bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase transition and melting pressures of solid ethane
Authors: Straty G. C. , Tsumura R.
Published: February 2003

The melting pressures of ethane at 14 temperatures from near the triple point to 95.50 K and pressures to 32.0 MPa are reported. A triple point temperature of 90.348±0.005 K is obtained from the data which is in agreement with the determination of Clusius and Weigand (1940) but in substantial disagreement with other determinations. Qualitative evidence has been obtained which indicates the existence of a previously unrecognized solid phase transition along a boundary roughly parallel to the melting line at a temperature about 0.5 K below the melting temperature, suggesting that some previous melting point determinations may have been influenced by a misinterpretation of the effects of this transition.
Collisional quenching of O(1S) by rare gas atoms and collision-induced emission by O(1S)-rare gas eximers
Authors: Welge K. H. , Atkinson R.
Published: February 2003

The quenching and collision-induced emission of the O(1S) atom by the rare gas atoms M=Xe, Kr, Ar, Ne, He has been investigated at 201 and 291 K. After pulsed photolytic production of O(1S) the emission decay rate as well as the intensity was investigated as a function of added gas concentration. Second-order O(1S) collisional quenching coefficients, kexp, and efficiency coefficients, k*exp, for the collisionally induced eximer emission have been measured. The formation of the O(1S)Xe eximer occurred with thermal equilibrium in the O(1S)Xe state by steady-state termolecular recombination, the O(1S)Xe potential well depth being ∼0.06 eV. For Kr, Ar, Ne,and He the quenching and emission enhancement did not exhibit a temperature dependence, showing that thermal equilibrium and steady-state recombination was applicable. The potential depths are small compared to kT, where T=201 K. The O(1S) removal occurs practically only via O(1S) + M (+ M ) ⇄krkf O(1S)M(+M), O(1S) M→A*O(1S)M+hv, with A* being an averaged molecular radiation probability. Other potential processes, in particular bimolecular quenching is unimportant. The mechanism is determined quantitatively by kexp=A⋅k*exp= A*⋅ (kf/kr) =A*⋅K, where K is the O(1S)M equilibrium constant, A the O(1D←1S) Einstein coefficient. From kexp, k*exp and K values for A* have been derived. Also upper limits of coefficients for the collisional removal of O(1S)M have been obtained. The numerical results are given in the paper.
Structural phase transitions in solids with applied stresses and fields, and effect of isotopic impurities on the free energy
Authors: Allen Roland E.
Published: February 2003

Subject to the assumptions described in the text, we obtain the following expression for the transition temperature Tc associated with a structural phase transition: Tc = α (ΔU + 𝒥iPiΔai)/kB, α ≡ 2/ln(‖Φ‖/‖Φ′‖). Here ΔU is the change in energy, the Pi are given by the pressure, stresses, and applied fields, the Δai are given by the changes in volume, strains, and dipole moments, and ‖Φ‖ is the determinant of the force constant matrix. We also give a result which may be useful for solids containing isotopic impurities: At high temperatures and in the harmonic approximation, ΔG = −(3/2) kBT 𝒥kln(mk′/mk), where ΔG is the change in Gibbs free energy when some of the particle masses are changed from mk to mk′.
A many-body approach to the vibrational structure in molecular electronic spectra. II. Application to nitrogen, carbon monoxide, and formaldehyde
Authors: Domcke W. , Cederbaum L. S.
Published: February 2003

The theory developed in the preceding paper is applied to calculate the vibrational structure in optical absorption and electron impact spectra of N2 and CO and in the photoelectron spectra of H2CO and D2CO. In addition, the vibrational structure of a recently measured shake-up line in the photoelectron spectrum of N2 is computed. The influence of anharmonicity effects on the Franck–Condon factors is discussed and a very simple scheme to take these effects into account is proposed. The one-particle approximation is shown to provide a fairly accurate picture in most cases. For formaldehyde many-body effects are incorporated into the vibrational coupling constants, leading to an improved agreement with experiment for all bands. The assignment of the third and the fourth ionization potential of formaldehyde, which has been controversial, is clarified.
Analytical equation for the Helmholtz free energy of a pure fluid, using the perturbation theory and a square well potential
Authors: Ponce Luis , Renon Henri
Published: February 2003

An analytical equation for the Helmholtz free energy of a pure fluid of particles interacting according to a square-well potential is derived from the Barker–Henderson perturbation theory. An analytical treatment of the solution of the Percus–Yevick integral equation for a fluid of hard spheres yields an analytical approximation for the integrals in the terms of the perturbation expansion.
A model three-dimensional pure substance with two critical points
Authors: Hecht Charles E. , Lind James
Published: February 2003

By softening the repulsive part of a model interparticle potential in three dimensions that also includes hard core and long range attractive parts, a second, high density–low temperature, critical point occurs in the thermodynamics of a one-component substance with such a potential as derived using first order perturbation theory. This model seems to account in a satisfactory qualitative way for the occurrence of certain isostructural electronic phase transitions in cerium and the alkali metals. Comparison is made between perturbation theory and the known exact results of Stell and Hemmer for the one-dimensional analog of the model.
Trajectory studies of unimolecular processes. II. Dynamics of chloroacetylene dissociation
Authors: Hase William L. , Feng Da-Fei
Published: February 2003

Lifetime distributions for H–C≡C–Cl with respect to dissociation were determined at 200, 175, and 150 kcal/mole. Both random and nonrandom sampling techniques were used. An analysis of distributions of internal coordinate energies shows that vibrational energy redistribution is nearly complete within 4.5×10−13 sec. The results indicate that H–C≡C–Cl is an ’’intrinsic’’ RRKM molecule in the 200–150 kcal/mole energy domain.
Configuration interaction calculations for 1E′ trimethylenemethane
Authors: Davidson Ernest R. , Borden Weston Thatcher
Published: February 2003

Complete pi-space CI calculations have been performed for the 1E′ state of trimethylenemethane in a planar D3h conformation using an STO-3G basis. Molecular orbitals were defined by SCF calculations with C2v symmetry constraints for the lowest 3B2 and 1B2 states. As expected, the 3B2 orbitals had nearly D3h symmetry while the 1B2 pi orbitals were severely distorted. Full pi-space configuration interaction calculations for both components of the 1E′ state using each set of molecular orbitals gave four nearly identical energies. This verified that the sigma cores from the two SCF calculations were essentially identical. The 1B2 component of the 1E′ wavefunction resembles an allyl radical plus an electron in a p orbital localized on one methylene group. Hence rotation of this methylene group into a plane orthogonal to the allyl radical should produce only a small change in energy.
Cross sections and rate constants for low-temperature 4He–H2 vibrational relaxation
Authors: Alexander Millard H. , McGuire Paul
Published: February 2003

Converged coupled-states integral cross sections were determined for the vibrational relaxation of the v=1 j=0 level of p-H2 in collisions with 4He. The collision energies ranged from 0.005 to 0.4 eV. The Gordon–Secrest (GS) potential was used with both a harmonic (HO) and rotating-Morse oscillator (MO) description of the H2 molecule. Additional calculations incorporated modifications in the long-range and spherically symmetric (V0) parts of the purely repulsive GS surface. Rotational coupling plays a major role in vibrational relaxation even at thermal energies. Although the relative importance of individual vibration–rotation transitions is a sensitive function of the choice of intramolecular potential, the HO and MO total relaxation cross sections are nearly identical. These total relaxation cross sections exhibit a power-law dependence on the initial translational energy down to ∼0.1 eV above threshold; below which point a positive curvature appears for all the surfaces considered. Rate constants for vibrational relaxation were computed and compared with experiment for 60 °K <T<500 °K. The GS rates lie below the experimental values and exhibit a less pronounced curvature at low temperatures. Introducing the correct long-range attraction into the GS V0 potential results in a modest increase in curvature. Agreement with experiment is obtained only with the use of the semiempirical V0 potential of Shafer and Gordon.
On the significance of finite propagation speeds in multicomponent reacting systems
Authors: Othmer H. G.
Published: February 2003

A continuum model of diffusion in a reacting mixture is built around a constitutive relation for momentum exchange by frictional interaction between diffusing species. The resulting continuity and momentum equations incorporate a finite relaxation time for diffusion. Under appropriate conditions, linearization of these equations produces a coupled system of hyperbolic equations for small disturbances of a stationary state. Fick’s law can be recovered from the linear equations by assuming instantaneous relaxation of the flux, provided that the stationary state is uniform. Fick’s law is generally inconsistent with the momentum equation when the stationary state is nonuniform. The stability of uniform stationary solutions predicted by the parabolic system obtained when Fick’s law is used is compared with the stability predicted by the hyperbolic system. When the former predicts stability and has at least one pair of complex-conjugate roots, the latter may predict that the stationary state is unstable. Thus, inclusion of relaxation in the model can lead to qualitatively different predictions of stability.
Spin–rotation measurements and magnetic shielding in CH2CF2
Authors: Casleton K. H. , Gierke T. D. , Wang J. H.-S. , Kukolich S. G.
Published: February 2003

Rotational transitions 101→000, 212→111, 211→212, and 321→322 of 1,1 difluoroethylene were studied using a molecular beam maser spectrometer. Emission transitions were observed with 6 kHz linewidth (FWHM) and hyperfine structure due to fluorine and hydrogen interactions was resolved. The diagonal elements of the fluorine spin–rotation tensor are Maa=−13.4±3.6 kHz, Mbb=−10.94±0.68 kHz and Mcc=−6.06±0.68 kHz. This data is used to determine paramagnetic contributions to the fluorine chemical shift tensor. Analysis of the data yielded line centers for the rotational transitions of 15 774 348±3 kHz for 101→000, 26 465 055±5 for 212→111, and 14 419 906±3 kHz for 321→322, and 15 250 615±3 kHz for 211→212. Results of semiempirical calculations of diamagnetic contributions to the shielding tenors are presented for CH2CF2 and other molecules. Comparisons of total shielding tensors are made for related molecules.
Modified ’’ideal three phase model’’ and the melting of alkali metals
Authors: Rosenfeld Y.
Published: February 2003

A model potential for real materials is proposed that consists of inverse-power, 1/rn, repulsion with a density dependent power, n (ρ), and Kac attraction, −γ3 exp(−γr). The function n (ρ) is determined semiempirically from compressibility factor data along the melting line. The model is applied to the alkali metals and is capable of reproducing the Kraut–Kennedy law and the maximum in the melting curve.
On the hyperfine splitting of the hydrogen atom in a spherical box
Authors: Suryanarayana D. , Weil J. A.
Published: February 2003

The hyperfine splitting of the hydrogenlike atom confined to a sphere of radius r0 is examined as a function of r0. The wavefunction is made to vanish at r=r0 and is normalized to unity over the finite sphere. The effect of decreasing r0 (i.e., compressing the sphere isotropically) on the hyperfine splitting A of the ground state is nonlinear, with A increasing approximately as r−10. Comparison with atomic hydrogen trapped in α-quartz is made.
The chemistry of chromyl fluoride. IV. Raman spectrum of CrO2F2 in the solid and liquid phases
Authors: Brown Steven D. , Gard Gary L. , Loehr Thomas M.
Published: February 2003

Raman spectra are reported for liquid and solid chromyl fluoride. Nine Raman lines, of which four are polarized, are observed for CrO2F2(l) and assigned to a monomeric structure possessing C2v symmetry. Some reassignments for previously reported gas phase infrared bands are suggested based on the new Raman data. The symmetric Cr–F stretching vibration at 708 cm−1 in CrO2F2(l) disappears in the spectrum of the solid phase material, which has a new Raman line at 540 cm−1 characteristic of extensive fluorine bridge bonding.
Negative gaseous ions from nitric acid
Authors: Mathur B. P. , Rothe Erhard W. , Tang S. Y. , Mahajan Kanwal , Reck Gene P.
Published: February 2003

A crossed-beam system of Cs atoms and HNO3 molecules has been used to study the ion chemistry of HNO3. The existence of an HNO2− anion was observed and EA(HNO3) and D(H–ONO2−), the electron affinity of HNO3, and the dissociation energy of the parent anion were measured. Also, value for EA(NO3) was deduced which requires additional thermodynamic data and compare it with previous work. (AIP)
Energy loss spectra of K+ ions (0.1–1.0 keV) in collision with N2 molecules
Authors: Inouye H. , Niurao K. , Sato Y.
Published: February 2003

The energy loss spectra of K+ ions (E0=0.1-1.0 keV) scattered by N2 molecules is reported for the laboratory angle range of 1–18°. (AIP)
Comment on ’’Inelastic scattering in atom–diatomic molecule collisions. I. Rotational transitions in the sudden approximation’’
Authors: Pack Russell T
Published: February 2003

It is argued that conflicting approximations in a recent paper [J. R. Stallcop, J. Chem. Phys. 61, 5085 (1974)] render the resulting theory invalid. (AIP)
Inelastic collisions between an atom and a diatomic molecule. III. Comparison of approximation methods as applied to the H+H2 rotational excitation
Authors: Choi B. H. , Tang K. T.
Published: February 2003

The close coupling method is used to calculate the rotational excitation cross sections of H+H2 collisions. On the potential surface suggested by Chu and Dalgarno, close coupling results are compared with results of distorted wave Born approximation and of effective close coupling approximation. On the potential surface suggested by McGuire and Krüger, close coupling results are compared with results of DWBA and of Jz-conserving coupled states approximation. The simple DWBA is generally adequate for this system, and in some cases, it is much better than other approximation methods. A third potential based on the experimental V0 of Gegenbach, Hahn, and Toennies and the nonempirical V2 of Norbeck, Certain, and Tang is also used. The excitation cross sections are smaller by orders-of-magnitude than the ones determined on the other two surfaces.
SPIN–CIPSI calculations on H2CO
Authors: Gouyet J. F. , Prat M. T.
Published: February 2003

The efficiency of configuration interaction by perturbation with spin eigenfunctions is discussed in the case of ground and excited states of formaldehyde in its ground state equilibrium conformation. Two extensive configuration interactions using for every excited state more than 40 000 configurations eigenfunctions of spin, including six open shells, is carried out using the spincip program, spin-symmetry-adapted generalization of cipsi.
Some consequences of molecular symmetry in the theory of photoelectron angular distributions
Authors: Druger S. D.
Published: February 2003

The molecular photoelectron angular distribution is treated by regarding the ionization process as a coherent superposition of component transitions, each having specific molecular symmetry transformation properties. The symmetry-related properties of the resulting contributions and the selection rules that govern their occurrence in some specific ionization models are examined, and a generally applicable rule is obtained requiring interferences between ionization components with appropriate molecular symmetry transformation properties to vanish identically. Application of molecular symmetry methods to the angular momentum transfer formulation leads to the development of methods for generating angular-momentum-transfer selection rules. These methods are applied to direct ionization in an orbital approximation for 40 symmetries and for the general case of an n-fold rotational symmetry, and meaningful restrictions on the allowed values of the angular momentum transfer are shown to apply even to some low symmetry systems.
Two-body clusters in quantum statistical mechanics
Authors: Berman D. H. , Bruch L. W.
Published: February 2003

The mass derivative of the direct second virial coefficient is shown to be negative and the two-body direct term in the kinetic energy density expansion is shown to be positive.
Thermal diffusion factors for binary noble gas mixtures from column measurements. II
Authors: Santamaría C. M. , Savirón J. M. , Yarza J. C. , Carrión J. A.
Published: February 2003

A set of measurements of the thermal diffusion factor of the gaseous binary mixtures Kr–Xe, Ar–Xe, Ar–Kr, Ne–Kr, Ne–Ar, He–Kr, and He–Xe at ?=340.±5.K are presented. The measurement apparatus is a concentric-tube type thermal diffusion column, calibrated in a previous work with mixtures of He–Ar. It is shown that with the αT measurement method used, one obtains relative αT values that fit the Laranjeira criterion and are consistent with the most reliable literature values.
Analytic structure of the eigenvalue problem as used in semiclassical theory of electronically inelastic collisions
Authors: Pechukas Philip , George Thomas F. , Morokuma Keiji , McLafferty Francis J. , Laing John R.
Published: February 2003

The analytic properties of eigenvalues and eigenvectors of analytic symmetric matrices of arbitrary size are discussed, with special attention given to the branch point structure at a degeneracy of two eigenvalues—that is, at a complex crossing point of two potential surfaces. The discussion is relevant to semiclassical theory of electronically inelastic collisions.
Formation of nitrous oxide in the reaction of O(1D2) atoms with nitrogen
Authors: Kajimoto O. , Cvetanović R. J.
Published: February 2003

The quantum yields of N2O (φN2O) formed in the reaction of O(1D2) atoms with N2 have been determined in the gas phase at 23°C and at pressures between 25 and 115 atm and, for comparison, in liquid phase at cryogenic temperatures. Extrapolation of the gas phase results indicates for φN2O at 1 atm the very low value of 3×10−7, which precludes direct observation of N2O formation at 1 atm in laboratory experiments by the currently employed analytical techniques. With increasing pressure φN2O increases but does not show the simple dependence on [N2] predicted by the generally used mechanism based on the ’’strong collision’’ assumption. The results show instead a linear dependence of 1/φ1/2N2O on 1/[N2], which can be rationalized in terms of two alternative mechanisms. Although both mechanisms invoke a two stage deactivation of the energy rich initial adduct (N2O*), they differ in some important respects. The effects of additions of O2 and Ar have been also studied and can be explained well by the same two mechanisms but do not differentiate between them within the range of experimental conditions employed.
Volta effect and liquidlike layer at the ice surface
Authors: Mazzega E. , del Pennino U. , Loria A. , Mantovani S.
Published: February 2003

The Volta potential difference between Ih ice single crystals and different metals has been measured as a function of the temperature by using the vibrating electrode technique. Reproducible results have been obtained with ice–gold and ice–copper contacts, indicating that in these cases the equilibrium has been attained. At temperatures below −30 °C the dependence is linear, and we think that this is the effect of the impurity content on the ice Fermi level. At higher temperatures a term which is logarithmic in (Tm−T), where Tm is the melting temperature of ice, is added. This additional pd has proved to be localized at the ice surface and ranges from 0 to 150 mV; it can be directly related to the appearance and thickening of the polarized, liquidlike layer predicted by N. H. Fletcher, if we assume that a constant electric field exists in the layer interior. The preferred dipole orientation turns out to be that with the oxygens outwards. We also obtained the approximate value of 4.3 eV for the ice work function.
Collision dynamics of three interacting atoms: Stripping reactions of Ar++H2 and of K+I2
Authors: Yuan Jian-Min , Micha David A.
Published: February 2003

Equations for stripping reaction cross sections, obtained from a multiple-collision expansion for triatomic systems, are applied to Ar++H2 → ArH++H and its isotopic substitutions, and to K+I2 → KI+I. The equations involve the momentum distributions of reactant and product molecules, and are considered for mechanisms where stripping begins either before or after electron transfer, for both systems. Calculations of forward velocity distributions, product angular and energy distributions, isotope ratios, and total cross sections for Ar++H2 are in over-all agreement with experiments and indicate that stripping begins after electron transfer in these systems. Comparison with experiment of calculated product angular and energy distributions and forward velocity distrubutions for K+I2 favors a mechanism where a vertical electron transfer occurs first, with simultaneous partial vibrational relaxation of I−2, followed then by stripping. Discrepancies remain however for K+I2, suggesting some contribution from other mechanisms.
On the theory of diffraction of Maxwellian atomic beams by solid surfaces
Authors: Goodman Frank O.
Published: February 2003

In the context of diffraction of Maxwellian (thermal) atomic beams by solid surfaces, the usual assumption that the angular position of the maximum in a diffracted beam corresponds to the diffraction angle of atoms with the most probable de Broglie wavelength is examined, and compared with other possible criteria and with the correct result. It is concluded that, although this criterion may be the best simple one available, it is certainly bad in some situations; the reasons why, and the conditions under which, it is expected to be good are discussed. Also, it is shown that considerable care must be taken when shapes of diffracted beams and when angular positions of their maxima are calculated, because certain physical effects (which are always present) may change these shapes and positions in unexpected ways. The theory is compared with two sets of relatively modern experimental data, one set for which the fit is good, and another set for which a fit is impossible.
Topological index as applied to π-electronic systems. III. Mathematical relations among various bond orders
Authors: Hosoya Haruo , Hosoi Kikuko
Published: February 2003

Mathematical relations among the Coulson (pCl), Ham and Ruedenberg (pHRl), Pauling (pPl), and topological (pTl) bond orders have been derived by combining the enumeration technique of the graph theory and the complex integral developed by Coulson and Longuet-Higgins. If one defines a function FG,l(y) for bond l of graph G as FG,l(y) =Δr,s(iy)/Δ (iy)(l=rs¯) the following relations are proved for alternant hydrocarbons: pCl=2/πℱ∞0FG,l(y) dy, pHRl=pPl=FG,l(0), pTl=FG,l(1) for tree graphs, pTl=FG,l(1) for nontree graphs. Linear relationship pCl∝pTl+ApPl (A≪1) is also proved. Abnormal bond orders for 4n-membered ring systems are discussed. Graphical methods for decomposing determinants and adjuncts are proposed.
Bound and quasibound states of alkali–rare gas molecules
Authors: Goldhor Richard , Pritchard David
Published: February 2003

Numerical calculations of bound and quasi bound states of alkali–rare gas van derm Wails molecules are presented. Computational precautions which must be taken when solving for high-lying bound states and also for quasi bound states are outlined. We present calculations for Kr using several potentials to illustrate the effects of different potential shapes on the number of states. The calculated lifetimes of quasi bound levels are shown to vary over such a wide range that some, but not all, of the quasi bound molecules will behave like bound molecules in most conceivable physical situations. Our results verify the accuracy of analytic methods proposed by Mahan and Lapps for estimating the number of bound states in Leonard-Jones potentials.
A forbidden singlet–triplet anticrossing in D2
Authors: Miller Terry A. , Freund Robert S. , Zegarski Bernard R.
Published: February 2003

Anticrossings have been observed between the v=4, N=2, G (3d) 1Σg and v=0, N=2, r (4d)3Πg states of D2. These anticrossings fall into two distinct sets, fairly weak and quite narrow (<15 G) anticrossings induced by spin–orbit coupling and stronger and broader (∼100 G) anticrossings introduced by the Fermi contact hyperfine interaction. Analysis of the positions of the anticrossings has allowed an accurate determination of the levels’ zero field separation, the g factors of both the singlet and the triplet, and the quadratic Zeeman parameters for both the singlet and triplet. Hyperfine structure is also observed in four of the anticrossings which provides a measure of the diagonal Fermi contact interaction in the 3Π state. The widths of the anticrossing curves provide values for the spin–orbit and the Fermi contact perturbations between the two states.
Determination of the lateral diffusion coefficient of potassium oleate in the lamellar phase
Authors: Roeder Stephen B. W. , Burnell E. Elliott , Kuo An-Li , Wade Chas. G.
Published: February 2003

Constant gradient and pulsed gradient NMR spin echo methods have been used to measure the diffusion constant of potassium oleate in the lamellar phase. Oriented samples were employed and yielded a mean value of ?1×10−6 cm2/sec at 29 °C for the diffusion constant parallel to the lamellar surface.
Charge transfer reactions of atomic ions with polyatomic molecules
Authors: Hedrick A. F. , Moran T. F.
Published: February 2003

A time-of-flight technique has been used to measure the fast neutral Ar0 products from charge transfer reactions of Ar+(2P1/2, 2P3/2) ions with neutral CO2, CH4, C2H4, and C2H6 molecules. Reaction cross sections were found to be independent of the electron energy (from threshold to 100 eV) used to produce reactant ion beams and indicates that essentially all the Ar+ ions in the experimental apparatus are in the ground 2P state prior to reaction. (AIP)
Piecewise analytic wavefunctions for bound states and scattering
Authors: Rosenthal Alan , Gordon Roy G.
Published: February 2003

Methods presented previously [J. Chem. Phys. 51, 14 (1969); Methods Comput. Phys. 10, 81 (1971)] for constructing piecewise analytic (Airy function) solutions to the close-coupled equations of molecular scattering and bound states are reviewed and developed further. The original formalism is rederived using Green’s function techniques. The first order perturbation integrals are rewritten in a more compact and numerically stable form. A quadrature is presented for integrating products of wavefunctions of unequal diagonal slopes. Numerically efficient techniques are presented for constructing single channel bound state functions and using them in matrix element and overlap integrals.
Coordinate systems for colinear inelastic and reactive scattering defined by conformal transformation
Authors: Rosenthal Alan , Gordon Roy G.
Published: February 2003

In order to build wavefunctions for colinear reactive scattering from solutions of a one-dimensional Schrödinger equation, it is necessary to change the coordinate system from mass-weighted Jacobi coordinates (x,y) to a system of reaction coordinates that retains the ∇2 character of the kinetic energy operator. Connor and Marcus [J. Chem. Phys. 53, 3188 (1970)] proposed a conformal transformation that maps an infinite chevron in the complex Jacobi coordinate z=x+iy plane to an infinite strip in the w=u+iv plane. u is the reaction coordinate; v is the (generalized) vibrational coordinate. We show that computational difficulties associated with this transformation can be partially removed by either of two methods of mapping part of the w-plane strip into an infinte strip in a third plane, t=r+is. The first method introduces ’’dipole pairs’’ in the w plane. The second introduces a slit in the w-plane strip. Relative advantages of the two methods are discussed. A Connor–Marcus-like map from a semi-infinite trapezoid to a semi-infinite rectangle is also derived for inelastic scattering calculations.
Quantum colinear inelastic and reactive scattering with piecewise analytic wavefunctions
Authors: Rosenthal Alan , Gordon Roy G.
Published: February 2003

Piecewise analytic scattering wavefunctions are constructed for colinear models of inelastic and reactive scattering systems, using piecewise analytic vibrational basis sets and reaction coordinates defined by conformal transformations. Various approximate and exact methods for computing basis transformation matrices are discussed. Also presented are a compact formalism for extracting transmission and reflection coefficients (S-matrix elements) from the wavefunctions, and a method for transforming the wavefunctions from one coordinate system to another. Model potential surfaces used include two models of inelastic scattering (harmonic oscillator–exponential repulsion and harmonic oscillator–Lennard-Jones) and a colinear Porter–Karplus H3 surface. Transmission and reflection probabilities from converged close-coupled calculations on the latter surface from threshold to −3.1 eV are presented. The number of closed channels used and the calculated probabilities are consistent with previously reported calculations.
Intermolecular potential surfaces from electron gas methods. I. Angle and distance dependence of the He–CO2 and Ar–CO2 interactions
Authors: Parker Gregory A. , Snow Richard L. , Pack Russell T
Published: February 2003

Angle dependent intermolecular potential energy surfaces suitable for use in studies of rotationally inelastic collisions of rigid linear CO2 with Ar and He are calculated using the electron gas model to obtain the short range interactions and joining them smoothly to the long range van der Waals tails of the preceding paper. Smooth analytic fits to the potentials, convenient for use in scattering calculations, are given. The surfaces are very strongly nonspherical. Virial coefficients calculated using the a priori He–CO2 potential are in excellent agreement with experiment, and a simple adjustment of the Ar–CO2 potential gives excellent agreement with both virial coefficients and a potential inferred from high energy scattering data.
Light-induced displacement of hydrogen in pyrimidine H-addition radicals
Authors: Flossmann W. , Westhof E. , Müller A.
Published: February 2003

After x irradiation of single crystals of 1-CH3-uracil, 1-CH3-uracil⋅HBr, cytosine⋅H2O, and deoxycytidine⋅HCl at room temperature C5-addition radicals, which result from H addition at carbon 5 of the unsaturated C5–C6 bond of the pyrimidine ring, are formed. It is shown that, upon irradiation with light of wavelength λ≳400 nm, these radicals transform into C6-addition radicals where the added hydrogen atom is localized on carbon 6. INDO calculations show that, whereas C5-addition radicals are neutral, the C6-addition radicals must be positively charged in order to reproduce the experimental couplings.
The group function model. A set of orthogonality conditions
Authors: Wilson Stephen
Published: February 2003

Some aspects of the group function model for molecular electronic wavefunctions are examined. Using a spin–free formalism, a set of orthogonality conditions for group functions is obtained. Each of these conditions corresponds to a certain degree of interaction between the groups of electrons. The strongly orthogonal group function model, the weakly orthogonal group function model, and the ’’loge’’ model emerge as special cases.
Low-energy differential elastic scattering of Ne* (3P) by Kr(1S)
Authors: Winicur Daniel H. , Fraites James L. , Bentley John
Published: February 2003

Differential elastic cross sections for Ne* (3P) scattered by Kr are obtained at three relative kinetic energies, 64 to 74 meV. Location and shape of rainbow maxima, observed at all energies, are used to determine the well depth and potential minimum for a double-Lennard-Jones potential. The results, ε=8.05±0.49 meV, and rm=4.91±0.64 Å are similar to those for Na+Kr and are substantially different from those of Ne+Kr. A value of 2.11 Å for the atomic radius of Ne* is obtained which is close to that previously reported for Na.
Quantum-mechanical treatment of Eu+3 4f→4f and 4f?charge-transfer-state transitions in Y2O2S and La2O2S
Authors: Struck C. W. , Fonger W. H.
Published: February 2003

The quantum-mechanical single-configurational-coordinate model is used to interpret Y2O2S:Eu+3 and La2O2S:Eu+3 7F→charge-transfer state (CTS) absorption, 5Di→5Di−1 one-step and 5D→CTS→5D two-step quenchings, and CTS→5Di feeding fractions. The preferred fit requires unequal force constants and a small downshifting of the CTS parabola with increasing temperature.
Linewidths in OCS: Isotope effects, vibrational effects, temperature dependence, and T1/T2
Authors: Creswell R. A. , Brown S. R. , Schwendeman R. H.
Published: February 2003

A computer-controlled microwave spectrometer has been used to record the frequency dependence of the absorption of the J=2←1 transition of OCS under varying conditions of pressure, temperature, and microwave power. From least-squares fits of the data to Lorentzian line shapes, a variety of linewidths and linewidth parameters have been deduced. The linewidth parameter for the J=2←1 transition of 16O12C32S in the ground vibrational state has been determined to be 6.03±0.05 MHz/torr. The ratios of linewidth parameters for this transition for several other species to that for the ground state of 16O12C32S are: 16O12C34S, ground state, 0.987±0.003; 16O13C32S, ground state, 0.991±0.005; 18O12C32S, ground state, 0.966±0.018; 16O12C32S, v3=1, 1.024±0.026; 16O12C32S, v2l=2°, 0.978±0.003. The linewidth parameter for the ground state of the parent species was determined to be inversely proportional to the absolute temperature in the range 297–346 K. From comparison of theoretical and experimental power-broadened lineshapes it is shown that T1/T2=1.04±0.10 for the transition.
Lithium isotope separation factors of some two-phase equilibrium systems
Authors: Palko A. A. , Drury J. S. , Begun G. M.
Published: February 2003

Isotope separation factors of seventeen two-phase equilibrium systems for lithium isotope enrichment have been determined. In all cases, lithium amalgam was used as one of the lithium-containing phases and was equilibrated with an aqueous or organic phase containing a lithium compound. In all systems examined, isotopic exchange was found to be extremely rapid, and 6Li was concentrated in the amalgam phase. The isotopic separation factor for the LiOH(aqueous) vs Li(amalgam) system has been studied as a function of temperature from −2 to 80 °C. The values obtained have been compared with the ’’electrolysis’’ and exchange separation factors given in the literature. The two-phase systems, LiCl(ethylenediamine) vs Li(amalgam) and LiCl(propylenediamine) vs Li(amalgam), have been studied, and the isotopic separation factors have been determined as functions of the temperature. The factors for the two systems have been found to be substantially the same (within limits of the errors involved) over the temperature range studied (0 to 100 °C) as those for the aqueous system. The isotopic separation factors for the seventeen systems have been tabulated, and correlations have been drawn that show the salt and solvent effects upon the values obtained.
Transformation of the Chandler–Andersen RISM equation for fluids of diatomic molecules
Authors: MacInnes D. A. , Farquhar I. E.
Published: February 2003

The reference interaction site model (RISM) equation of Chandler and Andersen [J. Chem. Phys. 57, 1930 (1972)] is transformed by means of a technique of Wertheim [J. Math. Phys. 5, 643 (1964)] into a form which involves the indirect correlation function over a reduced range. It is expected that, as with Baxter’s form of the Ornstein–Zernike equation [Phys. Rev. 154, 170 (1967); Aust. J. Phys. 21, 563 (1968)], this reduction will facilitate numerical solution of the RISM equation.
Transverse collective modes in liquid pyridine by depolarized light scattering
Authors: Searby G. M. , Bezot P. , Sixou P.
Published: February 2003

We have observed the existence of collective transverse behavior in liquid and supercooled phases of a symmetric top: Pyridine. The HH fine structure is particularly well resolved and is visible over a wider temperature range than the VH fine structure. We analyze both spectra in terms of the theory of Keyes and Kivelson and find that the value of the coupling parameter as deduced from the HH spectra has approximately twice the value of the corresponding parameter from the VH spectra.
On simple saddle points of a potential surface, the conservation of nuclear symmetry along paths of steepest descent, and the symmetry of transition states
Authors: Pechukas Philip
Published: February 2003

We show that if the transition state of a chemical reaction is a simple saddle point of the potential surface linked directly with reactants and products by paths of steepest descent, then the symmetry of the transition state is limited to the joint symmetry of reactant and product, unless reactant and product are physically indistinguishable and themselves symmetry related, in which case the transition state may have those additional symmetries that interchange reactant and product. We outline some of the general consequences of this symmetry restriction on transition states.
Emission spectrum of aluminum in a laser-produced plasma
Authors: Wei P. S. P.
Published: February 2003

The emission spectrum of AlI generated by a CO2 laser pulse from an alumina surface in air has been studied with Kodak SWR plates. In addition to the 4p, 5p, and 4f forbidden transitions previously observed, forbidden lines from 6, 7, 8p and from 5, 6, 7f states to the 3p ground state are identified. Photoelectric measurements yield information concerning the plasma relaxation time. In the present experiments, Al and AlO are found to last for 150 and 500 μsec, respectively, after the start of the 25 μsec pulse.
Anisotropic motional averaging in a constrained polymer chain
Authors: Douglass D. C. , McBrierty V. J. , Weber T. A.
Published: February 2003

The NMR linewidth of Kel–F fibers is unusual in that the component assigned to the amorphous regions of this semicrystalline polymer exhibits anisotropy as a function of fiber orientation with respect to applied magnetic field at temperatures near 140 °C. This feature is attributed to anisotropy in the motion of folds on lamellar surfaces. A model based upon a wormlike chain, with ends constrained to a plane surface, adequately describes the experimental observations.
Scattering of high-velocity Ar atoms by CO2, OCS, and CS2
Authors: Amdur I. , Peters W. A. , Jordan J. E. , Mason E. A.
Published: February 2003

Fast Ar beams have been scattered by room-temperature CO2, OCS, and CS2 to obtain average atom–molecule potentials. The results are consistent with other scattering measurements on similar systems, and are also in excellent agreement with available theoretical calculations based on an electron–gas model. Decomposition of the atom–molecule potentials into constituent atom–atom potentials shows that such a representation can be utilized with fair accuracy but that a definite discrepancy exists.
Deactivation of HCl(v=1) and DCl(v=1) by H and D atoms at T=295 K
Authors: Bott J. F. , Heidner R. F.
Published: February 2003

The techniques of isothermal calorimetry (for H atoms) and laser-induced fluorescence [for HCl(1)] were combined to yield absolute rate coefficients for H and D atom removal of HCl(1) and DCl(1). At T=295 K, the rate coefficients for H+HCl(1), D+HCl(1), H+DCl(1), and D+DCl(1) are (4.6±1.4) ×1012, (6.5±2.0) ×1012, (1.1±0.3) ×1012, and (1.2±0.4) ×1012 cm3/mol⋅sec, respectively.
Liquid water as a lone-pair amorphous semiconductor
Authors: Williams Ferd , Varma S. P. , Hillenius S.
Published: February 2003

We approximate liquid water as a lone-pair amorphous semiconductor. Since electronic orbital times are short compared to the periods of atomic and molecular motion, properties dependent on electronic states can be interpreted to determine short-time intermediate range order. An anomalous temperature dependence of the Urbach exponential absorption edge for intramolecular electronic excitation is noted and interpreted in terms of the perturbation of the lone-pair valence band by hydrogen bonding. The extrinsic optical absorptions with I− and Br− doped water are observed to have Urbach tails. An approximate electronic band structure for pure and doped liquid water is presented.
Field-dependent mobility in liquid hydrocarbons
Authors: Funabashi K. , Rao Bappanadu N.
Published: February 2003

The field-dependent electron mobility for low-mobility liquid hydrocarbons is studied using a phenomenological model, in which the electron transport takes place by a hopping mechanism over multiple barriers with fluctuating heights. It is shown that the simple hyperbolic sine law for a nonlinear conductance with uniform barrier heights predicts a jump distance several times larger than the true jump distance of the hopping motion. With a uniform distribution and a binary distribution for the barrier height, reasonable agreement with the experiments of Bakale, Sowada, and Schmidt is obtained with a smaller value of the jump distance.
Molecular dynamics study of an amorphous Lennard-Jones system at low temperature
Authors: Rahman A. , Mandell M. J. , McTague J. P.
Published: February 2003

Using molecular dynamics techniques, low temperature properties of a 500-particle amorphous system of Lennard-Jones particles have been studied. The system was prepared by rapid quenching of an originally liquid sample. The structural properties are similar to those of random close-packed hard spheres. Propagating longitudinal phonons are observed even at fairly short wavelengths and well defined transverse phonons are found at the longest wavelengths available. Some preliminary results for the ’’glass transition’’ region are reported.
Molecular orbital calculations of quadrupolar coupling of 11B in molecular models of glasses
Authors: Snyder Lawrence C. , Peterson G. E. , Kurkjian C. R.
Published: February 2003

SCF–MO calculations have been made for borate glasses using B(OH)3 and BH3 as molecular models. These calculations have shown the triangular configurations to be quite stable with large energies required for out-of-plane distortions. Variations in the positions of nearest neighbor triangles or other neighboring charges can cause a spread in quadrupole coupling constant consistent with the experimental data. Smaller spreads in coupling can be brought about by changes in B–O bond lengths within the BO3 triangles. Gross bending of the triangles causes only very small changes in coupling.
New formula to estimate the ground state energy, E
Authors: Thomas Gerald F. , Javor Frank , Rothstein Stuart M.
Published: February 2003

The one-electron reduced local energy function, EL(1), is introduced which has the properties 〈EL〉=〈H〉, and 〈E2L〉 ⩽〈H2〉. It is suggested that the accuracy of EL reflects the local accuracy of an approximate wavefunction. From the properties of EL a modified form of Weinstein’s formula, Ew′, is defined which is bounded as follows: Ew⩽Ew′⩽〈H〉, where Ew is Weinstein’s lower bound formula for the ground state energy, E0. The estimate to E0 provided by Ew′ is not guaranteed as an upper or lower bound, but it provides a useful adjunct to 〈H〉 which does not require 〈H2〉. Applications to a variety of approximate wavefunctions for X 1Σ+g H2 and 1 1S He are presented.
Polarizability and dielectric properties of helium
Authors: Kirouac Serge , Bose T. K.
Published: February 2003

A precise measurement of the dielectric second virial coefficient of helium gives a value which compares very favorably with the previously determined experimental value of Orcutt and Cole. The dielectric third virial coefficient agrees reasonably well with the calculation of Heller and Gelbart based on the Hartree–Fock theory.
Phase diagram of ammonium iodide obtained by Raman spectroscopy under hydrostatic pressure
Authors: Hochheimer H. D. , Spanner E. , Strauch D.
Published: February 2003

The Raman spectra of ammonium iodide have been measured under hydrostatic pressure up to 6.4 kbar and at temperatures between 130 and 300 K. The strong change of the Raman spectra of NH4I allows the determination of the phase diagram of NH4I. The triple point is found to be at 5.5±0.1 kbar and 170±2 K. The temperature and pressure hysteresis at the triple point is between 3 and 4 K and 100 and 200 bar.
Study of phase transitions and of the possible existence of a fifth phase in NH4Br by Raman scattering under high pressure
Authors: Hochheimer H. D. , Geisel T.
Published: February 2003

We have investigated phases II, III, IV, and the previously suggested phase V in NH4Br under high pressure by Raman scattering experiments. The pressure and temperature dependences of band intensities and frequencies at the transitions are discussed. The possible existence of a fifth phase is examined by comparison with calculated Raman spectra for different types of ordering. These calculations show that the spectra in the range of phase V reported in the present and in all former Raman investigations are due to the same type of ordering as in phase IV. As there is no indication of a transition from phase IV, we conclude that phase IV is present where phase V was suggested. The same conclusion can be inferred from all other high pressure Raman scattering studies so far reported. The fifth phase, originally observed by ultrasonic measurements, might have been a property of the particular sample.
Reduction of adenine dihydrochloride by ionizing radiation
Authors: Box Harold C. , Budzinski Edwin E.
Published: February 2003

The reduction product produced by ionizing radiation in single crystals of adenine dihydrochloride x irradiated at 4.2 °K was studied by ESR–ENDOR spectroscopy. Addition of an electron to the protonated base yields a free radical with a spin density of approximately 0.30 on the C-8 carbon atom. The spin density was inferred from ENDOR measurements of the hyperfine coupling of the C8–H proton.
Negative ion formation in halocarbons by charge exchange with cesium
Authors: Tang S. Y. , Mathur B. P. , Rothe Erhard W. , Reck Gene P.
Published: February 2003

A crossed molecular beam apparatus is used to study the formation of anions by charge exchange of fast cesium atoms with a variety of halocarbons. The branching ratios are determined from threshold to 350 eV. Comparison of the spectator stripping and information theoretical models to the data leads to the conclusion that this class of reactions is an example of an ultradirect impulsive mechanism. In the most favorable case, that of CF3I, we have determined the near threshold relative cross sections for the anions CF3I−, I−, CF−3, and IF−. From these we determine the electron affinity of CF3I− to be 1.4±0.2 eV and the bond dissociation energy of CF3-I− as 0.38±0.1 eV, which disagrees with values obtained in a previous experiment.