield.
Association reactions of C+ ions with H2 and D2 molecules at 78 and 300 K
Authors: Johnsen Rainer , Chen A. K. , Biondi Manfred A.
Published: February 2003

The association reactions of C+ ions with H2 and D2 molecules have been investigated using drift tube–mass spectrometer techniques. It is found that at H2 or D2 densities of ∼1×1016 cm−3 the reactions proceed by three-body association, with rate coefficients of (3±0.3)×10−29 cm6/s at 300 K and (6±0.6)×10−29 cm6/s at 78 K for H2, with slightly larger values for D2. The measurements also place an upper limit of k≲2×10−14 cm3/s at 300 K for the rate coefficient for radiative association C++H2→CH2++hν, a process thought to constitute an important step in the formation of molecules in interstellar gas clouds.
A fluorescence monitor method for measuring effective absorption coefficients of molecular rovibronic transitions using tunable dye laser excitation: The case of absorber linewidth narrower than the laser linewidth applied to H2CO
Authors: Fairchild Paul W. , Garland Nancy L. , Howard Willis E. , Lee Edward K. C.
Published: February 2003

A technique for measuring ’’effective’’ absorption coefficients is described. It circumvents deviations from Beer’s law caused when the excitation source bandwidth is larger than the absorber bandwidth. The technique employs a fluorescence cell placed after an absorption cell to selectively monitor absorption in the center region of the source line. Model calculations relating the fluorescence intensity to source and absorber line shapes indicate that this method should yield linear Beer’s law plots for moderate values of k0Nl and α, where α is the ratio of the source bandwidth to the absorber bandwidth. This technique has been applied to a number of single rotational levels in the 410 transition of the H2CO ? 1A2←? 1A1 system using pulsed, tunable dye laser excitation. The effective absorption coefficients determined experimentally have been compared to the theoretically calculated absorption coefficients.
Studies of protein–nucleic acid interactions by photon correlation spectroscopy. I. tRNA–BSA interactions at low ionic strength
Authors: Patkowski A. , Chu B.
Published: February 2003

Photon correlation measurements of tRNA–BSA association in 1 mM sodium cacodylate buffer are reported. In terms of the overall geometry of the reactants (tRNA and BSA) and their aggregates as well as the reaction rate constants, we have confirmed that, in tRNA–BSA solutions, the tRNA–BSA aggregates in the presence of an excess of BSA are twice as big as those in an excess of tRNA. Furthermore, the experimentally estimated association rate constant is two orders of magnitude lower than the one calculated for a diffusion controlled reaction without taking into account electrostatic interactions in solution. Thus, it is important to include long-range repulsive electrostatic interactions which tend to slow down the reaction markedly.
Quartet–doublet interactions observed in the emission spectrum of the NO molecule
Authors: Miescher E.
Published: February 2003

Emission bands, B 2Π–X 2Π (β-bands), of the NO molecule analyzed fifty years ago by Jenkins, Barton, and Mulliken are revisited. A large 4Σ−∼2Π interaction (H=5.1 cm−1), predictable by recent ’’anticrossing’’ and ’’electron-impact’’ experiments is detected. Additional smaller perturbations are studied. The aim to locate exactly the quartet states with respect to the doublet states is not fully achieved, but the energies of v=0 and 1 of the b 4Σ− state are determined to ±10 cm−1, and several rotational levels are located to ±0.1 cm−1. The sign of the Λ-doubling in the ground state is established.
Optoacoustic spectra of some molecular gases at CO2 laser wavelengths between 9 and 11 μm
Authors: Walzer K. , Tacke M. , Busse G.
Published: February 2003

With a conventional cw CO2 laser optoacoustic spectra of several molecules have been measured at laser wavelengths between 9 and 11 μm. The molecules are: trichloroethylene (C2HCl3), chlorotrifluoromethane (CClF3), tetrachloromethane (CCl4), dichloromethane (CH2Cl2), 2-propanol (C3H8O), triethylamine (C6H15N), tripropylamine (C9H21N), water, diethyl ether (C4H10O), acetaldehyde (C2H4O), and formaldehyde (CH2O).
Vibration–rotation line shifts for 1Σg+ H2 (v, J)–1S He computed via close coupling: temperature dependence
Authors: Hahne G. E. , Chackerian C.
Published: February 2003

The density-shifting of vibration–rotation transitions of H2 perturbed by He was computed (as a function of temperature) with no adjustable parameters. The calculation was carried out using the framework of the impact theory of Baranger with S-matrix elements obtained via close-coupling calculations which incorporated the ab initio H2–He system potential of Tsapline, Kutzelnigg, Raczkowski, and Lester [Chem. Phys. Lett. 47, 45 (1977)]. Vibrational and rotational inelasticity were neglected in the calculations; nevertheless good agreement with experimental data was obtained, up to moderate temperatures, for the density shift. A much poorer comparison was obtained for the density broadening.
The effect of the parity violating electron–nucleus interaction on the spin–spin coupling Hamiltonian of chiral molecules
Authors: Harris Robert A. , Stodolsky Leo
Published: February 2003

We show that the form of the parity violating electron–nucleus interactions permits construction of an additional contribution to the effective spin–spin coupling Hamiltonian in spin multiplet states of chiral molecules. The ratio of the difference of the zero field splittings of optical isomers to the unperturbed zero field splitting is estimated to be 105 as large as the optical frequency ratios which have previously been investigated.
Asymptotic behavior of atomic Hartree–Fock orbitals
Authors: Handler George S. , Smith Darwin W. , Silverstone Harris J.
Published: February 2003

The restricted Hartree–Fock equations are solved at large r for closed shell atomic states. Except for states containing only s orbitals, the Hartree–Fock orbitals obey the formula, φi(r)∼kiYlimi(ϑ,φ) rβ−λ−1 exp(−ζr), where −1/2ζ2=εho, the highest occupied orbital energy, where β= (nuclear charge – number of electrons +1−ζ)/ζ, where λ+1=0 for the highest occupied orbital, where λ=‖ li−lho ‖ if li≠lho, where λ=2 if li=lho≠0 and i≠ho, where λ=2lmin+1 if li=lho, and where lmin is the smallest nonzero l value of the occupied Hartree–Fock orbitals.
Polarized Raman spectra of n-alkane single crystals with orthorhombic polyethylene-type sublattice
Authors: Kobayashi Masamichi , Tadokoro Hiroyuki , Porter R. S.
Published: February 2003

Polarized Raman spectra were measured on single-crystal specimens of orthorhombic n-C35H72 and monoclinic n-C36H74, both consisting of the orthorhombic polyethylene (o-PE) subcells. Relative magnitudes of the squared elements of the derived polarizability tensor were evaluated for every zone-center fundamentals of the o-PE lattice. These values were proved to reproduce well the observed Raman intensities of uniaxially oriented and unoriented samples of PE. The polarizations, the frequencies, and the intensity ratios of the components of the doublets due to the crystal-field splitting were measured for all the internal modes except for the CH2 stretching vibrations, using a single-crystal specimen of n-C35H72 cooled at liquid helium temperature. They agreed with the results of the normal coordinate treatment of the o-PE lattice. The Raman activity of the B3g component of the CH2 rocking mode was found to vanish as predicted by the oriented-gas model approximation.
Solid-state synthesis of highly conducting polyphenylene from crystalline oligomers
Authors: Shacklette L. W. , Eckhardt H. , Chance R. R. , Miller G. G. , Ivory D. M. , Baughman R. H.
Published: February 2003

Paraphenylene oligomers (biphenyl, p-terphenyl, p-quaterphenyl, p-quinquephenyl, p-sexiphenyl) form electrically conducting complexes with AsF5. Prolonged exposure to AsF5 causes a polymerization of these p-phenylene oligomers to give highly conducting charge-transfer complexes of poly(p-phenylene). Conductivities as high as 50 S/cm have been measured. Powders, thin films, and single crystals of p-phenylene oligomers have been reacted with AsF5. The undoped oligomers and the doped, compensated, and annealed products have been investigated by means of x-ray diffraction, and UV-visible and IR transmission spectroscopy. The x-ray diffraction studies give evidence for a change in lattice spacings to those characteristic of the crystalline polymer. The spectroscopic measurements during AsF5 doping reveal shifts in absorption bands in the UV and the IR to those characteristic of poly(p-phenylene). Paraoligophenylenes have also been reacted with elemental potassium in THF solution with trace amounts of naphthalene. Highly conducting complexes were formed (0.5 S/cm for sexiphenyl) but there is no evidence for further polymerization.
Mass spectrometric determination of partial electron impact ionization cross sections of He, Ne, Ar and Kr from threshold up to 180 eV
Authors: Stephan K. , Helm H. , Märk T. D.
Published: February 2003

A new approach to mass spectrometric measurement and analysis has been used to study the electron impact ionization of the rare gases in the low electron energy regime (<180 eV). Critical considerations are given to the problems of ion extraction from the ion source (Nier-type) and the transmission of the extracted ions through the mass spectrometer system (double focusing sector field Varian MAT CH5). Accurate relative partial cross section functions were obtained for production of He+ and He2+ from He; Ne+, Ne2+, and Ne3+ from Ne; Ar+, Ar2+, Ar3+ from Ar, and Kr+, Kr2+, Kr3+ and Kr4+ from Kr. In addition, the cross section ratios for the partial ionization cross sections of each individual gas were determined. These ratios were used to sum up the relative partial cross section functions for each gas, hence obtaining relative total ionization cross section functions by weighting each partial cross section function with the respective charge number. The shape of the relative total ionization cross section function thus obtained was compared with ionization tube measurements of the total ionization cross section curve. Good agreement with the data of Rapp and Englander-Golden was found. This comparison allows the normalization of the measured relative partial cross section functions, yielding absolute partial cross section values for all of the processes mentioned above. The experimental results presented are compared with previous determinations where available.