bluuebunny/crossref_metadata_2025 huggingface dataset:
Gaseous Diffusion in Neon-Noble-Gas Systems
Authors: Malinauskas A. P. , Silverman M. D.
Published: February 2004

Diffusion coefficients of all four neon–noble-gas binary systems are reported as determined with a two-bulb apparatus over the temperature range o°-120°C. The experimental values, reduced to 1 atm pressure and trace composition of the heavier component, can be described by the expressions He–Ne, log10D12 = 1.631 log10T − 4.0051; Ne–Ar, log10D12 = 1.672 log10T − 4.6357; Ne–Kr, log10D12 = 1.757 log10T − 4.9332; Ne–Xe, log10D12 = 1.690 log10T − 4.8308. The present data are in favorable accord with the results of other workers and with diffusion coefficient values that are derived from studies of the composition dependence of the viscosity coefficient. Values derived from the composition dependence of the thermal conductivity coefficient are in fair agreement in general, but this method does not provide nearly as reliable a means of obtaining diffusion coefficient data as does viscosity.
Triplet-State Zero-Field Splittings in Some Aromatic Hydrocarbons and Nitrogen Heterocycles
Authors: Gondo Yasuhiko , Maki August H.
Published: February 2004

The SCF-AO's expanded by Löwdin have been used for the calculation of the electron spin dipolar interactions in the triplet-state zero-field splittings of some aromatic molecules. Within a framework of two-center approximation for the spin–spin interaction integrals over atomic orbitals, and adopting the Sklar-type approximation for the exchange-type integrals, excellent agreement with experiments has been obtained for benzene and naphthalene without invoking σ–π interactions. The wavefunctions used were obtained by means of the Pariser–Parr–Pople method, within a full single excitation configuration treatment. This approach has been extended to some aromatic nitrogen heterocycles, but the results, although promising, are poorer, possibly due to the neglect of spin–orbit coupling. Uncertainty in the choice of the C–N resonance integral and the neglect of penetration integrals in the core Hamiltonian may also be factors. Eleven molecules have been treated in all. For comparison, the single-determinant unrestricted Hartree–Fock wavefunctions also have been employed, but these give extremely poor agreement with experiment.
Macroscopic Quantum Electrodynamics
Authors: Fulton Robert L.
Published: February 2004

The quantities which relate the propagation of the electromagnetic field variables to experimentally measurable quantities are the expectation values of products of the field operators, 〈a(1)〉, 〈a(1)a(2)〉, etc., where a(1) denotes the vector potential at space–time point 1. These expectation values can be evaluated from a suitably defined generating functional. The set of equations which determines this functional in the presence of matter is particularized to the case in which matter exhibits a linear response to the transverse components of the radiation field. An explicit form is found for the generating functional, and in this linear realm, the close similarity of the propagation of the quantum fields to that determined by the classical phenomenological equations is pointed out. In the case in which matter exhibits a nonlinear response to the radiation field, the equations which determine the generating functional are reduced to an equation of motion for the expectation value of the vector potential. The result is a generalization of the classical nonlinear phenomenological Maxwell equation to include quantal effects. An alternative approach to the inclusion of higher-order effects is by the introduction of a formally exact form for the generating functional. From this exact form, a systematic perturbation expansion which uses the generating functional found in the linear case as the zeroth-order solution is given. The perturbation procedure gives a method for the direct calculation of higher-order corrections to the expectation values of products of the field operators. The technique is illustrated by deriving the first nonlinear corrections to 〈a(1)〉 and 〈a(1)a(2)〉. These corrections correctly include the quantal aspects of the radiation field and represent generalizations of the corresponding classical results. The expression found for 〈a(1)a(2)〉 gives a theoretical description of Raman and Rayleigh scattering of radiation by matter in bulk, including nonlocal time and space effects. In order to deal with problems associated with the breakdown of the above approximations in the case of strong fields, a procedure is given by which either classical fields or operator fields can be introduced so as to mimic the effects of the strong fields in the zeroth approximation. In this latter situation an effective susceptibility which determines the propagation of the radiation field is found in the case of linear response to incident radiation.
Scattering of K and Cs by Several Compounds
Authors: Greene E. F. , Hoffman L. F. , Lee M. W. , Ross J. , Young C. E.
Published: February 2004

The nonreactive scattering of K from C10H16, (CH3)3CBr, SiCl4, Cl2, Br2, I2, ICl, (CN)2 C=C(CN)2, and Cs from HBr has been studied in experiments with crossed molecular beams. The primary alkali metal beam was velocity selected, and the scattered alkali metal was measured as a function of laboratory angle at a number of initial relative kinetic energies. Potential parameters are calculated from the rainbow scattering for K+C10H16, (CH3)3CBr, SiCl4, and Cs+HBr and also from the supernumerary rainbows for K+C10H16 and CH3)3CBr. An optical model analysis on K+(CH3)3CBr and Cs+HBr yields information about threshold conditions for reaction, probability of reaction, and total reaction cross section as a function of relative energy. For systems without rainbow scattering [K+halogens, (CN)2C=C(CN)2] an optical analysis made with a simple form for the absorption function requires a gradual change from a van der Waals potential at very large distances of separation of reactants to a more attractive potential at smaller distances. This indicates a gradual electron transfer on approach of reactants rather than an abrupt electron jump.
NMR Study of Molecular Motions and Phase Transitions in Cyclohexene
Authors: Saffar Z. M. El , Eades R. G. , Llewellyn J. P.
Published: February 2004

NMR measurements of the mean-square width and the spin–lattice relaxation time have been made in polycrystalline cyclohexane from 65°K to the melting point 169.7°K. The results show that cyclohexane has three solid phases and two forms of molecular reorientations. On cooling the specimen, phase III (169.7°–128.5°K) is obtained first, followed by phase I (128.5°–65°K). On warming the specimen to 110°K an irreversible transition from phase I to phase II takes place. Another irreversible transition from phase II to phase III takes place at 138.8°K. In phase I, the lattice is essentially rigid below about 100°K, while above this temperature, classical rotation about an axis normal to the “plane” of the molecule takes place. Above 115°K ring inversion of the half-chair form of the molecule is believed to take place, and in phase III this motion becomes effective in reducing the mean-square width. Phase II, which persists below 138.8°K, is characterized by the absence of molecular motion.
Core Model for Single-Center Calculations of Electric Field Gradients. Application to LiD
Authors: Avgeropoulos George N. , Ebbing Darrell D.
Published: February 2004

The nuclear quadrupole coupling constant provides an example of a property which is sensitive to the form of the electronic wavefunction in the region of the quadrupolar nucleus. A method is discussed in which the wavefunction is separated into a core and a portion surrounding the quadrupolar nucleus. This latter portion of the wavefunction is determined by means of a single-center expansion. Calculations of the electric field gradient at the deuteron in LiD are presented. The dependence of the calculations on the core and on the position of the expansion center is studied. The results are in good agreement with experiment and more elaborate calculations.
Infrared Spectrum of Matrix-Isolated (NO)2
Authors: Guillory William A. , Hunter Charles E.
Published: February 2004

Matrix-isolated (NO)2 has been obtained by rapid deposition of NO–N2 mixtures on an optical window at 15°K, by limited diffusion of matrix-isolated NO at low temperatures, and by photochemical production of O atoms in an N2O environment. Controlled low-temperature studies allowing limited molecular diffusion indicate spectral growth patterns due to three different species. Experiments carried out with 15NO and N18O isotopic samples along with the photochemical production of (NO)2 suggests that cis and trans O=N=N=O and possibly another unstable cis form are produced.
Flash Decomposition of Acetylene, Ethylene, Ethane, and Methane on Tungsten
Authors: Rye Robert R. , Hansen Robert S.
Published: February 2004

The decomposition of acetylene, ethylene, ethane, and methane initially adsorbed on tungsten wires at 95°K was investigated by flash-filament spectroscopy, with products identified by mass spectroscopy; the major gas-phase product was hydrogen in all four cases. The flash-filament spectrum of ethylene consists of two equal hydrogen peaks resulting from a two-step dehydrogenation of chemisorbed ethylene: *CH2–CH2*→ lim >200°K*CH=CH*+2H*, CH*=CH*→ lim >̃300°K(C2)+2H*, 2H*→ lim fastH2(g). Acetylene dehydrogenation follows Reactions (2) and (3). When compared to previous results obtained on iridium, ethylene is seen to be more unstable on tungsten than on iridium. [Reaction (1) proceeds at an appreciable rate above 200°K on tungsten but only above 400°K on iridium.] This difference in stability of surface ethylene is discussed in terms of the possible surface structures of ethylene imposed by the topography of the metal surface. Adsorption of ethane and methane at 95°K is interpreted in terms of the following steps:CH4(g)→*CH3+H*, C2H6(g)→*CH2–CH3+H*, and, where adjacent sites are available, *CH2–CH3→*CH2–CH2*+H*. Detailis found in the flash-filament spectra resulting from each of these surface species. The major peak in the spectra of both ethane and methane occurs at 570°K and is attributed to the decomposition of the surface methyl group (*CH3) in the case of methane, and the surface ethyl group (*CH2–CH3) in the case of ethane. A mechanism is proposed for the decomposition of these species which is consistent with the present results and with the hydrogenolysis activity of tungsten.
Approximate Analytical Solutions of the Thomas–Fermi and Thomas–Fermi–Dirac Equations and Calculation of Diamagnetic Susceptibilities
Authors: Csavinszky P.
Published: February 2004

Recently derived approximate analytical solutions of the Thomas–Fermi (TF) and Thomas–Fermi–Dirac (TFD) equations, together with the latter's analytical extension involving the correlation effect, are used for calculating the diamagnetic susceptibilities of Ar, Kr, and Xe. It is concluded that the agreement of the calculated susceptibilities with experimental data, especially in the case of the TFD model, is comparable in accuracy with quantum-mechanical calculations.
Measurement of the Molecular g Values in H2O and D2O and Hyperfine Structure in H2O
Authors: Kukolich Stephen G.
Published: February 2004

Individual components of the Zeeman transitions in the rotational spectrum of H2O and D2O were resolved in fields of 25–30 kG. This allowed determination of the g values with greater accuracy than previous measurements. The g values obtained for H2O were g(523) = 0.6959 ± 0.001 and g(616) = 0.6565 ± 0.001. The g values obtained for D2O were gaa = 0.3233 ± 0.001, gbb = 0.3580 ± 0.001, and gcc = 0.3226 ± 0.001. Analysis of the combined results indicates that the g values for H2O are positive and that the values are gaa = 0.6650 ± 0.002, gbb = 0.7145 ± 0.002, and gcc = 0.6465 ± 0.002. Hyperfine structure on the 616 − 523 transition in H2O was observed in a maser spectrometer, and the spin–rotation and spin–spin coupling constants were obtained. The measured value of the rotational transition frequency was 22 235 079.85 ± 0.05 kHz. The magnetic susceptibility anisotropies and molecular quadrupole moments were determined in H2O.
Decay of Correlations in Linear Systems
Authors: Fisher Michael E. , Wiodm B.
Published: February 2004

The conditions under which the decay of the pair correlation function at large distances is monotonic or oscillatory are investigated for one-dimensional systems and discussed in detail for certain linear continuum and lattice models in which the molecules interact only with their nearest neighbors. In each case a locus is found in the pressure–temperature plane and in the density–temperature plane, such that in thermodynamic states of the one-dimensional fluid that lie on one side of the locus, the decay of the correlation function is oscillatory, and in those that lie on the other side it is monotonic. At every temperature the decay is monotonic below a uniquely determined transition pressure or density. It is argued that such loci will likewise be found in real three-dimensional systems, and that the critical point and a range of fluid states around the critical point, as well as states of the low-pressure vapor, will lie in the region in which the correlation function at large distances is asymptotically positive and decays monotonically.
Dipole Moments of the Lowest Singlet π* ← π States in Phenol and Aniline by the Optical Stark Effect
Authors: Lombardi John R.
Published: February 2004

The Stark effect in the rotational fine structure is used to measure the change in dipole moment on excitation in aniline and phenol. The spectra are in the 0–0 bands of the lowest-lying singlet π* ← π states. The results are | Δμ | = 0.85 ± 0.15 D for aniline and | Δμ | = 0.20 ± 0.20 D for phenol. Evidence is presented which indicates that the sign of Δμ is positive. If this is true, these results correlate well with the structural changes on excitation, namely, that the contraction along the in-plane long axis is considerably greater in aniline than phenol. This correlation is strong indication of the extent of contribution of quinoidlike resonance structures to the electronic nature of the excited state.
Molecular Motion in ortho-Terphenyl
Authors: McCall D. W. , Douglass D. C. , Falcone D. R.
Published: February 2004

Nuclear magnetic relaxation measurements have been made for ortho-terphenyl in the liquid, crystalline, and glassy form. Self-diffusion coefficients have been measured in the liquid. Molecular correlation frequencies derived from these measurements are shown to correlate well with published viscosity data. The results were found to be described satisfactorily by an equation of the form νc = A″ exp[−B′ / (T−Tg)], but not by an equation of the form νc = A exp(− C / TSc), where Sc is the configurational entropy. Comments are made on the derivation of these functions and the nature of the molecular motions.
Rubber Elasticity
Authors: Imai Satoshi , Gordon Manfred
Published: February 2004

Rubber elasticity is treated in terms of a general random network bead-spring model which expresses chain connectivity through Dirac delta functions. In contrast to the classical theory, the present starting point is the segmental distribution function, from which, besides elasticity, most polymer properties are deducible, e.g., relaxation spectra, intrinsic viscosities, etc. The method is that developed by Fixman and by Imai. The salient results are: (a) macroscopic observables correspond to mean-square vector quantities; (b) rubber elasticity is a function only of the strain invarient I1 (not of I2); in particular: (c) the C2 term of the Mooney–Rivlin equation reflects effects of network connectivity (e.g., the functionality of cross links), not of I2; (d) The new one-parameter stress–strain equation here derived fits classical data on one- and two-dimensional strain. The quantity corresponding to the “front factor” in the classical equation is ∼ 1.8, in reasonable agreement with measurements by Ferry et al.
Oscillator Strengths and Rotational Strengths in Hartree–Fock Theory
Authors: Harris Robert A.
Published: February 2004

The various expressions for oscillator strengths and rotational strengths are examined within the context of Hartree–Fock theory. They are shown to be inequivalent. The f-sum rule, rotational sum rule, and the origin dependence of rotational strengths are also examined. It is shown that the time-dependent Hartree–Fock theory removes the difficulties.
Further Considerations on the Surface Free Energy of Embryonic Droplets in the Nucleation of a Liquid from the Vapor
Authors: Abraham Farid F.
Published: February 2004

Recent attempts to resolve the disagreement between the present theories of vapor condensation and experiment has centered around suggesting models for the surface structure of embryonic droplets which differ from the flat-plane surface structure for the case of hydrogen-bonded liquids. In this paper we extend these studies. First, a brief review of the bulk and interface structure of liquid water is presented. We then extend the discussion to other liquids studied in nucleation experiments and learn that certain fundamental features of their bulk surface structure enables us to categorize them in two distinct classes: (a) liquids which exhibit orientation of the polar molecules at the liquid interface and (b) liquids of quasispherical molecules which exhibit no ordering at the interface. Also, liquids of class (a) follow the Becker–Döring nucleation theory, and liquids of class (b) follow the Lothe–Pound nucleation theory. Possible surface structure models for embryonic droplets are discussed. We conclude that the failure of the Lothe–Pound theory to explain the nucleation of polar liquids is due to its failure to account for the deviation of critical nucleus surface properties from bulk liquid surface properties. The apparent success of the Becker–Döring theory to predict the nucleation of polar liquids is believed to be fortuitous.
High-Frequency Effects in the Spin Relaxation of Diatomic Gases
Authors: Chen F. M. , Snider R. F.
Published: February 2004

The high-frequency effects on NMR relaxation times due to the coherence between different rotational j states is considered. It is shown how steps in the T1/ρ-vs-ρ curve can arise as a result of this mechanism. A generalized Boltzmann equation valid for density matrices nondiagonal in j states is required for this treatment, and this equation is briefly presented.
Optical Absorption in Tetracyanoquinodimethan
Authors: Mookherji T. , Arnett G. M.
Published: February 2004

Reflection and transmission measurements in the range 0.29–2.5 μ are made on “as grown” surfaces of tetracyanoquinodimethan. The data are analyzed by Kramers–Kronig method to yield the optical constants. Optical constants were also calculated from the reflectance measurements at different angles of incidences using Fresnel's equations. The absorption coefficients thus obtained are interpreted in terms of an allowed direct transition which was further verified by transmission measurements.
Improved Perturbation Theory for Inelastic Encounters
Authors: Roberts R. E.
Published: February 2004

An improved perturbation theory for inelastic bimolecular collisions is proposed, which is based upon the suitable choice of an effective distortion potential derived from a second-order adiabatic optical potential. Since the new theory involves simply a rescaling of the original effective interaction, essentially no additional labor is required to obtain the corrected transition probabilities, at least for the special case of a one-dimensional problem. For example, an application to the prototype problem of vibrational relaxation, namely the collinear collision of an atom with a harmonic oscillator, reduces the error of the usual distorted wave approximation from 116% to 5%, averaging over all cases for which exact multistate results exist for comparison. Furthermore, a simple prediction concerning the accuracy of the distorted wave approximation for resonance transitions is borne out by exact results.
Proton Spin Relaxation in the Liquid Crystal PAA
Authors: Dong Ronald Y. , Forbes W. F. , Pintar M. M.
Published: February 2004

The proton spin–lattice relaxation time of the liquid crystal para-azoxyanisole (PAA) was studied at 30 MHz in the temperature range 125–445°K. The rotating frame experiment was performed at 15 and 30 MHz in a rotating field of 6 G over the temperature interval 125–425°K, and the rotating field strength dependence of T1ρ was studied in the range 1.6–16 G at three different temperatures. These observations show that in the nematic phase three processes are contributing to the spin–lattice relaxation: a slow cooperative mode, ωs ∼ 10 sec−1, the translational diffusion, and the order parameter fluctuation as proposed by Pincus. In the isotropic phase the order parameter fluctuations contribute much less because of the small size of the order clusters. The frequency and temperature dependence of various mechanisms are discussed and it is shown that the time autocorrelation function of the collective order fluctuations decays nonexponentially in the nematic phase.
CNDO Calculation of the Pseudorotational Potential Energy of Fluorocyclopentane
Authors: Carreira L. A.
Published: February 2004

The potential energy for pseudorotation in fluorocyclopentane, C5H9F, has been calculated using the CNDO/2 approximate quantum-mechanical method of Pople, Santry, and Segal. Calibration of the method for cyclopentane itself predicts an energy difference between the twisted and bent forms of less than 4 cm−1, in good agreement with experiment. For fluorocyclopentane energies calculated at different values of the phase angle φ are fit by a cosine-barrier potential. Only the bent equatorial form is calculated to be stable, with a calculated barrier to pseudorotation of 356 cm−1. Frequencies of permitted transitions are calculated and found to be in good agreement with experiment.
Molecular Beam Electric Resonance Spectrum of 31P14N
Authors: Raymonda John , Klemperer William
Published: February 2004

The radio frequency spectrum of PN is reported. The hyperfine structure constants of the first three vibrational states are fitted by μυ = 2.7511 − 0.0086 (υ + 12) ± 0.0006 D, (eqQ)N = − 5172.8 + 60.7 (υ + 12) ± 0.5 kHz, CP = − 78.2 ± 0.5 kHz, CN = 10.4 ± 0.5 kHz.
Atomic Form Factor for Neutral Carbon
Authors: Brown Robert T.
Published: February 2004

The atomic form factor for neutral carbon has been calculated with a Hartree–Fock wavefunction and with three configuration-interaction wavefunctions of varying accuracy. Values obtained with the variational wavefunctions differ from Hartree–Slater values by several percent for all values of the momentum transfer. For all but quite small values of the momentum transfer the difference between variational and Hartree–Fock values lies between 0.10% and 0.15%.
Statistical Theory of Bimolecular Exchange Reactions: Angular Distribution
Authors: White R. A. , Light J. C.
Published: February 2004

The statistical theory of chemical reactions is extended to describe the angular distributions of the products. The random phase approximation is used and the coefficients of the spherical harmonics are computed statistically. The distributions, symmetric about 90° in the center-of-mass frame, are then transformed to the lab frame. Application was made to the Rb+CsCl→RbCl+Cs reaction. The agreement with experiment is only moderate, implying that the statistical theory predicts too little internal excitation of the products in spite of the fact that experimentally the formation of a complex seems likely.
Thermal Diffusion Columns and Intermolecular Potential. III. The Noble Gases Ar and Xe
Authors: Yarza J. C. , Hidalgo M. A. , Alvarez D. González , Savirón J. M.
Published: February 2004

A hot-wire thermal-diffusion column is used to study steady-state separation. The relation ln Q̄0*exptl = m̄ ln Q̄0*theoret, which was extablished for Kr in earlier works in this series, is now extended to Ar and Xe in this type of column, and m̄ is shown to be a temperature independent constant in the range of our measurements. FJO theory gives a very good prediction for the optimum pressure measured experimentally in well constructed and operated columns for all temperatures of the wire (400–1100°K). Different molecular interaction parameters chosen for the theoretical calculation of p*theoret, when these are all reasonably realistic, give very similar results for p*theoret. The differences are similar to those obtained when interpreting, with the same parameters, the viscosity coefficients of the gas in the mean temperature range of the column. From these methods of comparison some conclusions can be drawn about constructional facts.
Diffuse Orbitals in Lower States of the Oxygen Molecule
Authors: Morokuma Keiji , Konishi Hideyuki
Published: February 2004

An ab initio SCF CI calculation was carried out for several lower states of O2 with various basis sets including diffuse pπ orbitals. Extensive CI calculations with basis sets including diffuse 2s and 2pπ functions show that the B 3Σu− state is essentially a valencelike state as well as the c 1Σu−, C 3Δu, and A 3Σu+ states, e.g., in the X 3Σg− state 〈z2〉 = 7.51 and in the B 3Σu− state 〈z2〉 = 8.84 a.u. Various levels of calculations are compared with existing theoretical results. The oscillator strength of the B 3Σu− ← X 3Σg− transition is calculated to be 0.167 in agreement with the experiment. A qualitative discussion of the molecular dimension of the B state is also made.
On the Relation between Unimolecular Reaction and Predissociation
Authors: Rice O. K.
Published: February 2004

Attention is again directed to the analogy between unimolecular decomposition and predissociation. In the reverse of unimolecular decomposition two fragments recombine, and in the usual equilibrium theory it is assumed that the reaction coordinate passes freely over a potential-energy hill (actually saddle point), regardless of energy. The analogous situation in predissociation must be sought by considering the equilibrium rate of transfer from a continuum state of fixed energy to a discrete state or states. For a model calculation there is first considered the case of a single continuum and an infinite number of uniformly spaced discrete states, with a uniform interaction matrix component, υsd, between the continuous and the discrete states. The perturbed stationary states have been found in terms of the unperturbed states of the discrete set, with spacing ΔEd between energy levels, and the continuum, which has itself been converted into a close-spaced set of discrete states with spacing Δεs. This gives some very interesting relations between the perturbed and unperturbed energy levels. The results depend on a dimensionless invariant parameter f = π2υsd2 / ΔεsΔEd. It is found that f = 1 gives results analogous to the transition state theory of unimolecular reactions, with flux from the continuum being absorbed in the discrete states completely and uniformly at any energy. With any other value of f, part of the flux is reflected, except at the center of the discrete line. The theory is extended to the case of many continua, and it is shown that the usual unimolecular rate theory can be described roughly as corresponding to a situation in which the discrete levels are divided into subsets, each subset connecting with a pair of continua, being independent of the other subsets, and having the average value of f equal to 12 rather than 1. Similar considerations apply to isomerizations.
Diffusivity of 3He, 4He, H2, D2, Ne, CH4, Ar, Kr, and CF4 in (C4F9)3N
Authors: Powell R. J. , Hildebrand J. H.
Published: February 2004

An earlier paper from this laboratory reported that diffusion coefficients of gases in CCl4 multiplied by their molecular cross sections are the same for gases heavier than Ne, but that they increase linearly from D2 to 4He with the square of the de Boer quantum parameter A*. The present study of gases in (C4F9)3N includes 3He. For relative cross sections we use, instead of uncertain values of σ2, the 23 power of the critical volumes, Vc, accurately known from critical densities. Measured values conform to the equation 102DVc2/3 = 70(1+1.94Λ*2). Diffusion coefficients in CCl4, multiplied by Vc2/3 yield 102DVc2/3 = 70(1+3.00Λ*2). The relative steepness of the two quantum lines is 3.00 ÷ 1.94 = 1.60, exactly the same as the ratio of the internal pressures of the two liquids, 3350/2160.
Water Cluster Formation Rates of NO+ in He, Ar, N2, and O2 at 296°K
Authors: Howard Carleton J. , Rundle Howard W. , Kaufman Frederick
Published: February 2004

Reaction rates of NO+ and its hydrates, NO+· n H2O(n=1–3), with water were measured in a flow system. The mechanism for conversion of NO+ hydrates to H3O+ hydrates was confirmed, and rate constants for the sequence of six clustering, redissociation, and rearrangement reactions were determined for each of the four carrier gases He, Ar, N2, and O2.
Non-Steady-State, Hot Wire, Thermal Conductivity Apparatus
Authors: Davis Phil S. , Theeuwes Felix , Bearman Richard J. , Gordon Roger P.
Published: February 2004

A non-steady-state, hot wire apparatus has been constructed to measure the absolute or relative thermal conductivities of fluids. With the use of a four-lead bare wire probe, a precision of 0.1%, and an absolute accuracy of ± 1% have been obtained. A quartz-coated film sensor is used to obtain relative thermal conductivity data for salt water solutions with a precision of 1% and an over-all accuracy of ± 2%. A comparison is made with experimental data available from the literature. For toluene, a comparison is made with the extrapolated values of Poltz and Jugel from which errors due to radiation have been eliminated for the parallel plate apparatus. The values agree within experimental error.
Phosphorescence of Benzophenone, Benzophenone-d10, and Decafluorobenzophenone in Rigid Glasses and Crystals under Pressure
Authors: Simpson Jerry , Offen Henry
Published: February 2004

The phosphorescence of benzophenone, benzophenone-d10, and decafluorobenzophenone has been studied as a function of pressure (0–30 kbar) at 77°K in nonpolar and polar glasses, as well as from molecules at pressure-induced defect sites in the corresponding crystals. The pressure shift in the triplet spectra is in the order Δ ν F > Δ ν D ≳ Δ νH, while lifetimes are shortened 15%−25% at 30 kbar. The blue shift in hydroxylic glasses and the red shift observed both in hydrocarbon glasses and at crystal defects are rationalized in terms of hydrogen bonding, dielectric interactions, and repulsive interactions, respectively.
Molecular Beam Kinetics: Reactions of K and Cs with Alkyl Dihalides
Authors: Entemann E. A.
Published: February 2004

Crossed beam studies have been made of the reactions of K and Cs atoms with CH2I2, CH2Br2, CH3CHBr2, (CH3)2CBr2, and CH2Cl2. The CH2I2 reactions show properties similar to reactions of diatomic alkali molecules: the reaction cross sections are very large (≳150 Å2); the angular distribution of the alkali halide product peaks forward (in the center-of-mass system) with respect to the incident alkali beam; and the most probable translational energy of the products is a small fraction (≲10%) of the available energy (∼ 35 kcal/mole). The RBr2 systems show more distinctive behavior: the reaction cross sections are two or three times larger for Cs than for K (∼ 50 Å2) but do not vary much with size of the alkyl group; the product angular distributions peak sideways, favoring the forward hemisphere for Cs, the backward hemisphere for K; and the product translational energy is a major fraction (roughly estimated as ∼ 50%) of the available energy (∼ 30 kcal/mole) for both the Cs and K reaction. For CH2Cl2 the reaction cross sections are below the detection limit (≲5 Å2). The variations in dynamical properties among these and other reactions are discussed in terms of the electron-jump model.
Molecular Beam Kinetics: Reactions of K and Cs Atoms with Unsaturated Halogenated Hydrocarbons
Authors: Entemann E. A. , Kwei G. H.
Published: February 2004

Crossed-beam studies have been made of the reactions of K and Cs atoms with C6H5I, CH2=CHCH2I, CH2=CHI,  CH2=CHCH2Br, CH2=CHBr, and CH2=CHCH2Cl. For these systems it was found that: (1) C6H5I, CH2=CHCH2I, CH3I (included for comparison), and CH2=CHCH2Br all gave comparable reaction cross sections ranging from ∼ 20–30 Å2 with K and ∼ 70–120 Å2 with Cs. CH2=CHI was much less reactive (≲5 Å2) and the remaining systems showed no measurable reaction. These results are compared with rate constants obtained from the early Polanyi sodium flame experiments. (2) The more reactive unsaturated halides produced nearly isotropic cesium halide product distributions in the c.m. system, whereas the corresponding potassium halide distributions peaked somewhat more strongly in the backward direction, although not as strongly as for CH3I. (3) Rough estimates of the final relative kinetic energy E′ of the products obtained from matching redundant branches in the LAB→c.m. transformations indicate that a substantial portion of the chemical energy released appears as internal excitation of the products. (4) There is some evidence for the formation of a long-lived collision complex in the reactions of C6H5I; the form of the product angular distribution indicates the complex is an oblate rotor in the critical configuration.
Dissociative Photoionization of H2O
Authors: Cairns R. B. , Harrison H. , Schoen R. I.
Published: February 2004

The photoionization of water vapor has been studied in the region 1000–200 Å. Cross sections for the production of H2O+, OH+, and H+ are reported together with information on the initial kinetic energies of these ions.
Stark Effect of NaLi X 1Σ+
Authors: Dagdigian P. J. , Graff J. , Wharton L.
Published: February 2004

The polarizabilities of the (J=1, M=0) and the (J=2, M=0) rotational states of the gaseous NaLi molecule have been measured by observing the refocusing voltages of a supersonic molecular beam with an electric quadrupole state selector. From these measurements the molecular electric dipole moment μ = 0.47 ± 0.03 D and the molecular electric polarizability were determined. The dipole moment is a factor of 2 smaller than predicted by two recent extended Hartree—Fock calculations (optimized valence configuration and configuration interaction), indicating a need for a more exact description of the bonding. The molecular polarizability is approximately equal to the sum of the atomic polarizabilities.
Electric-Field-Induced Spectra of Hydrogen Cyanide
Authors: Willson P. L. , Edwards T. H.
Published: February 2004

Electric-field-induced spectra (efs) of several absorption bands of HCN were experimentally produced and shown to exhibit the following phenomena: each of the three limiting case efs line shapes predicted by N. J. Bridge, D. A. Haner, and D. A. Dows [J. Chem. Phys. 48, 4196 (1968)], viz., normal, first derivative, and second derivative; two distinct types of induced transitions which are forbidden in the zero-field case; and l-type doubling enhancement of electric field effects. Although experimental conditions were such as to render the validity of a weak field approximation doubtful, line shapes as well as transition frequencies were found to agree with predictions based upon that assumption.
Theoretical Description of Molecular Rydberg States: B Σ+1 and Lowest Σ+3 States of BH
Authors: Pearson Peter K. , Bender Charles F. , Schaefer Henry F.
Published: February 2004

Ab initio calculations, including electron correlation, have been carried out on the X 1Σ+, B 1Σ+, and lowest Σ+3 states of BH. The last two states can be thought of as arising from the 1σ22σ23σ 4σ electron configuration. A double-zeta-plus-polarization and Rydberg function basis of Slater functions is used and electron correlation is considered through the use of approximate ``first-order'' wavefunctions. Optimum wavefunctions for the B 1Σ+ state are obtained by repeated diagonalization of the density matrix arising from the second eigenvalue of the Σ+1 secular equation. For the ground state the ab initio dissociation energy is 3.27 eV, compared to Gaydon's experimental value 3.54 ± 0.04 eV. Other spectroscopic constants for the X 1Σ+ and B 1Σ+ states are also in good agreement with experiment. The X—B separation is calculated to be 51 770 cm−1, compared to the experimental value 52 347 cm−1. The B 1Σ+ calculations confirm the double minimum predicted by Browne and Greenawalt. The lowest Σ+3 state is predicted by the present treatment to be Rydberg-like (with a minimum at 1.173 Å) for short internuclear separations and valencelike (repulsive) for large separations. A maximum occurs in the Σ+3 potential curve at 1.45 Å. Natural-orbital analyses and electron density plots are used to describe the valence to Rydberg ``transition.''
Single-Configuration Wavefunctions and Potential Curves for Low-Lying States of He2+, Ne2+, Ar2+, F2−, Cl2− and the Ground State of Cl2
Authors: Gilbert T. L. , Wahl Arnold C.
Published: February 2004

Wavefunctions, orbital energies, and potential curves for He2+, Ne2+, Ar2+, F2−, and Cl2− have been calculated in the molecular-orbital, self-consistent-field approximation over a range Re ≲ R < ∞ for the ground state and those excited states which dissociate into an atom and an ion in their ground states. The ground state potential curve for Cl2 has been calculated for R ∼ Re. Dissociation energies and other parameters obtained from the calculated potential curves are compared with corresponding parameters obtained from elastic differential scattering measurements and resonant electron capture in noble gases, measurements of afterglow line profiles in dissociative recombination radiation in neon and argon, optical absorption spectra of VK centers, and endoergic charge transfer studies of halogen ions and molecules. A formal analysis and discussion of the sources of correlation error in the calculated potential curves and a discussion of the expansion errors are also given.
Optical Activity as a Two-State Process
Authors: Power E. A. , Thirunamachandran T.
Published: February 2004

The phenomenon of optical activity is analyzed as a quantum two-state process with transitions between photon states of perpendicular plane polarizations, but with the same momentum. The matrix element connecting the two states is computed using quantum electrodynamics. The Rosenfeld—Condon formula for the angle of optical rotation is derived without recourse to Maxwell's equations. The relationship between refractive index and molecular polarizability is also derived using quantum electrodynamics. The theory is extended to obtain the difference between refractive indices of an optically active medium with respect to right and left circularly polarized light and the difference is related to optical rotation.
Absorption Spectra of Exciplexes
Authors: Potashnik R. , Goldschmidt C. R. , Ottolenghi M. , Weller A.
Published: February 2004

Absorption spectra of the exciplexes of pyrene, anthracene, biphenyl, and naphthalene with diethylaniline (DEA) as a common electron donor are recorded by applying pulse laser photolysis. The numerous bands appearing in the spectra are analyzed and attributed to transitions from the emitting charge-transfer state, (A−D+), to higher excited charge-transfer states [(A−*D+) and (A−D+*)], as well as to locally excited states [(A*D) and (AD*)]. The results indicate that exciplex absorption spectroscopy may provide a new route to the experimental observation of excited molecular states (of D or A), which are not detectable in the ground state spectra of the corresponding molecules.
Configuration Coordinate Model for the F Center in KBr
Authors: Jacobs P. W. M. , Menon A. Krishna
Published: February 2004

Experimental absorption curves for the F center in KBr, after correction for K-band absorption, have been analyzed in terms of the semiclassical configuration coordinate model with linear and quadratic coupling. This model fits the absorption data well at both the low-temperature and high-temperature limits. The best fit to the data is found by varying five parameters: These are the force constants in the ground and excited states, the photon energy corresponding to the maximum in the absorption band (Em), the relative displacement of the minima of the adiabatic potentials for the ground and excited states, and the effective frequency of the vibration which is coupled to the ground electronic state. Consistent values of the parameters are found at both temperature limits. An expression is derived for the shift of Em with temperature. It is pointed out that not only is Em not identical with the average photon energy but that its temperature dependence actually has the opposite sign. The theory is tested by predicting the temperature shift of Em; after suitable corrections for thermal expansion the agreement with experimental data is surprisingly satisfactory.
Diatomic Vibrational Potential Functions from Integration of a Poisson Equation
Authors: Anderson Alfred B. , Parr Robert G.
Published: February 2004

It is shown how to generate a diatomic vibrational potential W(R) from a knowledge of the effective electron density function F(R) which enters the Poisson equation ∇ 2W=F(R). Namely, W(R)=W(Re)+ ∫ ReR S(1−SR) F(S)dS.Using the fact that F(R) is at least roughly interpretable as proportional to the electron density at one nucleus due to the electron density following the other nucleus during vibration [A. B. Anderson and R. G. Parr, J. Chem. Phys. 53, 3375 (1970)], various reasonable forms for F(R) are proposed and tested. F(R) proportional to R−4 leads to a Fues potential. F(R) proportional to R−1exp(−η R) leads to a Hellmann potential. The simple assumption that F(R) is proportional to exp (−ζR) leads to a new potential which is a linear combination of terms R−1,  exp(−ζ R), and R−1 exp(−ζ R). Predictions of these three potentials are compared.
Vibrational Relaxation of Hydrogen Bromide in Gaseous Hydrogen Halide Mixtures
Authors: Chen Hao-Lin
Published: February 2004

A pulsed HBr chemical laser has been used to vibrationally excite HBr molecules in gaseous mixtures to their first vibrational excited state. The decay of infrared fluorescence following the laser pulse was studied. Cross sections for vibrational deactivation of HBr by HBr, HCl, n-H2, p-H2, and rare gases at room temperature have been found: σHBr–HBr = (4.5 ± 0.4) × 10−3 Å2,σHBr–HCl = (8.1 ± 0.9) × 10−3 Å2,σHBr–n-H2 = σHBr–p-H2 = (3.8 ± 0.2) × 10−4 Å2,σHBr–He ≤ (2.1 ± 0.2) × 10−5 Å2,σHBr–Ne ≤ (2.2 ± 0.2) × 10−5 Å2,σHBr–Ar ≤ (8.4 ± 0.7) × 10−6 Å2.The cross sections for vibration-to-vibration energy transfer from HBr to HCl and HI are σHBr–HCl = (4.56 ± 0.43) × 10−2 Å2 and σHBr–HI = (1.86 ± 0.24) × 10−1 Å2. The enhancement of probability for hydrogen halides at room temperature in Landau—Teller plots evident from extrapolating shock tube data available between 1800 and 800°K shows the importance of intermolecular forces. Direct comparison of vibrational relaxation rates among hydrogen halides (HCl, HBr, and HI) shows that the HCl–HCl interaction possesses a deeper attractive and steeper repulsive potential than HBr–HBr and HI–HI interactions. The small difference in cross section among rare gases indicates the unimportance of translational motion. Since equal cross sections are observed for n-H2 and p-H2, it is unlikely that energy is transferred into rotation of H2.
Absorption Band Profile of the Origin Region of the b Polarized 4000 Å Anthracene Crystal Transition
Authors: Morris G. C. , Rice S. A. , Sceats M. G. , Martin A. E.
Published: February 2004

New low temperature measurements of the reflectivity of crystalline anthracene are reported. Attention is confined to the important b axis polarized absorption band in the vicinity of the 0–0 transition. In this way line broadening by ``two particle'' excitations are eliminated. It is shown how low temperature reflectivity data, even when limited to only a region of the spectrum, can provide interesting information concerning the exciton dynamics. For this crystal transition optical constants are obtained from the observed reflectance data by use of a Kramers—Kronig analysis and a General Dispersion analysis. Discussed in some detail are those methods of obtaining optical constants, the values of the various band parameters and the implications of such values, the asymmetry of the absorption band profile and what that asymmetry may indicate. The interpretation of the data is not without its difficulties especially in view of the effects which may be caused by surface irregularities and by impurities and surrounding defects. Nevertheless, strong inferences are drawn from the measurements and their subsequent analysis. These include (i) the absorption coefficient in the b axis polarized 0–0 transition of crystalline anthracene is extremely large ∼1.6× 106 cm−1 at 7°K; (ii) the absorption line shape is asymmetric; (iii) the coupling between the exciton and optical phonons probably exceeds that between the exciton and acoustic phonons. The quantitative aspects of these observations are consistent with the strong coupling line shape theory of Fischer and Rice and of Grover and Silbey. The consequences of the analysis are employed to suggest areas for further experimental and theoretical work.
Kinetics of Electron Reactions in the γ Irradiated Liquids Ethane, Propane, Ethylene, Propylene, and Cyclopropane: Effect of Molecular Structure
Authors: Robinson M. G. , Freeman G. R.
Published: February 2004

The influence of molecular structure on the kinetics of electron reactions in liquids was studied by measuring the efficiency of electron scavenging in five C2 and C3 hydrocarbons at 183°K. γ radiation and nitrous oxide scavenger were used. The relative efficiencies of electron scavenging in the five liquids were in the decreasing order C2H6>C3H8>c–C3H6>C3H6>C2H4; choosing the efficiency in ethylene as unity, the relative values are about 40>17>2.7>1.3>1.0, respectively. The results are analyzed according to both the stochastic and the ``square root'' models for radiolysis kinétics. The conclusions drawn from the two models agree with each other. The smaller efficiency of electron scavenging in the olefins, compared to that in the alkanes, is mainly due to the shorter ranges of the secondary electrons in the olefins. Energy degradation of the secondary electrons in ethylene is an order of magnitude more efficient than it is in liquid ethane. The difference between the behavior of an electron in a liquid mono-olefin and that in the saturated analog decreases with increasing chain length. The behavior of cyclopropane falls between those of propane and propylene, which is consistent with the classical organic chemical reactivity of the compounds. There is no correlation between the electron range in the liquid and the magnitude of the permanent dipole moment of these molecules, but there is a correlation between the electron range and the nature of the polarizability of the molecules.
Temperature Dependence of the Spectral Intensity of the Fermi Resonant 1943 cm−1 Band of Carbonyl Fluoride
Authors: Adams Terry N. , Weston David M. , Matula Richard A.
Published: February 2004

The temperature dependence of the spectral and integrated intensity of the 1943 cm−1 infrared band of carbonyl fluoride was experimentally determined in the temperature range 300–600°K. The total integrated intensity, α1943, is independent of temperature and has a value of 4.04 ± 0.08 × 107cm−2 · (moles/cc) −1. An expression for the temperature dependence of the theoretical band shape of the ν2 fundamental vibration of carbonyl fluoride is presented, and numerical results based on this model are compared to the experimental data. Since the first overtone of the ν1 vibration is in Fermi resonance with the ν2 vibration, the temperature dependence of the Fermi resonant contribution was evaluated. The Fermi resonance effects were combined with the theoretical band shape to predict the spectral intensity of the 1943 cm−1 band at temperatures above 600°K.