bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploiting the isomorphism between quantum theory and classical statistical mechanics of polyatomic fluids
Authors: Chandler David , Wolynes Peter G.
Published: February 2003

From a discretization of the path integral formulation of quantum mechanics, it is possible to relate equilibrium quantum many body theory to classical statistical mechanics. In this paper, we significantly extend and analyze this well known isomorphism in terms of the equilibrium theory of classical molecular fluids composed of flexible polyatomic species. We show how quantum influence functionals are isomorphic to classical cavity distribution functions. The former describe the influence of surrounding media on the dynamics of quantal degrees of freedom, and the latter describe environmental effects for classical models of flexible molecules and chemical equilibria. The connection allows the use of classical theories to perform nonperturbative calculations of influence functionals which treat the influence functionals and many body correlation functions in a self-consistent fashion. We illustrate the computational advantages of the method by studying its predictions for a hard sphere model of liquid helium above the l transition. The nature of quantum indistinguishability of identical particles (i.e., quantum exchange) is treated in our theory in terms of an exact isomorphism with chemical equilibria. This connection allows the treatment of exchange in condensed phases in terms of the classical law of mass action, and provides a computational advance over existing methods for interacting systems. By picturing exchange in terms of classical association equilibrium, we arrive at a view (hinted at long ago by Feynman and by Penrose and Onsager) in which the Bose condensation is related to an equilibrium polymeric sol–gel transition. Thus, below the l transition, the correlations in liquid helium are equivalent to those in a classical fluid containing a finite concentration of macroscopic polymers. We stress how the path integral aspect of the isomorphism leads to useful geometrical interpretations of quantum phenomena. For example, tunneling phenomena can be viewed in terms of solitonic (or instantonic) configurations or flexible chain molecules. With this picture, we show how the isomorphism can be employed to understand both adiabatic and nonadiabatic solvent effects on chemical bonding. For concreteness, we provide a detailed analysis of a particular model of the chemical bond for which a partial summation over intermediate quantum paths leads to an Ising model problem in the isomorphism. While applications like this are presented in the form of qualitative illustrations, a variety of methods can be employed to produce quantitative results. We sketch how these calculations can be performed for various problems, making connections with methods like the renormalization group (RG) technique. The classical isomorphism together with the modern theory of classical polyatomic systems provides a powerful framework for quantitative solutions of condensed matter quantum mechanical problems.
A determination of the spin–rotation parameters for NO2 in the X̃ 2A1 state by microwave–optical double resonance
Authors: Brown J. M. , Steimle T. C. , Coles M. E. , Curl R. F.
Published: February 2003

Magnetic dipole transitions between the spin components of rotational levels of NO2 in its ground state have been observed by the technique of microwave–optical double resonance. Fluorescence induced by an argon ion laser was used to monitor the process. Observations were made in the range 4 to 12 GHz and provide information on levels with a wide spread of N and Ka values. The results have been used in conjunction with the known electric dipole transition frequencies and some recent data from radio frequency–infrared double resonance to determine the rotational and spin–rotational parameters for the molecule in its ground state. It has proved possible to determine all the three quadratic and six quartic parameters in the spin–rotational Hamiltonian. The improvement in knowledge of the spin–rotation intervals allow a refinement of the Zeeman parameters for NO2 by refitting the data from the EPR and LMR spectra. The results are in good agreement with the relationships gSaa = gS−eaa/2Baa, etc.
A 59Co NMR study of the magnetic shielding of the cobalt nucleus in cobalt (III) complexes
Authors: Juranić N.
Published: February 2003

The temperature dependence (in the range 0–90 °C) of the 59Co magnetogyric ratios and of the 1A1g→1T1g electronic transition wavelengths for six octahedral cobalt (III) complexes were measured. For each complex a linear correlation between 59Co magnetogyric ratios and the electronic transition wavelengths was obtained, in accordance with the prediction of ligand field theory. All the correlation lines are of the same origin, thus stating that the diamagnetic shielding term is weakly influenced by ligands. This enables determination of the value of the 59Co nuclear magnetic moment: m = (4.617±0.005)mN. The slope of the correlation line varies from one complex to another directly with the nephelauxetic ratio b35 of the complex considered. On this basis a more general correlation, between 59Co magnetogyric ratios and electronic transition wavelengths reduced by nephelauxetic ratio, is suggested. As a consequence, it may be expected that magnetochemical series of ligands in transition metal complexes is independent of the central ion.
Electron spin-lattice relaxation times of transient free radicals
Authors: Fessenden Richard W. , Hornak Joseph P. , Venkataraman Balu
Published: February 2003

The saturation recovery method has been used to measure the electron spin relaxation times of short-lived free radicals in solution. The radicals were produced by continuous in situ radiolysis with a 2.8 MeV electron beam (except for two cases where stable radicals were formed by air oxidation). The ESR spectrometer used broad-band amplification of the detected ESR signal (time constant of 100 ns) and signal averaging by means of a transient recorder and minicomputer. The magnetic field was stepped off the ESR line for alternate saturating pulses; the phase of the microwave saturating pulse could be changed by 180 ° to allow separation of the saturation recovery and free induction decay. The sensitivity was such that T1 values greater than 1 ms could be determined for samples of 1014 spins (i.e., 3×10−6 M radical in 50 mℓ) if the ESR linewidth was 100 mG and transient curves from 40 000 saturating pulses were averaged. Somewhat smaller values of T1 could be determined with higher radical concentrations. To achieve this sensitivity, it was necessary to use observing microwave powers which significantly perturbed the recovery signal so that an analysis in terms of an exponential decay of the ESR signal to the steady state value was not possible. Curve fitting of solutions to modified Bloch equations was used. Values of T2 were determined from the damping of Torrey oscillations. Values of T1 were determined for p-benzo-semiquinone anion (2.0), the 2,5-di-tert-butyl analog (11.5), ascorbate anion radical (2.3), chelidonic acid trianion radical (5.0), 1,2-dicarboxylvinyl radical (9), and H atoms (13.5), all values in ms and accurate to about ±10%. The radicals were produced in aqueous solution except for the semiquinones which were in ethanol. The values of T2 were similar to the corresponding T1 except for ascorbate radical and 2,5-di-tert-butyl-p-benzosemiquinone anion, where unresolved splittings made the apparent values smaller.
Raman spectroscopy of the superionic conductor pyridinium silver iodide (C5H5NH) Ag5I6, in the ordered phase
Authors: Toms D. J. , Scott J. F.
Published: February 2003

The Raman spectra of pyridinium silver iodide (C5H5NH)Ag5I6 have been obtained in the ordered D6 phase. The spectra exhibit seven modes characteristic of pyridinium rings as well as two broad external modes characteristic of low-frequency silver ion motion (97 and 32 cm−1). The external modes broaden and disappear as the second-order transition to a superionic phase at 323 K is approached from below.
Fluorescence detected linear dichroism. A new method for studies of molecular orientation in uniaxial systems
Authors: Johansson Lennart B.-Å. , Lindblom Göran , Nagvi K. Razi
Published: February 2003

A theoretical and experimental description of a new light spectroscopic method for determination of second rank order parameters is presented. The linear dichroism is obtained from the total fluorescent intensity, measured by using an integrating sphere. The method has been tested on a dichroic sample consisting of a stretched polymer film with an incorporated dye (2,2′-diethyl thiocarbocyanide iodide). The main advantages of using emitted light are the high sensitivity and selectivity. With the method described the molecular orientation of a fluorophore in a mixture of other absorbing chromophores may be studied. It is also suggested that the integrating sphere should be used in determinations of excitation spectra and for measurements of fluorescence detected circular dichroism.
Depolarized light scattering in dilute solutions of alkanes: A comparison of the bond additive and interacting atom approximations to the molecular polarizability
Authors: Keyes Thomas , Evans Glenn T. , Ladanyi Branka M.
Published: February 2003

The molecular polarizability of a few small alkane (4–10 bond) chains has been represented by (1) an interacting atom model (IAM), wherein the atoms are treated as isotropic point polarizabilities interacting by the dipole tensor; and (2) the bond additive approximation (BAA) in which each bond is assigned an axially symmetric polarizability tensor, and the total molecular polarizability is the sum of the individual bond values. For selected values of the gauche–trans energy difference (0.3 kcal/mole), the calculated mean anisotropy per backbone atom 〈g2〉/N increases linearly with N for the IAM and is essentially independent of N in the BAA. Orientational correlation functions have been determined for several second rank tensors characterizing the flexible chains using a modified version of Fixman’s Brownian dynamics programs. The orientational correlation functions displayed an effective nonanalytic decay for short times merging into an exponential for long times. Single particle correlation times for the IAM increased more rapidly with N than did those of the BAA. Relaxation of the end-to-end vector (actually its second rank analog) was found to be the slowest process, followed by the IAM and the BAA polarizabilities, and finally the fastest was a local rotational mode.
Study of sulfur-containing molecules in the EUV region. I. Photoabsorption cross section of SO2
Authors: Wu C. Y. Robert , Judge D. L.
Published: February 2003

Using synchrotron radiation as a continuum background, the absorption cross sections of SO2 have been measured using a double ionization chamber. The cross sections range from 10 to a maximum value of 56 Mb in the 175–760 Å region. A possible window resonance series was observed and tentatively assigned to a Ryberg series converging to the (6a1)−1 ion state. From the fluorescence excitation function the vibrational progressions of the SO+2 ? 2B2, ? 2A1, and ? 2B1 ion states have been measured and found in good agreement with those observed from photoelectron spectroscopy. The same correspondence between peaks in the fragment fluorescence excitation function and the photoelectron spectrum suggests that these ion states of SO2 are dissociative in nature.
A Rydberg transition in benzene in the condensed phase: Two-photon fluorescence excitation studies
Authors: Scott Thomas W. , Albrecht A. C.
Published: February 2003

The two-photon states of benzene lying 6 to 7 eV above the ground state are probed by polarized two-photon fluorescence excitation techniques. Dramatic changes in both the excitation spectrum and the polarization ratio are seen as the pure liquid is diluted in alkane solvents. A new two-photon resonance, not seen in the pure liquid, appears in the spectrum of dilute benzene solutions. The polarization behavior of this new feature as well as its sensitivity to solvent and temperature is interpreted in terms of a two-photon promotion of an electron from the e1g HOMO into the 3s Rydberg orbital of benzene in the condensed phase.
An angle resolved photoemission determination of the coordination of CO on the ZnO(0001) surface
Authors: McClellan M. R. , Trenary M. , Shinn N. D. , Sayers M. J. , D’Amico K. L. , Solomon Edward I. , McFeely F. R.
Published: February 2003

Angle resolved ultraviolet photoemission spectroscopy employing polarized He ii resonance radiation has been used to determine the bonding geometry of CO to ZnO(0001) at 80 K. Bound CO molecules are oriented perpendicular to the zinc-terminated surface forming a linear Zn–C–O complex. This result, along with earlier work on the ZnO(101̄0) surface, is explained by a concise and coherent model for CO chemisorption on ZnO surfaces. The role of defect sites for CO chemisorption is considered.
Observation of intracavity absorption of molecules in supersonic beams
Authors: Lambert Wm. R. , Felker P. M. , Zewail A. H.
Published: February 2003

Intracavity absorption studies of DMT and I2 are reported at rotational and vibrational temperatures of <0.1?K and 16?K, respectively.(AIP)
Infrared intensities: An MO study of the transferability of intensity parameters in normal paraffins
Authors: Galabov B.
Published: February 2003

Model MO calculations have been carried out on normal paraffins, to study the correlation between polar parameters of C-H bonds. (AIP)
Comparison of SAMO and a
b i
n
i
t
i
o model calculations for pyrazine
Authors: Duke B. J. , Collins M. P. S.
Published: February 2003

The simulated ab initio molecular orbital (SAMO) technique and the ab initio model calculation of Butkus and Fink are compared for the pyrazine molecule. Both methods construct the wave function of pyrazine from wave functions of smaller pattern molecules. The methods are complimentary in that the strengths of one are often the weakness of the other. The SAMO method gives good orbital energies which are not given by the ab initio model method, while the latter is more readily extended to the ionic protonated molecules.
Ozone and oxygen atom reactions with dimethylsulfide and methanethiol in argon matrices
Authors: Tevault D. E. , Mowery R. L. , Smardzewski R. R.
Published: February 2003

Ground state oxygen atoms, generated by visible photolysis of ozone, have been reacted with CH3SCH3 and CH3SH in argon matrices. For CH3SCH3, a stepwise addition to form DMSO and dimethylsulfone was observed. Methanethiol reactions with O atoms were more complex, leading to production of CH3SOH, CH3OSH, CH3S(O)H, and possibly CH3–SO2–H. These results are compared to the O+H2S reaction. The matrix results are also compared to gas phase studies where more extensive fragmentation has been observed, and inferences are drawn concerning the relative matrix deactivation rates of the highly energetic sulfide–oxygen-atom precursor complex.
Rotational and vibrational energy distributions of 16OH(X 2Π) and 18OH(X 2Π) produced in the reaction of O(1D) with H2O and H2 18O
Authors: Butler J. E. , Talley L. D. , Smith G. K. , Lin M. C.
Published: February 2003

Laser induced fluorescence measurements of the rotational population distributions for the 16OH(X 2Πi, v = 0, 1) products of the reaction of O(1D) with H2O and the 16OH(X 2Πi, v = 0, 1) and 18OH(X 2Πi, v = 0, 1) products of the reaction of O(1D) with H2 18O are presented here. The rotational and vibrational distributions of the 16OH formed in the normal isotopic abundance reactions were found to be close to those expected if the energy of the reaction is statistically distributed amongst all available product states. Isotopic labeling of the oxygen atom in the reactant water molecule demonstrated that the vibrational distribution of the new 16OH bond formed is significantly more energetic than the remaining 18OH bond, while the rotational distributions were similar. These results are interpreted as H atom abstraction (or stripping) dynamics predominating over O atom insertion into the water OH bonds.
Semiclassical evaluation of inclusive transition probabilities
Authors: Möhring K. , Smilansky U.
Published: February 2003

We develop a semiclassical description for reactions of complex particles based on Feynman’s influence functional method. We study inclusive transition probabilities corresponding to a situation where only a set of collective variables is specified in the initial and the final states, for instance, inclusive angular distributions. We show that the inclusive probabilities can be expressed in terms of classical trajectories and derive proper equations of motion. We discuss to what extent interference phenomena appear, and present a uniform approximation for the description of focusing phenomena.
Photoexcitation and ionization in ozone: Stieltjes–Tchebycheff studies in the separated-channel static-exchange approximation
Authors: Padial N. , Csanak G. , McKoy B. V. , Langhoff P. W.
Published: February 2003

Theoretical studies are reported of total and partial-channel photoexcitation/ionization cross sections in ozone employing Stieltjes–Tchebycheff (S–T) techniques and the separated-channel static-exchange approximation. As in previously reported investigations of excitation and ionization spectra in diatomic and polyatomic molecules employing this approach, vertical electronic dipole transition spectra for the twelve occupied canonical Hartree–Fock symmetry orbitals in ozone are constructed using large Gaussian basis sets, appropriate computational methods, and noncentral static-exchange potentials of correct molecular symmetry. Experimental rather than Koopmans ionization potentials are employed when available in construction of transition energies to avoid the incorrect ionic-state orderings predicted by Hartree–Fock theory, and to insure that the calculated series have the appropriate limits. The spectral characteristics of the resulting improved-virtual-orbital discrete excitation series and corresponding static-exchange photoionization continua are interpreted in terms of contributions from valencelike 7a1(σ*), 2b1(πx*), and 5b2(σ*) virtual orbitals, and appropriate diffuse Rydberg functions. The 2b1(πx*) valence orbital apparently contributes primarily to discrete or autoionizing spectra, whereas the 7a1(σ*) and 5b2(σ*) orbitals generally appear in the various photoionization continua. Moreover, there is also evidence of strong 2p→kd atomiclike contributions to ka2 final-state channels in the photoionization continua. The calculated outer-valence-shell 6a1, 4b2, and 1a2 excitation series are compared with electron impact–excitation spectra in the 9 to 13 eV interval, and the corresponding partial-channel photoionization cross sections are contrasted and compared with the results of previously reported studies of photoionization in molecular oxygen. The intermediate- and inner-valence-shell excitation series and corresponding photoionization cross sections are in general accord with quantum-defect estimates and with the measured electron-impact spectra, which are generally unstructured above ∼22 eV. Of particular interest in the intermediate-valence-shell spectra is the appearance of a strong σ→σ* feature just above threshold in the 3b2→kb2 photoionization cross section, in qualitative agreement with previously reported studies of the closely related 3σg→kσu cross section in molecular oxygen. Finally, qualitative comparisons are made of the calculated K-edge excitation and ionization spectra in ozone with recently reported photoabsorption studies in molecular oxygen.
The hydrogen atom and the H+2 and HeH++ molecular ions inside prolate spheroidal boxes
Authors: Ley-Koo E. , Cruz S. A.
Published: February 2003

We formulate the exact solution of the Schrödinger equation for systems of one electron in the Coulomb field of one or two fixed nuclei at the foci inside prolate spheroidal boxes. Numerical results are obtained for the energy eigenvalues and eigenfunctions of the lowest states of the hydrogen atom and the H+2 and HeH++ molecular ions for boxes of different sizes and eccentricities. We also evaluate the hyperfine splitting of atomic hydrogen and of H+2.
Torsional photoisomerization of substituted ethylenes: Application to stilbene
Authors: Knauss D. C. , Evans G. T.
Published: February 2003

The trans to cis isomerization rate of stilbene is determined using a diffusional model for internal rotation. It is found that the rate is sensitive to the structural model for stilbene adopted and factors of 2 can be introduced by assuming the phenyl substituents are spherical. The preferred model treats the phenyl substituents as collections of six spheres rigidly bound together and having a specific pitch angle with respect to the plane of the ethylene double bond. The use of a model potential function, chosen to agree qualitatively with experimental findings, allows the calculation of the isomerization rate as a function of the height of the barrier to rotation Q. The experimental value for the rate can be fit with this model using a barrier height ranging from 2–3 kcal/mole, in accord with previous estimates.
Electrical transport in europium and gadolinium ferrocyanides
Authors: Tennakone K. , Kaluarachchi D. , Ariyasinghe W. M.
Published: February 2003

Europium(III) and gadolinium ferrocyanides are found to be conductors of electricity. The temperature variation of the resistivity of europium(III) and gadolinium ferrocyanides is studied.
Inhibition of water condensation by a soluble salt nucleus
Authors: Williams Richard , Blanc Joseph
Published: February 2003

In heterogeneous condensation of water vapor on an insoluble solid surface, the presence of a soluble salt crystal has two effects. The first is the well-known effect as a nucleus for condensation at low supersaturation. We show that it also inhibits condensation around it by reducing the concentration of adsorbed molecules. This effect extends to macroscopic distances.
Effect of temperature and hydrostatic pressure on the Raman active internal and external modes of 1,3,5-trinitro-1,3,5-triazocyclohexane
Authors: Owens F. J. , Iqbal Z.
Published: February 2003

The effect of temperature and hydrostatic pressure up to 30 kbars on the Raman active internal and external vibrational modes of solid 1,3,5-trinitro-1,3,5-triazocyclohexane has been measured. Mode Grüneisen parameters have been calculated. The effect of pressure and temperature on the mode frequencies have allowed a separation of the implicit and explicit contributions to the temperature dependence of the vibrational frequencies of the lattice modes. The results indicate an unusually large explicit contribution for a molecular crystal, suggestive of covalent bonding between the molecules of the lattice. The CH2 symmetric stretching vibration of the molecule showed an atypically large pressure dependence for an internal molecular mode, having a slope 30% larger than the most pressure dependent lattice mode.
Codeposition generation of BeCl in an argon matrix at 12 K: An ESR investigation
Authors: Knight Lon B. , Wise Marcus B. , Childers A. G. , Daasch W. R. , Davidson E. R.
Published: February 2003

The molecular radical BeCl has been produced by the codeposition of beryllium atoms and chlorine in an argon matrix at 12 K. An ESR investigation yields the following magnetic parameters: g∥ = 2.001 (1), g⊥ = 1.998 (1), A∥(Be) = 282 (2) MHz, A⊥(Be) = 268 (2) MHz, ‖A∥‖(35Cl) = 53 (2) MHz, and ‖A⊥‖(35Cl) = 24 (2) MHz. Spin densities obtained from the ESR results are compared with ab initio calculations. The calculations yield a dipole moment of 1.0 D for BeCl. These results for BeCl are compared with BeF, BeOH, and BeH. BeCl, unlike BeF, does not exhibit rotational behavior in an argon matrix.
Double resonance and high resolution infrared spectroscopy of the CF4 ν3 fundamental. II. Infrared–microwave double resonance and infrared Q-branch spectrum
Authors: Takami Michio
Published: February 2003

Pure rotational transitions between the v3 = 1 Coriolis sublevels of CF4 were observed by infrared–microwave double resonance. A frequency tunable semiconductor diode laser was used as a pumping radiation source. 117 microwave transitions in the JJ+1–JJ, J+1J+1–JJ, JJ–J−1J, JJ–JJ−1, and J+1J–JJ branches were measured within the accuracy of a few tens of kHz. Transitions in the last two branches showed a large systematic frequency shift caused by perturbations fom the 2ν4 state. The observed pure rotational spectrum was analyzed including the previously measured radio frequency transitions. About 200 infrared ν3 Q-branch absorption lines, which were assigned by infrared–radio frequency double resonance, were also analyzed. Eight tensor and nine scalar constants were tentatively determined, including the three ground state constants B0, D0, and D0(4q4).
Vibrational correlation-function modeling in the context of the Zwanzig–Mori formalism. Application to liquid ethane
Authors: Wilde Richard E.
Published: February 2003

The relationship between the memory-function approach to correlation-function modeling and the Mori continued-fraction scheme suggests that unsuspected dynamical couplings may require higher-order procedures to adequately model some correlation functions. The application of first-, second-, and third-order memory-function procedures and their significance is discussed. Some guidelines for the experimentalist are given, and the problem of the truncation of isotropic Raman bands is discussed. The spontaneous Raman-scattering spectrum of the ν3 band of C2H6 has been reexamined for sample temperatures in the range 93–168 K. Both the isotropic and anisotropic spectra have been obtained, and the vibrational-correlation function has been modeled within experimental error. The need to go to third order in the modeling procedure and the values of the second moments of the IVH spectra suggest a vibrational–rotational coupling. The depolarization ratio for the ν3 band was observed to be 0.21.
Half-collision description of final state distributions of the photodissociation of polyatomic molecules
Authors: Band Yehuda B. , Freed Karl F. , Kouri Donald J.
Published: February 2003

The full three-dimensional quantum mechanical scattering equations, describing direct photodissociation and weak predissociation from initially selected levels, are analyzed within a formulation which permits the use of the different nuclear coordinate systems appropriate to the bound and dissociative surfaces. The coupled two surface scattering equations satisfy the physical boundary conditions of regularity at the origin and purely outgoing flux on the dissociative surface (with incoming photon flux.) These equations are transformed, both in integral and differential equation forms, into single surface half-collision equations wherein the initial bound state wave function, multiplied by the appropriate coupling operator, is propagated on the dissociative surface with the physical boundary conditions. These driven equations are shown to yield transition amplitudes which are equivalent to the transition amplitudes obtained from the Gell-Mann and Goldberger (GMG) scattering formulation which employs plane wave plus purely incoming wave eigenfunctions to evaluate the transition amplitudes. Given the direct transition amplitudes evaluated for the full three-dimensional case by Morse et al., the scattering equations may be integrated along the reaction coordinate, and the full state-to-state photodissociation amplitudes are obtained from the asymptotic limit of the driven single surface equations. Although the driven equation formulation is applicable to molecules of arbitrary size, the theory is presented specifically for the case of photodissociation of a triatomic molecule, the case for which a full three-dimensional calculation is most feasible. The GMG formulation is utilized to enable the application of standard scattering approximations to the single surface driven half-collision equations. The cases of the coupled states and the infinite order sudden approximations are treated in detail along with a discussion of some of the conditions of their applicability.
A simple classical model of infrared multiphoton dissociation
Authors: Ramaswamy Ramakrishna , Siders Paul , Marcus R. A.
Published: February 2003

The classical mechanics of a system of two nonlinearly coupled oscillators driven by an oscillating electric field is studied. The presence of quasiperiodic and chaotic motion in the unforced system is shown to influence the nature of energy absorption. Two essentially different types of behavior are observed. In the first, energy is exchanged in a multiply periodic manner between the system and the forcing field. In the second regime, the energy exchange is erratic and a statistical analysis of a family of trajectories shows the role of the chaotic motion in the unforced system in the dissociation process. A theory for rate of photodissociation is presented and results are compared with those obtained from an ensemble of exact classical trajectories.
A critical binary liquid in an electric field
Authors: Beaglehole D.
Published: February 2003

The effects of an electric field on a critical binary liquid mixture cyclohexane–aniline have been studied via the adsorption at the liquid–vapor interface. The liquid partially filled the space between two electrodes, and shifts in the critical temperature depended upon the orientation of the electric field. A model for the liquid–vapor interface presented recently is generalized to include the effects of an electric field, and comparison with the experimental results suggests that the liquid dielectric constant shows critical behavior.
Further development of the approach of Peralta and Zwanzig. I. The drag on a sphere at high bath densities
Authors: Keyes T. , Morita Terumitsu , Mercer John
Published: February 2003

A simple analytical calculation is given for the drag on a ’’center of force’’ in a fluid flowing at infinity, following the approach of Peralta and Zwanzig. For infinite ramp and step potentials, we reproduce their results with new techniques which greatly simplify the calculation. We discuss the reason why the method does not give Stokes’ law, and we present a reasonable approximate method which does give Stokes’ law.
On CC, CS, and IOS generalized phenomenological cross sections for atom–diatom mixtures
Authors: Fitz D. E. , Kouri D. J. , Evans D. , Hoffman D. K.
Published: February 2003

Close coupled expressions for phenomenological cross sections which describe transport properties of atom–diatom mixtures are obtained in the total-J coupling scheme and are related to the bracket integrals of kinetic theory. Coupled states and infinite order sudden expressions for the generalized phenomenological cross sections using initial, final, and average l-labeling are also given. Particular care is taken to use a phase convention for the CS and IOS approximations which is consistent with the Arthurs–Dalgarno formalism and which gives the correct behavior of degeneracy averaged differential cross sections.
The influence of rotational changes on the quantum number scaling of vibrationally inelastic rate constants
Authors: DePristo Andrew E.
Published: February 2003

A general formula is presented, based upon the energy corrected sudden scaling theory, which describes the variation of rotationally equilibrated vibration-to-translation relaxation rates with initial vibrational state. The influence of each rotational quantum number change on the vibrational scaling is explicitly displayed. This result allows for a detailed investigation of the possible role of rotational transitions on the vibrational relaxation in HF and DF upon collisions with structureless particles. Application to the HF–HF system yields the separate V–T and V–V relaxation rates in different vibrational levels.
Quantum and classical dynamics of a coupled double well oscillator
Authors: Christoffel Kurt M. , Bowman Joel M.
Published: February 2003

We consider the effect of coupling in a model, two mathematical dimension isomerization reaction. The isomerization is described by a symmetric double well potential and the other degree of freedom is a harmonic bond. The time evolution of the reaction is studied in detail by a variety of quantum and classical mechanical methods. We consider first and second order quantum perturbation theory, self-consistent field theory, self-consistent field-configuration interaction theory, and vibrationally adiabatic theory. Classically, we consider exact trajectories and approximate ones based on a quantized vibrationally adiabatic theory. The effect of vibrational excitation of the harmonic degree of freedom on the isomerization rate is investigated as is the extent to which quantum and classical descriptions of this effect differ. We point out two quantum effects in this model system and note that one is due to the coupling between the two degrees of freedom. This effect has not been previously reported; however, it could be a general feature of state selected isomerization reactions.
Calculation of reaction probabilities and rate coefficients for collinear three-body exchange reactions using time-dependent wave packet methods
Authors: Agrawal P. M. , Raff L. M.
Published: February 2003

Wave packet methods are described that permit rate coefficients for the collinear A+BC exchange reaction to be obtained directly without the necessity of computing the reaction probabilities out of all statistically significant initial BC vibrational states. Similar wave packet methods are given that allow reaction probabilities at essentially fixed energy for collinear A+BC systems to be computed by time-dependent methods. The explicit integration procedure of Harmuth is utilized to evolve the wave packets. The methods are appplied to reactions occurring on three different LEPS-type potential-energy surfaces using the hydrogen atom mass for each atom and also to the T+HD→TH+D reaction on a realistic potential-energy surface. In most cases, the results are shown to be in excellent accord with exact close-coupling calculations.
Efficient multiphoton dissociation of CF3I+ in the metastable X̃ 2E1/2 excited state using cw infrared laser radiation
Authors: Thorne L. R. , Beauchamp J. L.
Published: February 2003

Evidence for the multiphoton dissociation of an electronic metastable state of CF3I+ with CO2 laser radiation is presented. Only those ions possessing sufficient internal excitation before irradiation can be dissociated. Photodissociation results primarily from resonant absorption by the ν1 vibrational mode of CF3I+ in the higher of the two, spin–orbit levels of the ground electronic state ? 2E1/2. Only the lowest energy decomposition channel is observed; this yields CF+3 and I. Spin–orbit and vibrational relaxation compete with photodissociation. At CF3I pressures below 2×10−7 Torr, the collisional relaxation rate is proportional to CF3I pressure kc = (3.1±0.4)×10−9 cm3 molecule−3 sec−1 with a zero pressure rate of 11.3±1.3 sec−1. The latter rate sets an upper limit on the spin–orbit relaxation rate. The photodissociation probability varies with laser frequency, exhibiting a broad, structureless peak near 960 cm−1. The initial photodissociation rate is proportional to laser irradiance kD = 0.80±0.08 sec−1/W cm−2. The photoproducts and laser frequency dependence are the same using either cw or pulsed irradiation. Ions were exposed to irradiances up to 120 W cm−2 cw and fluences up to 1.6 J cm−2 pulsed. Ion cyclotron resonance (ICR) techniques were used to store and detect the ions.
Vibrational distributions of HgBr(B 2Σ) and HgI(B 2Σ) molecules formed by photodissociation of HgBr2 and HgI2
Authors: McGarvey John A. , Cheung Nai-Ho , Erlandson Alvin C. , Cool Terrill A.
Published: February 2003

Reliable fluorescence spectra (±3%) of HgBr and HgI photofragments formed in the direct photodissociation of HgBr2 and HgI2 at 193 nm have been measured. The nascent vibrational distributions of HgBr(B 2Σ) and HgI(B 2Σ) have been determined. The distributions are resolvable into the relative contributions from two processes: (1) hν+HgX2→HgX(B 2Σ) +X(2P3/2) and (2) hν+HgX2→HgX(B 2Σ)+X(2P1/2). HgX(B 2Σ) molecules formed with X(2P3/2) atoms exhibit vibrational population inversion and preferential energy disposal among the higher vibrational states. In contrast, the vibrational excitation of HgX(B 2Σ) molecules formed with X(2P1/2) atoms produces a Boltzmann-like distribution which strongly favors the lowest vibrational states.
A study of the metastable and long-lived Rydberg fragments resulting from electron impact on NH3
Authors: Carnahan Byron L. , Kao Wen-Wei , Zipf Edward C.
Published: February 2003

The production of long-lived, excited fragments following electron-impact dissociation of ammonia has been investigated using the technique of translational spectroscopy. Over an impact energy range from threshold to 200 eV, the dominant species observed were hydrogen 2s and Rydberg atoms. Through extensive time-of-flight and excitation function measurements of these fragments, five dissociation channels were found to contribute to the production of the H(2s) atoms, while the H(RYD) signal was found to consist of hydrogen atoms resulting from at least four distinct processes. Threshold and kinetic energy measurements show that for most of these processes a substantial amount of the bombarding electron’s energy is channeled through the unobserved product or products of the dissociation. In addition to the hydrogen features, a low intensity group of fragments which we believe are long-lived nitrogen Rydberg atoms was identified in the time-of-flight spectra. Excitation function measurements indicate that two dissociation channels contribute to the production of these fragments. When possible, the present results are compared to previous measurements of the dissociative excitation and ionization of ammonia.
On the theoretical determination of molecular first hyperpolarizability
Authors: Lazzeretti Paolo , Zanasi Riccardo
Published: February 2003

Coupled Hartree–Fock perturbation theory has been applied to evaluate the first hyperpolarizability in the molecules H2O, NH3, CH4, and CO. A group-theoretical approach has been employed, which makes it possible for a reduced file of symmetry distinct two-electron integrals to be processed at each iteration with reduced computer efforts. Several very large basis sets, including up to 4f functions on the heavy atom and 3d on hydrogen, have been retained, which yield SCF energies, dipole moments, polarizabilities, and first hyperpolarizabilities very near to the corresponding HF quantities. Except in the case of CO, large discrepancies with respect to experimental data have been found.
Formic acid chemiluminescence from cryogenic reaction between triplet methylene and oxygen
Authors: Lee Yuan-Pern , Pimentel George C.
Published: February 2003

Matrix samples of CH2N2/O2/Ar were photolyzed at 8 °K. Subsequent slow warming produced the previously observed O2  A′ 3Δu→X 3Σg− thermoluminescence and two new progressions, one at 3100–3600 Å and one at 3900–4900 Å. With 18O2, the 3100–3600 Å progression displayed isotopic shifts that allow two possible v″ vibrational assignments to give ν00 = 34 730 or 33 340 (±40) cm−1 and ωe″ = 1390±15 cm−1. Similarly, the 18O2 shifts in the 3900–4900 Å progression lead to two possible v″ assignments to give ν00 = 26 230 or 25 100 (±60) cm−1 and ωe″ = 1124±40 cm−1. These spectroscopic parameters point to assignments of the a3A″→X 1A′ and A′ 1A′→A 1A″ transitions of HCOOH for the 3100–3600 and 3900–4900 Å progressions, respectively. These are the first observations of such transitions of formic acid and are attributed to the CH2(3B1)+O2(3Σg−) reaction in the cryogenic matrix.
An interacting segment model of molecular electric tensor properties: Application to dipole moments, polarizabilities, and hyperpolarizabilities for the halogenated methanes
Authors: Miller C. K. , Orr B. J. , Ward J. F.
Published: February 2003

A previously developed interacting segment model [ISM—see J. Chem. Phys. 67, 2109 (1977)] is applied to a full-scale treatment of the electric dipole moments, isotropic and anisotropic polarizabilities, and hyperpolarizabilities of a series of 12 halogenated methane molecules CXnY4−n(X,Y = H,F,Cl; n = 0–4). The ISM scheme enables the molecular properties considered to be fitted in terms of a set of ’’bare’’ electric tensor parameters for each bond, which are modified (’’dressed’’) by intramolecular electrostatic interactions. The computed results of the ISM scheme, and of a corresponding interaction-free bond additivity model, are discussed in relation to the following: choice of geometric and bond parameters, quality of fit to experimentally determined molecular and bond properties, and predictive potential and general physical validity of the model. It is concluded that the ISM approach represents a substantial improvement over simple bond additivity as a basis for understanding molecular electric tensor properties.
Collision induced intramolecular vibrational energy transfer in 1B3u pyrazine
Authors: McDonald Daniel B. , Rice Stuart A.
Published: February 2003

Collision induced intramolecular vibrational energy exchange in 1B3u(n,π*) pyrazine was investigated by analyzing the pressure dependence of the emission from 10 prepared single vibronic levels. Energy transfer rates are, in general, lower than those previously observed in electronic excited states. Though the magnitude of the energy defect for a process strongly influences the transfer rate, other propensity rules are important. Among the single quantum changes possible, those involving mode 16b predominate. The vibronic coupling to the upper 1B2u (π,π*) state increases the observed rates dramatically.
The rotational spectrum, 14N-nuclear quadrupole coupling constants, and H,19F nuclear spin–nuclear spin coupling constant of the cyanogen–hydrogen fluoride dimer
Authors: Legon A. C. , Soper P. D. , Flygare W. H.
Published: February 2003

The microwave rotational spectra of four isotopic species of a linear dimer NCCN⋅⋅⋅HF formed between cyanogen and hydrogen fluoride have been observed and analyzed to give vibrational gound state rotational constants B0, centrifugal distortion constants DJ, the 14N-nuclear quadrupole coupling constants χ(1) and χ(2), and the H, 19F nuclear spin–nuclear spin coupling constants SHF as follows:                             It is shown that χ(1)−χ(2), which is necessarily zero in free cyanogen, arises from electrical changes rather than zero-point vibrational changes that accompany dimer formation. The part of this quantity assigned to polarization of cyanogen by hydrogen fluoride is interpreted on the basis of the Townes–Dailey model in terms of a transfer of ∼0.02e from N(1) to N(2) when HF approaches the latter atom along the molecular symmetry axis to form the dimer.
Fluorescence excitation spectra, lifetimes, and quenching of S2(B 3Σu−) in the wavelength region 280–315 nm
Authors: Quick C. R. , Weston Ralph E.
Published: February 2003

Fluorescence lifetimes have been determined for S2 vapor excited to the B 3Σu− state at wavelengths in the range 280–315 nm, with a spectral resolution of ∼0.5 cm−1. For states with v′⩽8, excitation in the bandhead region leads to fluorescence lifetimes of ∼30–45 ns. In addition, low-intensity peaks with much longer lifetimes are observed throughout the absorption spectrum. The decreased intensity and increased lifetime are attributed to perturbations by the B′ 3πu state. For the v′ = 9 state, lifetimes generally decrease as the excitation wavelength moves away from the bandhead and at some wavelengths a double exponential decay was observed. Although the v′ = 10 state is known to predissociate, weak fluorescence peaks with very short lifetimes (<3 ns) were observed. The addition of Ar as a quenching gas leads to complex fluorescence decay curves with two or three components for both v′ = 3 and v′ = 9 states. Lifetimes and quenching rate constants obtained in this work agree with those measured previously in this laboratory using a broad-band excitation source.
The evaluation of fitting functions for the representation of an O(3P)+H2 potential energy surface. I
Authors: Wagner Albert F. , Schatz George C. , Bowman Joel M.
Published: February 2003

The DIM surface of Whitlock, Muckerman, and Fisher for the O(3P)+H2 system is used as a test case to evaluate the usefulness of a variety of fitting functions for the representation of potential energy surfaces. Fitting functions based on LEPS, BEBO, and rotated Morse oscillator (RMO) forms are examined. Fitting procedures are developed for combining information about a small portion of the surface and the fitting function to predict where on the surface more information must be obtained to improve the accuracy of the fit. Both unbiased procedures and procedures heavily biased toward the saddle point region of the surface are investigated. Collinear quasiclassical trajectory calculations of the reaction rate constant and one and three dimensional transition state theory rate constant calculations are performed and compared for selected fits and the exact DIM test surface. Fitting functions based on BEBO and RMO forms are found to give quite accurate results.
The visible spectrum of jet-cooled CF3NO
Authors: DeKoven Benjamin M. , Fung Kwok Hang , Levy Donald H. , Hoffland Lynn D. , Spears Kenneth G.
Published: February 2003

We have observed fluorescence excitation and dispersed emission spectra for the A←X transition of CF3NO cooled in a supersonic expansion. The analysis of these spectra provide torsional energy levels both for the excited electronic state in a staggered conformer and the ground state in its eclipsed conformer. There is no evidence for any other conformer. An energy level calculation of the torsional motion shows that a simple cosine potential having a threefold barrier almost fits the data, but that significant discrepancies remain. Approximate barrier parameters, within the constraints of a simple cosine, are ?3 = 202±10 cm−1 and F = 2.23±0.10 cm−1 for the ground state and ?3 = 533±30 cm−1 and F = 2.12±0.16 cm−1 for the excited state. We discuss evidence for the vibrational normal coordiantes being dependent on torsional level and point out some unexplained intensity anomalies observed in emission to levels above the barrier in the ground state.
Optical coherence properties of collective molecular systems: A comparison of the statistical and quantum approaches
Authors: Abram Izo I. , Hochstrasser R. M.
Published: February 2003

The formalism of collective (Dicke-like) states and operators is used to describe the relaxation of the initially prepared state of a material in the presence of a laser field. The material states are shown to be expressible as minimum uncertainty wave packets formed from those special collective states that couple with the radiation field. It is shown that these coherent states of matter exhibit all the features that are usually attributed to ensemble averages of two-level molecules in a conventional statistical picture. However, there are new features in the quantum mechanical model when there are correlations among the molecules in the ensemble. The loss of minimum uncertainty characteristics of the wave packet correspnds to the transverse (T2) relaxation of the statistical model. Different types of T2 processes can be defined corresponding to the decay of different orders of coherence of the wave packet. Only for the case that the system decays in all orders of coherence do the quantum and statistical results coincide. There is expected to be a transverse relaxation that preserves one or more orders of coherence. Experiments are suggested that can test these ideas. A particular case of the formalism of collective states applies to molecular crystals and it provides a quantum mechanical picture of the dephasing of molecular excitons in terms of orders of coherence analogous to the usual manner of describing states of the radiation field.