bluuebunny/crossref_metadata_2025 huggingface dataset:
On transition-state theory and the classical mechanics of collinear collisions
Authors: Pechukas Philip , McLafferty Francis J.
Published: February 2004

We consider classical transition-state theory of collinear atom-diatom reactions. There are (many) potential surfaces for which this theory is exact provided all trajectories with energy above some fixed value are disregarded; the energy cutoff of course depends on the surface. We develop a simple criterion for recognizing or constructing such surfaces, and discuss examples. We also show that if a surface has a proper transition state, as defined below, then transition-state theory is exact unless collision complexes exist.
Molecular reorientation in liquid chlorine
Authors: Obermyer R. T. , Jones E. P.
Published: February 2004

The 35Cl nuclear spin-lattice relaxation times have been measured in liquid chlorine from the melting point at 173°K to the boiling point at 243°K. The results give correlation times for molecular reorientation which are described in terms of a hydrodynamic model and a cell model for the liquid.
LCAO-MO-SCF calculations using Gaussian basis functions. X. AlLi-SCF results and implications for choosing configurations for configuration interaction calculations
Authors: Kaufman Joyce J.
Published: February 2004

Ab initio LCAO-MO-SCF calculations have been performed for the lowest 1Σ+ state of AlLi. The results give a potential curve indicative of a chemically bound species but with the ESCF minimum lying slightly above the sum of the comparable SCF energies of the separated atoms. Analysis of the probable correlation energy contributions and an estimate of their magnitudes leads to an estimate of −1.5 eV for the correlation energy contribution to the binding in AlLi. This should be sufficient to permit the AlLi species to exist. The Li in AlLi is electron deficient compared to the Li atom itself. An examination of population analysis results for unoccupied orbitals leads to interesting insight into which virtual orbitals will correlate certain specific electron pairs or certain of the occupied molecular orbitals. The relationship suggests a very logical and systematic method for helping to choose a priori the best truncated set of virtual orbitals for configuration interaction calculations.
Beam studies of the energy dependence of the reactions of tritium atoms with n-hexane, cyclopentane, n-butane, and 1-chlorobutane
Authors: LeRoy Rodney L. , Yencha Andrew J. , Menzinger Michael , Wolfgang Richard
Published: February 2004

The reactions of monoenergetic tritium atoms with simple alkanes and halocarbons have been studied in the 1–200 eV range by a molecular beam technique. Excitation functions σi (E) for the different reaction channels are derived from the product yields by a Kinetic Theory Analysis. It is found that: (1) T for H substitution cross sections (to form labeled parent alkanes) are similar for all alkanes studied (n-butane, n-hexane, cyclopentane, and cyclohexane): threshold at 1.5± 0.5 eV, a rapid rise to a maximum at 9–12 eV and 1–3 Å2 and a slow decline at higher energies. The asymptotic high energy parent yields correlate well with the degeneracy of the reaction path, a fact that further demonstrates the independence from structural details of T for H substitution for a single reaction path. (2) In the formation of degraded alkanes by C–C bond breakage, drastic structural dependence of the reaction cross section is found. (a) When the hydrogen atoms along a C–C bond are staggered, as in the thermodynamically stable conformation of most alkanes, the C–C bond is effectively shielded from direct attack by the hydrogen envelope, and the dominant mode of reaction consists of the sequence: H displacement followed by decomposition of energetic primary reaction products and stabilization of the fragment species. (b) When the hydrogens are eclipsed (as exemplified to a good approximation by cyclopentane in its thermodynamically stable half chair form), the C–C bond is exposed to direct attack by incoming T atoms, and direct alkyl displacement is facilitated. Direct alkyl displacement is a low energy process on our scale, with a threshold E0<1.2 eV, and with most of the reaction occurring below a few electron volts. At higher energies (E>4 eV), mechanism (a) takes over, since the products from (b) decompose. (3) T for Cl displacement in 1-chlorobutane occurs at higher average energies than H substitution. The cross section for the former process has an onset in the 1 eV region and goes through a maximum at ∼15 eV. The probability of displacing a Cl atom exceeds that for displacement of a given H atom by a factor of 2–3.
ESR linewidths in solution. VI. Variation with pressure and study of functional dependence of anisotropic interaction parameter, κ
Authors: Hwang James , Kivelson Daniel , Plachy William
Published: February 2004

Measurements have been made on the ESR linewidths of vandyl acetylacetonate (VOAA) in a number of nonhydrogen-bonded solvents. The X-band spectra were taken over a wide range of temperatures and at pressures ranging up to 4.5 kbar. The high pressure measurements were carried out in a high pressure bomb containing a slow-wave helix, instead of a resonant cavity, and a pair of 100 kHz modulation coils; the sample was placed in a Teflon holder which also surrounded the helix and could be sealed after the sample was deoxygenated. The reorientation correlation time τθ, is written as τθ=43π r03κ(η/kT), where η is the coefficient of shear viscosity, T the absolute temperature, r0 the hydrodynamic radius determined by translational diffusion experiments, and κ the anisotropic interaction parameter. κ is proportional to the ratio of the mean square intermolecular torques to the mean square intermolecular force where the interaction is between VOAA and solvent molecules. The values of κ determined from these experiments are independent of pressure, temperature, and density. However, κ varies from solvent to solvent and an analysis of the data indicates, but not unambiguously, that κ decreases with solvent size and it increases with solvent dipole moment. The results are compatible with a quasirotational diffusion model, with the assumption that the autocorrelation functions for intermolecular forces and torques have the same time dependence, and with the assumption that the dependence of torques on intermolecular separation is nearly equivalent to that of forces. The single adjustable parameter, κ, is sufficient to explain all the spectra at low (η/T) for a given solvent regardless of pressure and temperature, but at high values of (η/T) unexplained discrepancies between theory and experiment occur. A discussion of anisotropic diffusion is also given; however, the anisotropic contributions are probably negligible for VOAA.
Magnetic structure of NdZn2
Authors: Debray D. , Sougi M.
Published: February 2004

Neutron powder diffraction measurements reveal that NdZn2, having the body-centered orthorhombic crystal structure (CeCu2-type), undergoes magnetic ordering below 21 ± 1°K. The magnetic structure can be described by the composite of a sinusoidal transverse wave moment alignment polarized in the b axis direction and propagating along the c axis, and a ferromagnetic component along the b axis. The propagation wavelength and amplitude of the sinusoidal component at 4.2°K are, respectively, 2.35 in units of c and 1.7 ± 0.1 μB. The ferromagnetic component equals ∼ 0.7 μB. Results of magnetization measurements are consistent with the above findings.
Production of metastable singlet O2 photosensitized by NO2
Authors: Frankiewicz Theodore C. , Berry R. Stephen
Published: February 2004

Energy transfer from electronically excited NO2 to O2 has been studied. The NO2* is produced by irradiation with light having 7000 < λ < 4050 Å. Observations of light emission from O2(a1Δg, v′ = 0), O2(a1Δg, v′ = 1), and O2(b 1Σg+, v = 0) have been made, and from these measurements at various pressures, rates have been measured for production of O2(a 1Δg, v = 0) and O2(b 1Σg+, v = 0) by energy transfer from NO2*, for quenching of O2(b 1Σg+) by O2, NO2 and wall collisions, and for quenching of O2(a 1Δg, v = 0) by NO2. The efficiency for Δg1 production is 7.5% ± 2.5%, per collision quenching NO2*, and for Σg+1 production, 0.14% ± 0.02%. The Δg1 production efficiency reported here is considerably greater than our preliminary value of 1%. The metastable O2 generated in an urban atmosphere by energy transfer from NO2* is 1%–5% as effective as ambient O(3P) in initiating the oxidation of alkylated aromatic hydrocarbons and 0.1% or less as effective in the case of small, unsubstituted olefins.
Deuterium isotope exchange between carboxylic acids and hydrogen
Authors: Torre F. J. , Czuczak M. , Monse E. U.
Published: February 2004

The catalytic exchange of deuterium between carboxylic acids and hydrogen according to RCOOH(l) + HD(g)⇋RCOOD(l)+H2(g), where R=H or CH3, has been studied with the acids in the pure state at various temperatures, and in solutions of carbon tetrachloride at 25°C. The hydroxyl hydrogen of the acids is about 3–4 times more enriched in deuterium than the hydrogen gas. The measured isotope effects are discussed in terms of molecular force field calculations for formic and acetic acid.
Annihilation of positrons in hydrocarbons and halogenated hydrocarbons adsorbed on silica gel
Authors: Tumosa Charles S. , Wang Cherng-Maw , Ache Hans J.
Published: February 2004

Positron lifetime spectra of a series of hydrocarbons and halogenated aromatic compounds adsorbed on silica gel have been studied as a function of adsorbate concentration. The fact that the anomolous long lifetime component found in pure silica gel is not affected by adsorbate concentration up to 1.5–1.7 mmole/g SiO2 indicates that thermalized positronium cannot react chemically with these compounds. The decrease of the intensity of the long lifetime component with the adsorbate concentration can be interpreted in terms of positron capture by these compounds or by chemical reactions of highly energetic Ps atoms with the adsorbate molecules.
DW-variational study of collinear atom-diatom collisions
Authors: Koppel Lewis M. , Lin J.
Published: February 2004

Schwinger's variational principle in its fractional form is applied to the study of vibrational excitations in collinear atom-harmonic oscillator collisions. Trial wavefunctions used are those of distorted waves derived from distortion potentials based on (a) a free molecule approximation, (b) an internal average, and (c) an optical potential recently proposed by Roberts. It is found that for nearest neighbor transitions in most of the systems studied a simple variational treatment yields transition probabilities superior to those of a perturbation expansion such as the distorted-wave Born series.
Tables of collision integrals for the Barker-Pompe, Barker-Fisher-Watts, and Parson-Siska-Lee inert gas potentials
Authors: Neufeld P. D. , Aziz R. A.
Published: February 2004

This paper presents tables of collision integrals Ω(l,s)*, collision integral ratios, higher order correction factors for viscosity, thermal conductivity and diffusion, and the isotopic thermal diffusion factor for the Barker-Pompe, Barker-Fisher-Watts, and Parson-Siska-Lee potentials. These potentials could be quite accurate in predicting dilute gas transport properties of Ar, Kr, Xe, and Ne.
Generalized van der Waals theories for surface tension and interfacial width
Authors: Lovett Ronald , DeHaven Patrick W. , Vieceli James J. , Buff Frank P.
Published: February 2004

An exact relation between surface tension and the direct correlation function (DCF) for the inhomogeneous region is developed which may be viewed as an exact formulation of the van der Waals density gradient theory for inhomogeneous fluids. A reasonable approximation to the DCF is employed to obtain characteristic features of the interfacial density gradient over an extended temperature range. This theory predicts that the interfacial width increases as (1−T/Tc)−0.65 at the ``low'' temperatures considered, and these results are in good agreement with the corresponding predictions of our earlier capillary wave treatment of interfaces. Comparison is also made with the predictions of an alternate, exact van der Waals-like formulation which is obtained from the expression for surface tension in terms of the pair number density and the intermolecular force. A combination of the DCF formulation and the capillary wave theory provides the possibility of predicting both interfacial thicknesses and surface tension, a route also available from pair capillary wave theory. Numerical examples corresponding to argon at 90°K are given.
Theory of reactive scattering. VII. On the uncoupled channel operator equations for rearrangement
Authors: Kouri Donald J.
Published: February 2004

A variational principle is presented for the uncoupled channel operator integral equations and amplitude density function integral equations discussed in Paper I of this series. The functional employed is a generalization to rearrangements of one used in purely nonreactive scattering. The principle is employed to incorporate the possible use of correlation functions in order to treat the effects of closed channels and dissociative continuum states.
Crossed beams product angular distributions: MCl and MI from Ba, Sr, Ca, and Mg + ICl and BaCN and BaBr from Ba + BrCN
Authors: Mims Charles A. , Lin Shen-Maw , Herm Ronald R.
Published: February 2004

Primitive product angular distributions of MCl and MI from Ba, Sr, Ca, and Mg+ICI and of BaCN and BaBr from Ba+BrCN have been measured in a crossed beams apparatus employing an electron bombardment ionizer-massfilter detector unit. Product center-of-mass (c.m.) recoil angle and energy distributions have been fit to the measured laboratory (LAB) angular distributions by averaging the c.m.→LAB transformations over the (nonthermal) beam speed distributions. Both the MCl and MI c.m. product distributions from M+ICl are relatively insensitive to the identity of the attacking atom, except that practically no MgI is formed in the Mg reaction. Other product yield ratios are estimated as ∼2:1 for MCl:MI from ICl, ∼10:1 for BaCN:BaBr from BrCN. All of the reactions favor forward c.m. product scattering (i.e., MX scattered within 90° of the direction defined by the incident M), although the preference is especially weak in the Ba+BrCN→BaBr+CN reaction. For ICl reactions, MI are formed with broader c.m. cross sections and higher average product recoil energies, E′, than are MCl; average E′ values are ∼8–12 kcal/mole for MI+Cl and ∼3–5 kcal/mole for MCl+I. The results are compared with the features of the analogous alkali atom reactions and are discussed in terms of the likely structures of the intermediates.
Structure of water and carbon dioxide clusters formed via homogeneous nucleation in nozzle beams
Authors: Stein Gilbert D. , Armstrong James A.
Published: February 2004

A nozzle molecular beam is operated so as to optimize the molecular clustering in the free jet expansion. Continuous beams of carbon dioxide and water are sampled with an ionization gauge detector. The increased beam intensity under some operating conditions can only be attributed to clustering. A high energy electron beam of 39.5 keV is used to obtain Debye-Scherrer diffraction patterns from carbon dioxide and water clusters. The largest size clusters produced are solid and have the structure of the bulk material which is simple cubic for CO2 and diamond cubic for H2O. The average diameters for CO2 and H2O are 52±5 and 54±5 Å, respectively, corresponding to 1600 and 2600 molecules per cluster. The CO2 data are in agreement with other beam results and, to the authors' knowledge, these are the first data published on the structure of water clusters formed from the vapor phase via homogeneous nucleation. Based on the diffraction data the structure of clusters down to average sizes in the range of 300–450 molecules per cluster can be treated as bulk phase.
Application of the many-body Green's function formalism to the lithium atom
Authors: Reinhardt William P. , Smith Jeffrey B.
Published: February 2004

The techniques of many-body Green's function theory have been applied to the calculation of properties of the lithium atom. Using basis set expansion techniques and a second-order expansion of the self-energy, Dyson's equation was solved, and the first-order reduced density matrix and the first ionization potential for the lithium ground state were computed. The natural spin orbitals of s symmetry were in excellent argeement with those computed from wavefunctions. The ionization potential was within 0.01 eV of the exact experimental result.
Use of the CNDO method in spectroscopy. VIII. Molecules containing boron, fluorine, and chlorine
Authors: Kuehnlenz G. , Jaffé H. H.
Published: February 2004

An extension of CNDO/S calculations to compounds of B, F, and Cl is reported. Except for some small molecules, good results are obtained for transition energies and intensities.
Fine structure and hyperfine structure of ortho-H2 d(3p) 3Πu (v=0–3) via microwave optical magnetic resonance induced by electrons
Authors: Miller Terry A. , Freund Robert S.
Published: February 2004

Microwave Optical Magnetic Resonance Induced by Electrons (MOMRIE) has been observed for vibrational levels v = 0–3 of ortho-H2 in the d(3p) 3Πu state with rotational quantum number N = 1. The theory used to analyze the spectrum is essentially the same as that which has previously been applied to the metastable c(2p) 3Πu state, but several additions are also given. The theory, as previously, has been formulated in terms of a representation in which the angular momenta are all coupled. However, a semi-quantitative formulation in terms of an entirely decoupled representation (which is more nearly appropriate for the MOMRIE experiment) is also presented. Least squares fits of the observed MOMRIE lines to the coupled theory provide accurate determinations of the fine and hyperfine structure parameters. Parameters determined in this way include those commonly referred to as the spin-orbit coupling constant, the spin-spin coupling constant, the dipolar hyperfine coupling constant, the orbital angular momentum hyperfine parameter, and the orbital angular momentum g factor. Vibrational variation of the fine structure parameters is easily measurable while that of the hyperfine structure parameters is comparable to the experimental error. The linewidth of the MOMRIE transitions yields a lifetime of 32±5 nsec for the state.
Electron affinities of Cu and Ag
Authors: Hotop H. , Bennett R. A. , Lineberger W. C.
Published: February 2004

In a crossed-beam experiment, photodetachment of Cu− and Ag− ions by an Ar-ion laser beam (4880 Å) is studied by energy analyzing the detached electrons. The electron affinities are found to be: E.A. (Cu)=(1.226 ± 0.010) eV, E.A. (Ag)=(1.303−0.011+0.007) eV. These electron affinities are approximately 0.5 eV less than those determined by surface ionization studies. The surface ionization technique is discussed and possible reasons for the discrepancies are advanced. The new electron affinities are used to estimate those of the atoms in the long series of the periodic table. Measurements of the angular distribution of the photodetached electrons yield β=2.00 ± 0.03 for the anisotropy parameter β in both cases.
Dye-laser photodetachment studies of Au−, Pt−, PtN−, and Ag−
Authors: Hotop H. , Lineberger W. C.
Published: February 2004

Photodetachment of Au−, Pt−, PtN−, and Ag− ions is studied in a crossed-beam experiment, in which a 2 keV negative ion beam is intersected by a pulsed tunable dye laser (Δ λ ≈ 1–2 Å). The threshold behavior of the photodetachment cross section σ for Au− and Pt− is found to agree with Wigner's Law σ ∝ k2L+1 (k: momentum of outgoing electron with orbital angular momentum L) over about 50 meV above threshold for this case, in which L=1. The electron affinity of Au is (2.3086 ± 0.0007)  eV, that of Pt (2.128 ± 0.002) eV, whereas the one for Ag is <1.78 eV and very probably ≲ 1.5 eV. The PtN− cross section exhibits sharp peaks due to single-photon processes; these features are ascribed either to autodetachment or predissociation of excited long-lived (τ ≳ 5 × 10−13 sec) PtN−* molecules; the present experiment measures the total cross section for the production of neutral atoms (or molecules) and therefore cannot distinguish the two possibilities. Further, saturation experiments are described in which the laser flux is so high as to saturate partially the photodetachment. This method is applied to the case of Pt−, for which the absolute cross section of an excited component Pt−* in the beam is measured and thereby its fractional population is determined.
Effects of vibrational relaxation on molecular electronic transitions
Authors: Nitzan Abraham , Jortner Joshua
Published: February 2004

In this paper we explore the implications of the coupling between nonradiative electronic relaxation and vibrational relaxation in excited electronic states of large molecules. The physical model involved a two electronic level molecular system interacting with a harmonic medium via linear coupling terms in the molecular nuclear coordinates. Two models were advanced for the molecule-medium coupling which involve single phonon decay and alternatively double phonon (or rather phonon-vibron) decay. The functional form of our final results is independent of the specific model adopted for the vibrational relaxation. The molecular Hamiltonian and the intramolecular coupling were recast in terms of second quantization formalism where the nonadiabatic coupling operator was modified by a Franck Condon shift operator. The coupling between electronic and vibrational relaxation processes was formulated in terms of a generalized interaction picture, where the intramolecular coupling was treated to second order while the vibrational relaxation was handled to ``infinite order'' by the Wigner Weisskopf approximation as applied to the equations of motion for the nuclear operators for the normal molecular modes. The nonradiative decay rate of an excited electronic state was expressed in terms of a generalized time correlation function. We were able to demonstrate that our general expressions reduce to the (time independent) decay rate of a single vibronic level in the limit of slow vibrational relaxation and to a modified expression for the (time independent) decay rate of the thermally averaged electronic manifold in the limit of fast vibrational relaxation. In the general case of coupled electronic-vibrational relaxation the decay probability is time dependent. In the low temperature limit the nonradiative decay rate can be expressed in terms of a superposition of exponential functions.
Surface states of anthracene and naphthalene
Authors: Stern Peter S. , Green Michael E.
Published: February 2004

A calculation of the surface states of anthracene and naphthalene has been carried out, using a direct crystal orbital approach similar to a method which has previously been used by others for calculations of bulk states. Surface bands have been calculated for naphthalene together with associated mobilities. No separated surface bands were found for anthracene, although some isolated surface states were found.
Precision neutron diffraction structure determination of protein and nucleic acid components. X. A comparison between the crystal and molecular structures of L-tyrosine and L-tyrosine hydrochloride
Authors: Frey Michel N. , Koetzle Thomas F. , Lehmann Mogens S. , Hamilton Walter C.
Published: February 2004

The amino acid L-tyrosine (C9H11NO3) and its salt L-tyrosine hydrochloride (C9H11NO3·HCl) crystallize respectively in the space groups P212121, a=6.913(3) Å, b=21.118(10) Å, c=5.832(3) Å, and P21, a=11.083(5) Å, b=9.041(4) Å, c=5.099(3) Å, β=91.82(3) Å. Both structures have been refined by neutron diffraction techniques, and all the hydrogen atoms have been located precisely. The tyrosine molecule occurs in the zwitterion form in pure L-tyrosine while both the amino group and the carboxyl group are protonated in the hydrochloride. In both crystalline compounds there is a three-dimensional network of hydrogen bonds. Statistical tests show no significant differences between the bond lengths and valence angles in the compounds except for those atoms involved in hydrogen bonds. The conformational angles of the main chain (C, Cα, N, O1, O2) and those of the side chain differ only slightly in the two compounds while the mutual orientations of the main chain and of the side chain differ completely; in L-tyrosine N is gauche with respect to Cγ of the phenyl group while in the hydrochloride N is nearly trans to Cγ. The barriers to rotation of the ammonium groups are estimated to be 8.3 kcal/mole in L-tyrosine and 5.0 kcal/mole in the more weakly hydrogen bonded hydrochloride. Detailed statistical tests for L-tyrosine show very good agreement between the heavy atom structural parameters obtained from our work and those found in previous x-ray diffraction studies [A. Mostad, H. M. Nissen, and C. Ro/mming, Tetrahedron Lett. 1971, 2131, and Acta Chem. Scand. (to be published); J. Donohue and R. Bogg (private communication)]. Such tests also show that the standard deviations are quite well estimated in both the neutron and one of the x-ray studies (Mostad et al.).
Sound velocity in colloidal SiO2 suspensions
Authors: Younger Peter R. , Zimmerman George O. , Chase C. E. , Drost-Hansen W.
Published: February 2004

The velocity of sound in three colloidal suspensions of silica was measured in the temperature range between 10 and 75°C. The measurements show that the temperature dependence of the velocity is affected by the presence of the silica, but agreement between the observed values and classical theory, which considers the colloidal suspension made up of elastic particles, is poor. This suggests that the temperature and concentration dependence of the total hydrated SiO2 particles is important.
van der Waals-Lifshitz forces between anisotropic ellipsoidal particles
Authors: Imura Hidefumi , Okano Koji
Published: February 2004

van der Walls-Lifshitz forces between an ellipsoidal particle and a dielectric wall as well as between two ellipsoidal particles suspended in a liquid are calculated on the basis of the theory of McLachlan. The materials constituting the ellipsoids may be anisotropic. It is assumed, however, that in each ellipsoid the principal axes of the tensor of dielectric permeability coincide with those of the ellipsoid. The obtained formulas include those for spheroids by Kihara and Honda as well as those for spheres by Dzyaloshinskii, Lifshitz and Pitaevskii as particular cases. The variations of the free energies of interaction with respect to the mutual orientations of the interacting bodies are discussed. The three-body forces among three ellipsoids as well as among two ellipsoids and a wall are also calculated.
Partial vibration energy transfer map for methyl fluoride: A laser fluorescence study
Authors: Weitz Eric , Flynn George W.
Published: February 2004

Infrared fluorescence has been observed from the 2ν3 overtone, the ν3+ν6 combination band and the ν1, ν2, ν4, ν5, and ν6 fundamentals of CH3F after pumping of the ν3, 0→ 1 transition by the P (20), 9.6 μ line of a Q-switched CO2 laser. All observed states exhibit a single exponential decay curve with a rate of 0.59 msec−1· torr−1. The fluorescence risetimes of the ν6, ν2 and ν5, ν1 and ν4, and 2ν3 states were also observed. The rate of rise of the ν1 and ν4 fluorescence and the 2ν3 fluorescence is faster than 7 μsec at 1 torr. The ν6 fluorescence risetime is pressure dependent with a rate constant of 106± 21 msec−1· torr−1. The pressure dependent rate of rise of the ν2 and ν5 fluorescence is 86± 17 msec−1· torr−1. Measurements of the steady state dependence of the ν2 and ν5 fluorescence intensity versus laser intensity were made. The temperature dependence of the Q-switch excited fluorescence intensity from the 2ν3 and ν1 and ν4 states was also studied. No evidence of excited state absorption was observed and both sets of measurements indicate collisional processes rather than excited state absorption play the major role in establishing an equilibrium among the excited vibrational states of CH3F. The ramifications of these results for energy transfer mechanisms, laser action, and laser induced chemical reactions in polyatomic molecules are discussed.
Classical dynamical investigations of reaction mechanism in three-body hydrogen-halogen systems
Authors: Porter R. N. , Sims L. B. , Thompson D. L. , Raff L. M.
Published: February 2004

A theoretical investigation of the reaction mechanisms in eight different three-body hydrogen-halogen reactions has been accomplished by means of Monte Carlo averages over classical trajectories computed on reasonable semiempirical potential-energy surfaces. Two of the surfaces employed contain a single adjustable parameter characteristic of a halogen core charge while six others result from unadjusted computations. The analysis shows that dynamic effects resulting from momentum transfer require the reactions M2+X=MX+M (M=H,D, or T; X=Br or I) to proceed through excited vibrational states of M2. Reaction of the ground vibrational state is dynamically forbidden in each case. Reaction rate coefficients, associated activation energies, pre-exponential factors, and kinetic isotope effects calculated from rotationally averaged reaction cross sections are in reasonable agreement with experiment. The computations further suggest an origin for the isotope effect that is significantly different from that derived from statistical mechanical theory. A comparison of the relative magnitudes of the experimental activation energy and vibrational level spacing can be used to qualitatively predict the importance of dynamic effects in homogeneous gas-phase reactions of diatomic species.
Vibrational optical activity
Authors: Schellman John A.
Published: February 2004

Formulas are developed for the rotatory strengths of vibrational transitions utilizing a fixed-charge model. The formulas are applied to three molecular systems. Though the rotatory strengths of vibrational transitions are several orders of magnitude smaller than those for electronic transitions, the anisotropy factor of some bands are predicted to be comparable to electronic transitions. The latter is the important experimental quantity.
Generalized oscillator strengths for the excitation of heavy atoms; 61S→ 61P1, 61S→ 71S, and 61S→ 71 P1 transitions in mercury
Authors: Skerbele Ausma , Lassettre Edwin N.
Published: February 2004

Generalized oscillator strengths have been determined at 300, 400, and 500 eV for the 61S0→ 61P1,61S0→ 71S0, and 61S0→ 71P1 transitions in mercury. The generalized oscillator strength curves for the 61S0→ 61P1 transition separate with kinetic energy in the vicinity of the first minimum indicating deviations from the Born approximation. A minimum is also observed in the generalized oscillator strength curves for the 61S0→ 71S0 transition. The Born approximation does not hold for this transition. The generalized oscillator strength for the 61S0→ 71P1 transition shows strong effects of configuration interaction at small ΔP.
Selective nuclear Overhauser effect experiments on coupled spin systems
Authors: Krishna N. Rama , Yang Ping P. , Gordon Sidney L.
Published: February 2004

A formalism describing selective nuclear Overhauser effect (NOE) experiments on coupled spin systems is developed for the study of relaxation processes. The formalism is completely general, and is developed in terms of the fractional intensity changes Gab,cd of various transitions ab γ relative to the irradiated line cd. The general properties of the Gab,cd are discussed. The symmetry properties of coupled spin systems can be investigated conveniently using group theoretical considerations by setting up a geometrical figure to correspond to the relaxation problem. This procedure was illustrated for weakly coupled three-spin systems, where the systematics of selective NOE experiments can be described in terms of the transformation properties of a cube. Analytical expressions for the Gab,cd were obtained for the intramolecular dipole-dipole and external random field relaxation mechanisms. These expressions provide a good approximate description even for strongly coupled systems. Relaxation analyses were performed on the ABX proton system vinyl bromide and the A2X proton system 1,1,2-trichloroethane. It was shown that the particular experiment where an outer line of the X multiplet is saturated is quite sensitive to the detailed relaxation mechanism. The remaining lines of the X multiplet directly reflect the fractional contribution of the intramolecular dipole-dipole mechanism. The results for vinyl bromide were interpreted in terms of anisotropic reorientation using an inertial model. It is suggested that the selective NOE technique can be useful when information regarding molecular conformations is required, and the conventional NOE experiments (where an entire multiplet is saturated) are difficult to perform.
Crystal structure and bond character study in 3,5-dichlorophenol
Authors: Sasikala D. , Murty C. R. K.
Published: February 2004

Zeeman effect studies of Cl35 nuclear quadrupole resonance have been carried out at room temperature in a single crystal of 3,5-dichlorophenol. It was confirmed that the crystal belongs to monoclinic symmetry. Two inequivalent field gradient systems were observed. The asymmetry parameter of the field gradient was found to be 0.09± 0.03. The minimum number of molecules in the unit cell and the orientation of the molecular planes with respect to the C axis of the crystal, which is also the growth axis, have been determined. The bond characters of the C–Cl bond have been calculated using the experimental asymmetry parameter.
Forces between parallel dielectric surfaces
Authors: Craig R. A.
Published: February 2004

The energy of a half-space-slab-half-space (ε2-ε1-ε2) system was considered by a technique which treats all of the electronic degrees of freedom on an equal footing. This is in contrast with earlier work which only considered surface plasmon excitations and their modification due to proximity of the surfaces. The results of the energy so determined were seen to reduce properly in the limiting cases of the separation between the surfaces going to zero or infinity which is also in contrast to the earlier theories. From the total energy the force between the half-spaces was derived, and it was found that although this varies at large distances as the inverse cube of the separation as was the case for earlier works, the coefficients and detailed behavior are different.
Spin S = 1 in six-coordinated iron(II): Low-temperature magnetism, Mössbauer effect, and electronic structure
Authors: König E. , Ritter G. , Kanellakopulos B.
Published: February 2004

Magnetic susceptibilities down to 1.0°K and 57Fe Mössbauer spectra between 298 and 4.2°K are reported on Fe(phen)2ox· 5H2 O(I), Fe(phen)2mal· 7H2 O(II), and Fe(phen)2F2 · 4H2 O(III) (phen = 1,10-phenanthroline, ox = oxalate, mal = malonate). Between 300 and ∼ 15°K, the effective magnetic moments are almost independent of temperature at μeff = 3.76, 3.87, and 5.20 μB; below 15°K the moments start to decrease and, at 1.0° K and 8.60 kG, they assume values of 2.65, 2.64, and 3.71 μB, for I, II, and III, serially. A slight field dependence due to saturation effects is encountered in the cryogenic range. The results are consistent with a spin-mixed 3A2(ξ2η2εζ) ground state characterized by a zero-field splitting of |D|= 2.0–3.0 cm−1 and g values significantly higher than 2.0. The large effective g is indicative of mixing with the higher 5T2 multiplet. From the Mössbauer spectra, the quadrupole splittings were obtained as ΔEQ = 0.24, 0.26, and 0.25 mm sec−1, the isomer shifts as δIS= +0.29, +0.30, and +0.30 mm sec−1, for I, II, and III, serially, and both are temperature independent. In reasonable agreement, the quadrupole splitting of a 3A2 state is calculated as zero. The discrepancy with iron(II) phthalocyanine is resolved in that, for a 3B2 ground state, ΔEQ is calculated as consistent with experiment (ΔEQ = 2.70 mm sec−1).
Sodium-23 quadrupolar coupling constant and relaxation rate in sodium cyanide
Authors: O'Reilly Donald E.
Published: February 2004

The quadrupole coupling constant and asymmetry parameter of Na23 in orthorhombic NaCN is interpreted to yield the molecular quadrupole moment of the cyanide ion [Q= (−1.0± 0.1)× 10−16 cm2]. This value of Q is equal to the experimental value for isoelectronic CO, but is somewhat smaller than the value computed in the Hartree-Fock approximation. The Na23 nuclear relaxation rate is computed for several models of reorientation for the cyanide ion. Lack of agreement between the computed relaxation times and the observed value strongly suggests that the reorientational motions of neighboring cyanide ions are correlated.
Theory of ion-polar molecule collisions. Comparison with experimental charge transfer reactions of rare gas ions to geometric isomers of difluorobenzene and dichloroethylene
Authors: Su Timothy , Bowers Michael T.
Published: February 2004

A classical theory for the ion-permanent dipole interaction is developed that takes into consideration the thermal rotational energy of the polar molecule. The theory is formulated in terms of an r-dependent average orientation angle θ̄ (r) between the dipole and the line of centers of collision. The technique allows quantitative determination of the capture cross section as a function of ion-polar molecule relative velocity. In addition, capture limit rate constants are readily calculated both at thermal energies and as a function of relative energy. Charge transfer rate constants from various rare gas ions to difluorobenzene and dichloroethylene isomers have been measured at thermal energies using ion cyclotron resonance spectroscopy. Rate constants are considerably larger than predicted by the capture theories for both polar and nonpolar isomers indicating long range electron jump is a prevalent mechanism for charge transfer in these systems. The average-dipole-orientation theory developed in this paper adequately accounts for the effects of the permanent dipole moment on the rate constant.
Theory of the simplest substitution reactions
Authors: Brodsky A. M. , Levich V. G.
Published: February 2004

The dynamic equations describing the elementary substitution reactions are deduced. The expressions obtained are analyzed in the heavy mass limit of reacting particles. The connection between the peculiarities of reaction cross section from one side and the bound states characteristics and the regularities of elastic scattering from another is considered. The expressions obtained are compared with experimental data for the simplest substitution reactions.
Relaxation processes in excited CO states. II. Elastic cross relaxation
Authors: Slanger T. G. , Black G.
Published: February 2004

Interactions between the adjacent d 3Δν=7, e 3Σν=4−, and A 1Πν =2 levels of CO have been studied. By making d 3Δν=7 the initially excited level, it has been shown that the interconversion d 3Δν=7 → e 3Σν=4− is collisionally induced. Rate coefficients were measured, and when expressed as transition probability per gas kinetic collisions, the results are essentially the same for Ar, H2, N2, and CO—1 collision in 90. The He reaction probability per collision is much lower. Over-all deactivation coefficients for d 3Δν=7 and e 3Σν=4− were also obtained. The data are consistent with a radiative lifetime for the e 3Σν=4− level of ∞3 μsec. When the A 1Π state is pumped by resonance fluorescence, then collisions between Ar and A 1Πν =2 produce d 3Δν=7 and e 3Σν=4−, a process for which the cross section appears to be higher than for Δ3 →3Σ− conversion.
Concentration fluctuations in chemically reacting fluids
Authors: Garisto Frank , Kapral Raymond
Published: February 2004

A microscopic study of the total concentration fluctuations of the dilute reacting species in a ternary mixture is presented. A Fokker-Planck description of the concentration fluctuations of the molecules in specified internal states is used and the necessary matrix elements are evaluated by a variational method. Expressions for the contribution of these fluctuations to the light scattering spectrum are presented along with expressions for the nonequilibrium corrections to the rate coefficient which depend on frequency and wavenumber. The general features of the results are illustrated by considering specific stochastic models of chemically reacting fluids.
Theory and Monte Carlo simulation of physical clusters in the imperfect vapor
Authors: Lee Jong K. , Barker J. A. , Abraham Farid F.
Published: February 2004

A formal physical cluster theory for an imperfect gas, valid for an arbitrary definition of a ``physical cluster,'' is described. The role of the definition of the physical cluster is stressed. For a particular definition of the physical cluster, which may be appropriate in nucleation theory, the Helmholtz free energy of 13-, 43-, 60-, 70-, 80-, 87-, and 100-atom argon clusters is calculated in the classical limit for temperatures ranging from absolute zero to 100°K using Monte Carlo techniques. It is found that a cluster's free energy is almost independent of its definition provided that the definition is reasonable and the temperature is sufficiently low. The results are compared with the predictions using the harmonic approximation.
Use of nonrelativistic wavefunctions for the prediction of properties of molecules containing atoms of high Z. PbO as a test case
Authors: Schwenzer Gretchen M. , Liskow Dean H. , Schaefer Henry F. , Bagus Paul S. , Liu Bowen , McLean A. D. , Yoshimine Megumu
Published: February 2004

Using a minimum basis set of Slater functions, nonrelativistic self-consistent-field calculations have been carried out for the lead monoxide molecule. The purpose of the calculations was to provide an indirect test of the importance of relativistic effects in molecules containing atoms with atomic number as high as 82. The predicted spectroscopic constants of PbO are in about as good agreement with experiment as were the results from comparable calculations on the obviously nonrelativistic molecule CO. The electronic structures of the two molecules are briefly compared in terms of Mulliken population analyses.
Microwave spectrum of nitrocyclopropane
Authors: Mochel Alan R. , Britt Chester O. , Boggs James E.
Published: February 2004

The microwave spectrum of nitrocyclopropane has been investigated in the 8–40-GHz region. Transitions in the ground state and five excited states of the torsional mode have been assigned. The ground state of a monodeuterated nitrocyclopropane has also been assigned. The conformation of the molecule is found to be the bisected one with the plane of the nitro group perpendicular to the plane of the cyclopropyl ring. The torsional frequency (70± 20 cm−1) of the nitro group and the barrier to internal rotation (1100± 500 cm−1) have been derived from relative intensity measurements of transitions in the ground and first torsional states. The dipole moment is found to be 3.95± 0.10 D.
Model calculations of transport coefficients for a gas of linear 1Σ molecules in a static electric field
Authors: Cooper E. R. , Hoffman D. K.
Published: February 2004

A brief analysis of the influence of a static electric field on the thermal conductivity and viscosity of linear 1Σ molecules (with and without a permanent dipole) is presented. Solutions are generated for trial functions including the infinite set of irreducible angular momentum tensors [Ω](l) for the viscosity and W[Ω](l) for the thermal conductivity. A rigid ellipsoid model is used to calculate the transport coefficients of N2 and CO for trial functions including angular momentum tensors of rank as high as 4.
On the electron binding energy in negative ions
Authors: Schmidt-Böcking H. , Bethge K.
Published: February 2004

A new method has been developed to determine the electron binding energy in negative ions from charge exchange cross sections, which are proportional to the sum of the inverse binding energies.
Relativistic and nonrelativistic magnetic-dipole hyperfine matrix elements for molecular calculations
Authors: Lipas P. O. , Pyykkö P. , Pajanne E.
Published: February 2004

The magnetic-dipole hyperfine matrix element is calculated from the Dirac theory for electronic wavefunctions centered at the origin and the nucleus arbitrarily located. The nonrelativistic limit of the result is constructed for any wavefunctions of the form RnlYlmlχms. It is a single expression, which is checked to equal the sum of the conventional orbital, spin-dipole, and contact terms. Also the matrix element of the A2 term is given for two arbitrarily located nuclei.
Entropy production for a near-equilibrium isolated system of thermalizing matter and radiation
Authors: Rueda A.
Published: February 2004

It is shown that for an isolated system near equilibrium involving the quenching of luminescence inside a perfectly reflecting cavity, successive time derivatives of the system entropy alternate in sign. The system consists of two-level atoms or molecules weakly coupled by absorption and emission to a radiation field in a narrow band and strongly coupled by nonradiative interactions to other atoms and molecules in the rest of the system. Everything is enclosed in a perfectly reflecting and thermally insulated cavity.
ESR Study of radicals formed in γ-irradiated single crystals of K2NbOF5 · H2O
Authors: Shock John R. , Rogers Max T.
Published: February 2004

A single-crystal ESR study has been made of K2NbOF5· H2O γ irradiated at 77°K. Two 93Nb-centered radicals were observed at 77°K; one of these is shown to be [NbOF5]3− with a d1 configuration and a dxy ground state and the g, A (93Nb), and A (19F) tensors for this radical have been evaluated. The A (19F) fluorine superhyperfine interaction tensor for the equatorial fluorine ligands indicates strong in-plane π bonding between the niobium 4dxy orbital and the 2py orbitals of fluorine. The g and A (93Nb) parameters have also been used to calculate molecular orbital coefficients for this complex. On warming, the [NbOF5]3− radical decays at −80°C leaving a second radical, the ESR spectra of which suggest that it is a hole species formed by the removal of an electron from [NbOF5]2−.
Studies of the two-electron cavity species in metal-ammonia solutions
Authors: Copeland David A. , Kestner Neil R.
Published: February 2004

A model which includes all factors determining the absolute stability of two electrons in one cavity in metal-ammonia solutions is solved. It predicts that such a species is unstable relative to two one-electron species by about 1 eV per electron. Other physical properties of this species also suggest it is not present. Alternative mechanisms must be responsible for spin pairing.
Fluorescence efficiencies of nitrogen and air excited by neon and sodium ions at 0.3–2.0 MeV
Authors: Langley Robert A.
Published: February 2004

The fluorescence efficiencies for excitation of nitrogen and air by neon and sodium ions have been measured at bombarding energies between 0.3 and 2.0 MeV. The molecular spectra studied were the first negative system of N2+ (1N) and the second positive system of N2 (2P). The atomic spectra studied were the N+ 5003 Å multiplet and the N+ 5680 Å multiplet. The fluorescence efficiencies of the 3914 Å band and the 4278 Å band of the 1N system and the 3371 Å band of the 2P system were derived directly from the fluorescence data as were the efficiencies of the 5003 Å and 5680 Å multiplets. Efficiencies relative to the 3914 Å band were estimated for the (ν′ = 0, ν″ = 0–3) bands of the 1N system and the (ν′ = 0, ν″ = 0–5), (ν′ = 1, ν″ = 0–6), and (ν′ = 2, ν″ = 2–7) bands of the 2P system. In addition, collisional deactivation coefficients for the 5003 A and 5680 A multiplets were derived from the efficiency data. The efficiencies of all spectra studied increased with increasing energy, with the efficiency of the 3914 Å band being the largest (0.48%) at 2.0 MeV for Ne+ in N2. The ratio of the intensity of the 4278 Å band to that of the 3914 Å band indicates that the Franck-Condon principle is obeyed in this particular case. Also, the ranges of neon and sodium in nitrogen and air were obtained from emission measurements.