bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraviolet emission from magnesium atoms isolated in rare gas matrices
Authors: Knight L. B. , Brittain R. D. , Starr M. A. , Joyner C. H.
Published: February 2004

Ultraviolet emission from argon and krypton matrices at 4.2 and 12°K containing trapped magnesium atoms has been observed at 2970 and 3236 Å, respectively. Magnesium atoms trapped in nitrogen, neon, and argon matrices containing more than 10% nitrogen do not show such emission. Evidence is presented which indicates that the emission bands result from excitation of the 1P ← 1S magnesium atomic absorption band at 2815 Å in argon. Several different proposals to account for the emission band are presented, including possible Mg2 transitions, electron-phonon coupling effects, and interactions between excited magnesium atoms and rare gas atoms.
Proton NMDR of ethylene oxide dissolved in a nematic solvent
Authors: Degelaen J. , Arte E. , Dereppe J. M.
Published: February 2004

The generalized nuclear Overhauser effect evidenced by the INDOR technique has been used to analyze the PMR spectrum of ethylene oxide dissolved in a nematic phase solvent. This method allows the construction of the energy diagram of the spin system and an unambiguous determination of the sign of the direct coupling constants relative to the sign of the indirect coupling constants. Less common features such as double resonance on double quantum transitions and the repeated spacings effect were shown to be observable in nematic phases and to be useful in confirming the energy-level diagram.
ENDOR studies of the superhyperfine couplings of hydrogen-bonded protons. IV. Carboxyl radical anions in irradiated glycine and α-amino isobutyric acid
Authors: Iwasaki Machio , Muto Hachizo
Published: February 2004

The carboxyl radical anions trapped in irradiated single crystals of α-glycine and α-amino isobutyric acid have been studied by ENDOR. To elucidate the controlling factors for the selective proton transfer from the neighboring NH3 groups to the anion across the hydrogen bridge, the superhyperfine coupling tensors of the protons in the neighboring NH3 groups have been determined. The results suggest that two of the three amino protons hydrogen bonded to the COO group of the anion are located in the middle of the hydrogen bridge or jumping between the nitrogen and oxygen atoms. The latter interpretation seems to be more probable. The remaining one is located in the neighboring NH3 group. The following controlling factors suggested in our previous paper were confirmed by comparing the results with the reported crystallographic data: firstly, the protons participating in the hydrogen bond, which is formed in the direction of the unpaired electron orbital of the anion, are easily transferred to the anion side; and secondly, the hydrogen bond distance which is shorter than the others is favorable for the transfer.
Some anisotropy effects in molecular photoejection spectroscopy
Authors: Mukamel Shaul , Jortner Joshua
Published: February 2004

In this paper we present a theoretical study of the angular distribution of the fragments in the predissociation of diatomics. We have utilized scattering theory and the effective Hamiltonian approach to derive general expressions for the differential cross section and for the angular anistotropy under different excitation conditions.
Moments and distribution functions for polymer chains of finite length. II. Polymethylene chains
Authors: Yoon D. Y. , Flory P. J.
Published: February 2004

Statistical mechanical averages of vectors and tensors characterizing the configurations of polymethylene chains with n = 5–200 bonds have been calculated, these quantities being expressed in the internal reference frame attached to the first two bonds. Specifically, the persistence vector a ≡ 〈r〉 and the averaged center-of-mass vector 〈g〉 have been obtained as functions of chain length. They are compared to the corresponding vectors for various model chains. Configurational averages of the Cartesian tensors formed from ρ = r − a have been computed up to and including the tensor of seventh rank. Density distribution functions Wa(ρ), evaluated from these moment tensors using the three-dimensional Hermite series elaborated in the preceding paper, are approximately cyclindrically symmetric about a principal axis that lies close to the direction of a. The second moment (and, hence, the dispersion) along this axis is smaller than the moments perpendicular thereto. Acentricity and skewness of the distribution Wa(ρ) is large for n < 40 bonds; they are appreciable even at n = 100 bonds. For n ≥ 50, moments of the normalized density distribution can be represented in good approximation by a model chain consisting of freely jointed segments originating at the terminus of a, with each segment taken to be equivalent to 20 bonds of the real chain. The traditional approximation of the unnormalized density distribution about r = 0 by a freely jointed equivalent chain is subject to much greater error. The second moment tensor of gyration, averaged over all configurations, is approximately cylindrically symmetric, but its component (and its dispersion) along the symmetry axis is greater than in the transverse directions. This tensor is contrasted with that obtained by summing moments along the principal axes for individual configurations.
Ab initio study of the X2Π and A2Σ+ states of OH. I. Potential curves and properties
Authors: Chu Shih-I , Yoshimine M. , Liu B.
Published: February 2004

Accurate ab initio CI potential curves and molecular properties are presented for the X2Π and A2Σ+ states of OH. Results with known experimental values in parentheses are Re(X2Π) = 1.841(1.834) bohr, Re(A2Σ+) = 1.906(1.913) bohr, De(X2Π) = 4.43(4.63) eV, De(A2Σ+) = 2.29(2.53) eV, μ(OH,X2Π,ν=0) = 1.634(1.668) D, and μ(OD,A2Σ+,ν=0) = 1.861(1.72±0.10) D. Spectroscopic constants calculated from the theoretical potential curves are in satisfactory agreement with experimental results. Other molecular properties studied include quadrupole moments and the electric field gradient at the nuclei.
Semiclassical extension of Levinson's theorem to a particle interacting with a harmonic oscillator
Authors: Lin Ying-Wei , George Thomas F.
Published: February 2004

A semiclassical extension of Levinson's theorem to a model three-body system is presented. The system chosen is a particle interacting with a harmonic oscillator for collinear configurations. The theorem predicts the number N of three-body bound states that a potential energy surface can support, and this number is calculated for a set of surfaces for this model collinear system. The calculation involves the extrapolation of the S matrix to zero collision energy, where S matrix elements needed in the extrapolation are found in the classical limit. For comparison, N is also calculated in a purely classical fashion from the multidimensional phase space volume integral. The results from the semiclassical and purely classical calculations are in fairly good agreement.
Rate coefficients for oxidation of Ti+ and Th+ by O2 and NO at low energies
Authors: Johnsen Rainer , Castell F. R. , Biondi Manfred A.
Published: February 2004

Rate coefficients have been determined in a drift tube-mass spectrometer apparatus for the oxidation reactions of Ti+ and Th+ ions in O2 and NO for ion mean energies ranging from thermal (300 K) to 5 eV. Formation of the first oxides of metal ions M+ in the reactions M+ + O2 (NO) → MO+ + O (N) is found to occur with rate coefficients close to the theoretical maximum values (i.e., the ``Langevin'' limit), except for Ti+ + NO, which proceeds more slowly. Further oxidation in the reactions MO++O2 (NO)→ MO2++ O(N) has been detected only for M = Th and with small rate coefficients. The associative ionization reaction Th + O2→ ThO2+ + e has been observed to occur, although no rate coefficient can be obtained from our measurements. In addition, thermal energy ionic mobilities of thorium and titanium ions in helium are found to be μ0(Ti+) = (25.5±1) and μ0(Th+) = (15.75±0.5) cm2 V−1·sec−1 at 300 K.
Elastic properties of the nematic phase influenced by molecular properties
Authors: Gruler Hans
Published: February 2004

The intrinsic splay, twist, and bend deformations of nematic molecules are discussed. The intrinsic twist deformation leads to the cholesteric phase. On this molecular basis, the helical twisting power of cholesteric mixtures is discussed. The intrinsic splay and bend deformation cannot induce spontaneous deformation of a nematic liquid crystal but do influence the splay and bend elastic constants. Analogy is made between the change of the elastic constants and the electric orientation polarization produced by an electric dipole. The frequency dependence of the elastic constants is therefore similar to those of a dipole in a nematic surrounding. The splay elastic constant k11 has a low frequency relaxation (kHz-MHz), and the bend elastic constant k33 has a high frequency relaxation (MHz-GHz). The change of the elastic constants can be estimated for a realistic nematic molecule to be 10−6 dyn. The elastic constants can be described by two terms. The first one has some relation to the elasticity of ideal metals and the second one to rubber where the elasticity is controlled by the entropy.
Classical S-matrix calculation for vibrationally inelastic transitions in three dimensional collisions of Li+ with H2
Authors: Raczkowski Andrew W. , Miller William H.
Published: February 2004

The ``partially averaged'' version of classical S-matrix theory is applied to three dimensional collisions of Li+ with H2. For an initial collision energy of 0.684 eV cross sections for the vibrational deactivation of H2 from the initial state (n1,j1) = (1, 0) to final states (n2,j2), n2 = 0, j2 = 0, 2, 4,... are computed and compared with the recent quantum mechanical coupled channel calculations of Schaefer and Lester. The agreement is quite good, indicating that this approach is an accurate and practical way of describing these weak, ``classically forbidden'' processes which cannot be treated by ordinary classical trajectory methods.
Vibrational deactivation of carbon monoxide by hydrogen and nitrogen from 100 to 650 °K
Authors: Starr D. F. , Hancock J. K. , Green W. H.
Published: February 2004

Collisional quenching of carbon monoxide by hydrogen and nitrogen has been studied in the 100–650°K temperature range using the laser excited vibrational fluorescence method. The rate constant for CO–H2 deactivation increases smoothly with temperature from 2.6±0.3 sec−1·Torr−1 at 112°K to 170±15 sec−1·Torr−1 at 623°K. The vibration-to-vibration energy transfer results for CO–N2 mixtures (exothermic direction) show only a slight temperature dependence from 103 to 651°K with a broad maximum of 420±30 sec−1·Torr−1 in the temperature range 300–400°K. Comparison of our rates with high temperature shock tubes results show excellent agreement for the CO–H2 V → R,T process and only fair agreement for the CO–N2 V → V exchange process. This latter discrepancy may be partially due to the uncertainties involved in extracting V → V energy transfer rates from shock tube data.
Effect of changes in the potential on atom-solid elastic scattering
Authors: Wolken George
Published: February 2004

The relative intensity appearing in various diffraction peaks for the elastic scattering of an atom from a solid surface is studied as aspects of the interaction potential are varied. It is observed that the detailed relationship between the flat portion of the potential V0(z) and the (x,y)-dependent part on the repulsive wall (in the general region of the classical turning point) most strongly affects the diffraction properties. The scattering is relatively insensitive to the long range behavior of the flat part of the potential V0(z) and the long range behavior of the (x,y)-dependent parts.
Far infrared optical phonons of some two-dimensional layer compounds
Authors: Stoelinga J. H. M. , Wyder P.
Published: February 2004

The far infrared transmission spectra of the layer structure compounds of the type (CnH2n+1NH3)2 MCl4, n = 1,2,3, ···, (M=Cu, Cd) have been measured in the region of 10–400 cm−1 at 1.2 K. The rather involved spectra of all the compounds investigated can be interpreted in terms of the normal lattice modes of the layers alone. From these far infrared data, the contribution of the optical phonons to the specific heat has been estimated. A comparison with the result for this contribution obtained by Bloembergen, Tan, Lefevre, and Bleyendaal [J. Phys. (Paris) Suppl. 32, 874 (1971)] from a fit of the measured total specific heat leads to the conclusion that the absorption lines that we observed at wavenumbers lower than ∼40 cm−1 are probably due to multiphonon processes.
Study of the structure of molecular complexes. VI. Dimers and small clusters of water molecules in the Hartree-Fock approximation
Authors: Kistenmacher H. , Lie G. C. , Popkie H. , Clementi E.
Published: February 2004

The analytical fit to a large number of Hartree-Fock computations for the water-water interaction has been reanalyzed and used to study small clusters of water molecules. With the analytically fitted Hartree-Fock potential, thousands of possible configurations for the dimers, trimers, tetramers, pentamers, hexamers, heptamers, and octamers of water have been compared in order to determine the configuration of lowest energy (maximal stabilization energy). For the dimer two possible stable configurations are found, corresponding to an open form and a cyclic form, with the open form being more stable. For the trimers and tetramers the cyclic forms are somewhat more stable than the open structures. For the larger clusters it is concluded that it is rather meaningless to consider a single structure, but what is physically relevant is the statistical distribution of different configurations, since many configurations with significantly different geometry have nearly the same energy. The comparison of the stabilization energy per molecule of the different clusters with the corresponding value for liquid water does not support the mixture-model theories of the structure of liquid water.
Statistical mechanics of polar systems: Dielectric constant for dipolar fluids
Authors: Ho/ye J. S. , Stell G.
Published: February 2004

The Hemmer-Lebowitz-Stell-Baer formalism is used to derive an exact expression for the dielectric constant ε of a polar (nonpolarizable) system. The Kac inverse-range parameter γ is then introduced into the dipole-dipole potential, and it is shown that in a ``mean-field'' limit γ→0, the Clausius-Mosotti expression is recovered in the same way that a van der Waals-like theory has been previously recovered for simple fluids, a Debye-Hückel-like theory has been obtained for ionic fluids and the Weiss and Bragg-Williams theories have been recovered for lattice systems. In this limit the zero-field free energy reduces to the free energy of the same system at zero dipole moment. The relation this work bears to other formalisms and developments is discussed. In particular we show that our general expression and quite different-looking earlier expressions give the same ε. We have avoided the approximations made in earlier treatments by Nienhuis and Deutch and by Ramshaw, and our work helps to clarify the status of those treatments.
Photoelectron spectroscopy of high temperature vapors. V. HeI spectra of GaX3 and InX3 (X = Cl, Br, I)
Authors: Dehmer J. L. , Berkowitz J. , Cusachs L. C. , Aldrich H. S.
Published: February 2004

The HeI (584 Å) photoelectron spectra of GaX3 and InX3 (X=Cl, Br, I) are reported. All peaks are classified and the results are compared with spectra of the boron trihalides to bring out systematic variations caused by substituting different halogens and central atoms. A revision of the classification of the outermost e′ and e″ peaks in the spectra of BBr3 and BI3 is suggested. The spectra of GaI3 and InI3 exhibit splitting of the band due to ionization from an e″ MO (in D3h symmetry), which suggests that either the neutral ground state or the first excited 2E″ state of the ion is pyramidal.
Time-resolved photoionization mass spectrometry. Unimolecular fragmentation of toluene ions near threshold.
Authors: Buttrill S. E.
Published: February 2004

A new technique, time resolved photoionization mass spectrometry, allows direct observation of the fragmentation of excited ions. The loss of a hydrogen atom from toluene ions is studied using photoionization wavelengths from 1053 to 1026 Å. Nonlinear least-squares fitting of the decay curves of the molecular ion show that only three discrete states are involved in the fragmentation. One state has a fragmentation rate which is fast (k≫2×104 s−1) on the time scale of the experiment while the other two have rates of 1.3±0.4 and 1.9±0.4 s−1. The present results are consistent with earlier electron impact studies. A careful analysis of previous metastable ion lifetime measurements shows that they do not constitute evidence for a continuous distribution of lifetimes as had earlier been claimed. Evidence presently available indicates that the internal energy distribution of ions formed by electron or photon impact is best described in terms of a relatively small number of discrete states rather than a continuous distribution.
Self-diffusion coefficients of oxygen ion in single crystals of MgO · n Al2O3 spinels
Authors: Ando Ken , Oishi Y.
Published: February 2004

Oxygen self-diffusion coefficients in single crystal spinels were determined for three compositions of MgO · Al2O3, MgO · 1.2Al2O3, and MgO · 2.2Al2O3 by a gas-solid exchange technique utilizing 18O as a tracer. The temperature dependence of the self-diffusion coefficient for MgO · Al2O3 was expressed as D = 0.89 exp(− 105 × 103/RT) cm2/sec. The self-diffusion coefficients for MgO · 1.2Al2O3 and MgO · 2.2Al2O3 were close to that for MgO · Al2O3, which was interpreted as being due to intrinsic diffusion. The determined self-diffusion coefficient of oxygen ion was smaller by several orders of magnitude than that of magnesium ion and was closer to the apparent diffusion coefficients calculated from the sintering rates. The influence of surface exchange reaction was noticed in determining the self-diffusion coefficient.
Reaction kinetics in stochastic models. II
Authors: Widom B.
Published: February 2004

Three distinct topics in the theory of stochastic models of chemical reaction kinetics are discussed. The first, treated in Sec. II, concerns the case of two or more simultaneous reactions, as typified by the mutual interconversion of three or more species. The formula that relates the rate constants to the microscopic transition rates is discussed. The same formula, alternatively interpreted, is then seen also to be the relation that one would use to derive experimental rate constants from the amplitudes and time constants that are the primary experimental data. The second topic is that treated in Sec. III, which is on a class of stochastic models for which the conventional steady-state approximation is essentially exact. The origins and implications of that circumstance are discussed. The third subject is that of Sec. IV, on a fundamental difference between three-center exchange reactions A+BC⇄AB+C and (bimolecular) isomerizations A⇄B. The difference is in certain dynamical features of the respective collision mechanisms, which in one case imply that an ``equilibrium'' approximation to the rate constant, such as that given by transition-state theory, would be a good approximation, and in the other case not.
Spin projection of single-determinant wavefunctions
Authors: Phillips Donald H. , Schug John C.
Published: February 2004

Using the method of expansion in terms of the natural orbitals of charge density, we have rederived the components of the one- and two-particle density matrices that result upon spin projection of a single-determinant wavefunction. We have corrected several errors in the unrestricted two-particle density matrix elements given by Harriman and co-workers, pointed out the necessity of correcting the phases of the natural orbitals, and generalized the theory to the extent necessary to treat molecules having unequal numbers of electrons and basis orbitals. The theory has been applied to several of the types of cases for which the use of the projected UHF method is desirable: (a) small hydrocarbon radicals and singly charged ions, (b) hydrocarbon ions with pseudodegenerate ground states, and (c) a postulated photoproduct of dipyridyl, which had previously been predicted to be a triplet. The UHF wavefunctions of several of the small hydrocarbon radicals and monoions have only limited spin contamination by higher multiplicity states and therefore provide good checks on the correctness and internal consistency of the present results by comparison with the results obtained by alternative methods. The results on the ions with pseudodegenerate ground states demonstrate that the projected UHF theory provides a good alternative to extensive configuration interaction treatments. The results for the postulated photoproduct of dipyridyl reverse the earlier prediction of the ground state multiplicity and demonstrate the importance of comparing energies of UHF wavefunctions for both the singlet and triplet states for predicting singlet-triplet splittings.
Dipole moment derivatives and infrared intensities. I. Polar tensors
Authors: Person Willis B. , Newton James H.
Published: February 2004

The analysis of infrared intensity data to obtain atomic ``polar tensors,'' introduced first by Biarge, Herranz, and Morcillo (1961), is reviewed and slightly reformulated to make it more consistent with nomenclature currently in use for normal coordinate calculations. Some properties of these polar tensors are examined, including their relation to the ``effective charges'' introduced by King, Mast, and Blanchette (1972). The procedure is illustrated for formaldehyde and for ethylene to obtain the polar tensors and effective charges for the H, C, and O atoms. A revised set of normal coordinates is used for the latter molecule. The results are compared and discussed.
Fluctuations and transitions at chemical instabilities: The analogy to phase transitions
Authors: Nitzan Abraham , Ortoleva Peter , Deutch John , Ross John
Published: February 2004

The properties of a reacting system near an instability are investigated and the analogy between transitions in unstable systems and equilibrium phase transitions is developed in detail. The set of macroscopic steady state rate equations plays the role of an equation of state. The bifurcation points of this set are analogous to transition and critical points of equilibrium phase transitions. Hard transitions of unstable systems correspond to first order and soft transitions to second and higher order phase transitions. Critical exponents are defined for those properties of the unstable systems which are singular at the transition points, and relations between these critical exponents are investigated. Critical fluctuations are studied with stochastic analogs of the macroscopic rate equations. Both master and Langevin equations are considered and lead to the following conclusions: When a transition or a critical point is approached (a) the amplitude of fluctuations grows; (b) the lifetime of these fluctuations becomes longer; and (c) the spatial correlation length increases. Our approximations are similar to those made in mean field theories of phase transitions and our results are thus ``classical.'' However the critical exponents are not necessarily numerically identical to the Landau-Ginzburg exponents since they depend on the particular nonlinear system.
Magnetic resonance line shapes in solids. III. Methyl group tunneling in low temperature glasses
Authors: Mottley Carolyn , Johnson Charles S.
Published: February 2004

NMR line shapes are reported for the protons in CH3CD2OD, CH3CD2Cl, CH3CD2Br, and CH3CD2I dissolved in perchloropropene glass at liquid helium temperature. Spectra were also observed for the solutions containing CH3CD2Br and CH3CD2I up to 120°K. All of the low temperature spectra are anomalous in shape and appear to result from superimposed spectra for methyl groups having different rotational barriers. An analysis is presented, based on the tunneling calculation of Apaydin and Clough, which yields two rotational barrier heights for each compound.
Cross sections for the alkali atom-Cl2 reactions
Authors: Maya J. , Davidovits P.
Published: February 2004

Total reaction cross sections for the alkali atoms with chlorine molecules have been obtained by direct measurement of alkali atom transient decay rates. The results are Na, 124 Å2; K, 154 Å2; Rb, 190Å2; and Cs, 196 Å2. These results are accurate to about 15%. The relative accuracy within the alkali atom sequence is about 5%. The results are compared with theoretical calculations.
Lowest triplet state of a simple merocyanine dye
Authors: Marchetti A. P. , Landry J. F. , Tinti D. S.
Published: February 2004

The lowest triplet state of 3-ethyl-5-(1,3-dithiolanylidene)-rhodanine has been studied in solution and in single crystals at liquid helium temperatures. This state is tentatively assigned as a ππ* state. The origin in single crystals is composed of two lines separated by 0.6 cm−1. These lines have been interpreted as the allowed Au and Bu factor-group states from Zeeman spectra. Optically detected magnetic resonance measurements of the isolated molecule yield values of 0.1289 and 0.02585 cm−1 for the zero-field parameters |D| and |E|, respectively.
Relative orientations of the 14N EFG tensors in hydrazine from pure nuclear quadrupole relaxation study
Authors: Vega Shimon
Published: February 2004

The description of the PNQR relaxation in the ν plane is extended to the case of two nuclei of spin I = 1 interchanging by a dynamic process. The theory is applied to hydrazine, in which the two inequivalent nitrogen atoms interchange sites. Spin lattice relaxation measurements on all six 14N NQR lines were done at 228°K. Three types of experiments were performed: (i) steady state continuous pulse experiments, (ii) two-pulse experiments on the same transitions, and (iii) cross relaxation experiments in which the first pulse was applied to a transition of one site and the second pulse to the corresponding transition of the other site. Detailed analysis of these experiments gave accurate results for the relative orientations of the EFG tensors of the two 14N sites. The angles between the corresponding directions are: φXX = 93°.7, φYY = 16°.7, and φZZ = 91°.0.
Radial distribution function for hard spheres from scaled particle theory, and an improved equation of state
Authors: Reiss H. , Casberg R. V.
Published: February 2004

Previous applications of scaled particle theory have been limited to the calculation of thermodynamic properties of fluids rather than structure. In the present paper, the theory is expanded so that it is capable of yielding the radial distribution function. The method is first illustrated by applying it to one- dimensional fluids of hard rods where, as in other theories, the radial distribution function is obtained exactly. It is then applied to a fluid of hard spheres where a closure condition is necessary. This condition is supported by recent work in scaled particle theory dealing with the thermodynamics of boundary layers. It is used to calculate the radial distribution function around a λ-cule of varying size, including one of the size of a typical hard sphere solvent molecule. The results are very good, yielding (at the highest density at which numerical solutions have been possible, ρ=0.372ρ0, where ρ0 is the density of close packing) results for the contact radial distribution function and the equation of state which were somewhat better than the original scaled particle and Percus-Yevick theories. These theories yield results which are very close to the predictions of Monte Carlo calculations. As in the original scaled particle theory directed at the contact distribution function alone, exact results (exact closure) are possible for λ-cules of radii corresponding to a point or smaller. Our numerical method becomes unstable for densities higher than ρ=0.372ρ0, and we are attempting to improve the procedure.
Rates of collision-induced emission from metastable O(1S) atoms
Authors: Cunningham D. L. , Clark K. C.
Published: February 2004

The radiative decay of metastable 1s22s22p4 1S0 atomic oxygen atoms has been shown to proceed at a rate depending linearly on the concentration of argon or xenon present in the gas mixture. With increasing pressure, the 1D2–1S0 atomic line at 5577 Å becomes accompanied by a broad emission region identified as a band system of a weakly bound rare-gas oxide molecule. Changes in the transition probability as a function of pressure were measured by using the spin-forbidden 3P1–1S0 transition at 2972 Å as a pressure-independent monitor of the O(1S) concentration. The observed pressure dependence of the emission probability may be described by rate constants for induced emission in argon and xenon atmospheres: (1) for emission in a bandwidth of ±1.6 Å centered on the atomic line at 5577 Å, k(Ar)=(7±3)×10−20 cm3 sec−1, k(Xe)=(3±2)×10−19 cm3 sec−1; and (2) for emission into the entire green band system, k(Ar)=(3.0±.2)×10−18 cm3 sec−1, k(Xe)=(1.7±.2)×10−15 cm3 sec−1. Comparison is made with rate constants for deactivation of these metastable atoms by the same rare gases. It appears that substantially all of the collision-induced emission comes from bound rare-gas oxide molecules whose dissociation equilibria provide the observed pressure dependence.
NMR study of the two-phase equilibrium in cysteine hydrochloride monohydrate. II
Authors: Knispel Roy R.
Published: February 2004

Cysteine hydrochloride monohydrate undergoes a phase transition at 333°K. The two-phase equilibrium existing above this transition temperature has been investigated by proton spin-lattice relaxation time measurements. In approaching the transition temperature of 333 °K from below, a molecular diffusion process (activation energy ≃24 kcal/mole) was detected from measurements of the dipolar spin-lattice relaxation time. Above 333°K, the laboratory spin-lattice relaxation is nonexponential and over the temperature range of the measurements (333° to 390°K) may be described by two relaxation times. The frequency dependence of the spin-lattice relaxation was measured at 338° and 351°K and both spin-lattice relaxation times were found to be frequency independent, suggesting that in each component T1 is determined by a fast process, i.e., τc ≪ 2×10−8 sec.
ENDOR characterization of the free radical in irradiated thymidine
Authors: Box Harold C. , Budzinski Edwin E. , Potter William R.
Published: February 2004

The stable free radical produced by ionizing radiation in the nucleoside thymidine has been studied by ENDOR spectroscopy. The radical is formed by addition of hydrogen to the C6 carbon atom of the thymine ring. The hyperfine couplings of the CH2 protons and the methyl group rotational splitting constant are deduced from ENDOR measurements at 4.2°K.
Statistical derivation of similar form to the Mooney-Rivlin expression for unswollen elastomers
Authors: Tatara Yoichi
Published: February 2004

The Mooney-Rivlin C2 term has not been based on any network structure. An affine deformation expressed as ratios (1/αx, 1/αy, 1/αz), where αx, αy, αz are the ratios of macroscopic dimensions to those for the undeformed specimen, is presented for changes in the vectorial lengths of some chains of a network involved in simple elongation, in considerations of network connectivity, and in some conditions regarding the directions of chain vectors at junction points. One expression for stored elastic free energy in unswollen rubber elastic bodies is statistically derived from the above affine deformation assumption. The derived expression is similar in form to the Mooney-Rivlin term. A relation between C1(entropy) and C2(entropy) is developed. It is inferred that hysteresis will involve the increase in C2(entropy) or the C2 term derived here. Some results in this paper are confirmed in light of several previous and present experimental results.
On the evaluation of kinetic theory collision integrals. II. Angular momentum coupling schemes
Authors: Hunter L. W. , Snider R. F.
Published: February 2004

The collision integrals of the Waldmann-Snider collision superoperator are expressed in terms of three different rotationally invariant matrix representations of the transition operator. Two of these forms were first introduced by Curtiss and involve a translational-internal coupling scheme of angular momenta, while the third form is the standard total angular momentum representation. The expressions for the collision integrals in one of the Curtiss forms are valid for nonvibrating diamagnetic diatomic molecules, while the other expressions are valid for diamagnetic polyatomic molecules.
Improved solutions to the equation of motion in the uniform WKB theory for two-channel problems
Authors: Cho Ung-In , Eu Byung Chan
Published: February 2004

The equation of motion in the uniform WKB theory for a two-channel problem is reinvestigated in order to obtain improved approximate solutions that would perform better than the first order Magnus approximation solution previously used in the analysis of two-channel inelastic collision problems. We have developed two approximate solutions and investigated their variants in the paper. The two main improved approximate solutions are obtained by properly resumming the Magnus expansion in a novel way and also by appropriately modifying the equation of motion such that the Magnus approximation used on it would not damage the accuracy of the solution thus obtained. The solutions obtained give rise to transition probabilities well comparable over a wide range of the coupling constant with those obtained by the numerical solution of the coupled Schrödinger equations.
Thermochemistry and energy partitioning in the charge separation reactions of doubly charged triatomic ions
Authors: Cooks R. G. , Terwilliger D. T. , Beynon J. H.
Published: February 2004

Ion kinetic energy and appearance potential measurements have been used to study the unimolecular charge separation reactions of the triatomic ions CO22+, COS2+, CS22+, N2O2+, NO22+ ·, and SO22+. The experimentally determined metastable peak shapes have been compared with calculated peak shapes including calculations that determine both the average kinetic energy release and the distribution about this average. The product ion states have been assigned from the thermochemical data, and in all the reactions total spin and angular momentum are found to be conserved. There is evidence that the metastable peaks are associated with maxima on single potential surfaces rather than with a slow predissociation. For CO2++ and COS++ almost all the available energy is partitioned into translational energy of product separation.
Semiclassical treatment of vibrational-translational energy transfer in the near-adiabatic approximation
Authors: Cady W. A.
Published: February 2004

Vibrational-translational energy transfer is examined in the near-adiabatic (or perturbed stationary states) approximation by treating the relative motion classically. The value of this approach is demonstrated by comparing the results obtained here with the exact results as well as with the results of other approximate treatments. The regions of validity of the approximation employed are discussed and are shown to be essentially the same as those indicated by the totally classical treatment of Attermeyer and Marcus. Best results are obtained for the lower energy, less impulsive collisions. An analytic expression is derived to permit quite accurate results to be calculated quickly and easily.
Mass spectrometric studies of gaseous ThO and ThO2
Authors: Hildenbrand D. L. , Murad Edmond
Published: February 2004

High temperature mass spectrometric techniques have been used to study the equilibria (1/2)Th(s)+(1/2)ThO2(s)=ThO(g), (1); ThO(g)+Si(g)=Th(g)+SiO(g), (2); Th(g)+ThO2(g)=2 ThO(g), (3). From the equilibrium data and related electron impact measurements the following quantities have been derived: Δ fH(ThO,g,298.15 K) =−4.6±5.9 kJ/mol; D0° (ThO)=848± 13 kJ/mol (or 8.78 ±0.13 eV); IP(ThO) ≥6.0 eV; Δ fH(ThO2,g, 298.15 K)=−443±25 kJ/mol; D0°(ThO2)1532± 30 kJ/mol (or 15.9±0.3 eV); and IP(ThO2)=8±1 eV. A second-law analysis of Reaction (1) gives a measure of the magnitude of the electronic partition function of ThO. Difficulties in interpreting the ThO ionization threshold are described. The relationship of these measurements to recent kinetic studies is briefly discussed.
Low-energy electron impact study of acetone
Authors: St. John Willard M. , Estler Ron C. , Doering John P.
Published: February 2004

A low-energy, high resolution, electron impact spectrometer with a molecular beam target has been constructed and used to study the electronic energy levels of acetone vapor. Similar spectra were also taken with a second electron spectrometer having a static gas target. Both sets of spectra are essentially identical and show the expected singlet states at 4.37, 6.35, and 7.45 eV, the first triplet state at 4.16 eV, and a very broad second triplet process from 5.3 to 6.1 eV with an intensity maximum at 5.88 eV. Attempts to resolve vibrational structure in the latter band were unsuccessful, even though vibrational spacings of 0.14 eV were easily resolved elsewhere in the spectrum.
Effect of an external electric field on the yield of free ions. III. Electron scavenging at small concentrations
Authors: Mozumder A.
Published: February 2004

The method of prescribed diffusion has been applied to obtain the evolution of the neutralization process of an ion pair in the presence of an external electric field. For relatively small external fields the probability of escape calculated by this method agrees exactly with the Onsager formula. The probability of the existence of the ion pair against neutralization has been evaluated in the long-time limit and its Laplace transform determined to give the scavenging probability in the presence of an external field E at small concentrations. Analysis of the results shows that, at small concentrations, the yield of the scavenging reaction should vary with scavenger concentration c as (c + c0E2)1/2, where c0 is some constant, rather than simply as c1/2. Replotting of the experimental data of Rzad and Bakale according to the present procedure removes the discrepancy between their extrapolated yield at zero concentration and the results of the Onsager theory. The maximum and minimum scavenger concentrations within which a square root variation of yield with concentration is to be expected are evaluated as functions of the external field.
Degenerate perturbation theory
Authors: Klein D. J.
Published: February 2004

A number of different perturbation formulations found in the literature are discussed. Although these formulations are derived in quite different ways, simple relations among these derivations are described and, in fact, some are shown to yield identical results. One of these degenerate perturbation theories resulting from different formulations due to Van Vleck, Kemble, and Primas, to des Cloizeaux, and to Buleavski is considered in greater detail. Its linked and cluster expansion properties and some other resummation techniques are briefly discussed.
Intramolecular energy transfer in cis-trans isomerization: A study of fluorescence from single vibronic levels of styrene, trans-β-styrene-d1, styrene-d8, and ethynlbenzene
Authors: Hui Man Him , Rice Stuart A.
Published: February 2004

The fluorescence lifetimes of, and quantum yields of emission from, individual vibronic levels of isolated molecules of styrene, trans-β-styrene-d1, styrene-d8, and ethynlbenzene have been measured. These data are subjected to a decomposition, under a plausible hypothesis, into parameters descriptive of an isomerization process and an intersystem crossing process. It is argued that the two processes proceed independently in parallel. The rate of isomerization is found to be independent of the vibrational energy content of the isolated molecule and to have a dependence on isotopic mass consistent with the prediction that the torsional mode is the best ground state acceptor in the reaction channel. A plausible schematic potential energy surface is constructed from a combination of spectroscopic observations and analogies with theoretically derived surfaces for similar molecules. Analysis of the experimental data, and deductions from those data, in terms of the properties of the potential surface, leads to the inference that intramolecular vibrational relaxation is slower than chemical reaction for excess vibrational energy up to ∼2500 cm−1.
ESR study of trapped electrons produced in alkane glasses at 4 °K
Authors: Hase Hirotomo , Warashina Tetsuo , Ogasawara Masaaki , Higashimura Takenobu
Published: February 2004

In gamma irradiated 3-MP, MCH, and 3-MHX glasses, the same et− yields were obtained between 4 and 71°K, indicating that electrons are stabilized in pre-existing traps prior to solvation. The linewidths were reduced on warm-up of the glasses irradiated at 4°K and depended on the annealing time at 71°K, implying that the solvation occurs very slowly around 71°K. A comparative study of power saturation in 3-MP and MCH suggested that the spurs formed at 4°K were spatially expanded compared to those at 71°K. The structural change of trapping sites caused by solvation was clearly reflected on the power saturation characteristics.
Rotational relaxation in polar gases
Authors: Agrawal P. M. , Saksena M. P.
Published: February 2004

An expression for transition probability for rotational-translational energy transfer for polar molecules has been derived, using the distorted wave approximation. The polar molecules have been assumed as point dipoles imbedded in hard cores. Calculations have been performed for the transition (1 → 0, 1 → 0) for HCl, DCl, HBr, H2O, H2S, and NH3 at various temperatures (300–500 °K). The calculated (Zrot)10 values are in good agreement with experimental (Zrot)eff data. Further, the theory predicts decrease of (Zrot)10 with increase in temperature, dipole moment, and moment of inertia. The temperature dependence is thus opposite to that predicted by the classical theory of Zeleznik, but agrees well with the dependence of (Zrot)eff obtained from experimental thermal conductivity data.
Optical properties of some aromatic liquids in the vacuum ultraviolet
Authors: MacRae R. A. , Williams M. W. , Arakawa E. T.
Published: February 2004

The optical properties of benzene, pyridine, quinoline, and 2-ethylnaphthalene in the liquid state have been studied for photon energies from 2 to 10.6 eV. For each liquid the extinction coefficient k has been obtained from transmission measurements, and self-consistent values of the refractive index n calculated over the experimental energy range by a Kramers-Kronig analysis. The calculated absorption cross sections per liquid molecule have been compared with the corresponding absorption cross sections per vapor molecule, where the vapor data have been obtained from the literature. The absorption cross section spectra for liquid and vapor are very similar in the energy region studied, such that the observed absorption can be attributed to the same electronic excitations in both phases. In addition, evidence of collective excitations of electrons, not seen in the vapor state, is seen in all four liquids.
Use of rotation operators in the general description of polymer properties
Authors: McBrierty Vincent J.
Published: February 2004

In this paper we are concerned with the formulation of a general mathematical scheme which may be used to describe many polymer properties of interest. The responses of polymers to the following experimental techniques have been analysed: infrared absorption, x-ray diffraction, nuclear magnetic resonance absorption, fluorescence polarization, and elasticity measurements. A principal feature of the analysis is the use of matrix elements of the three-dimensional rotation operator. This approach greatly facilitates the treatment of the various types of symmetry, both statistical and crystallographic, which are often an inherent feature of polymer structure. It is clearly demonstrated how measurements from different experiments can complement each other and lead to a more complete description of the polymer.
Dielectric constant of ice
Authors: Nagle J. F.
Published: February 2004

A series expansion for the dielectric constant of the Bernal-Fowler-Pauling model of ice relaxed to allow Bjerrum faults is developed using a renormalization technique which eliminates large numbers of subgraphs. In the no fault limit the dielectric constant has the form ε0 = ε∞ + (4πG/3)(N/V)(μ2/kT) where the Bethe type approximation yields G = 3 and the exact result in two dimensions is G = 9/π. In two dimensions the series for G exhibits reasonable convergence to the exact result. For cubic ice the series of Gobush and Hoeve are confirmed and slightly extended. These cases lend support to the series results for the Bernal-Fowler-Pauling model of hexagonal ice; namely, that there is very little anisotropy in ε0 and G is very close to 3. These results are used in discussing whether more refined models of ice are needed. Also, the discussion comparing G with the Kirkwood correlation function gK, begun by Stillinger and Cotter, is continued.
Kinetics of immobilized multienzyme systems
Authors: Ho S. P. , Kostin M. D.
Published: February 2004

Expressions are derived for the concentration of the end product of an immobilized multienzyme system in which consecutive reactions and diffusion occur. The analysis is carried out for both steady-state and transient conditions. The final results show explicitly how the concentration of the end product depends on the diffusion coefficient, the number of enzymic reactions, the rate constants, and other parameters of the system.
Polypeptide liquid crystals: Magnetic susceptibility, twist elastic constant, rotational viscosity coefficient, and poly-γ-benzyl-L-glutamate sidechain conformation
Authors: Sridhar C. Guha , Hines W. A. , Samulski E. T.
Published: February 2004

The bulk magnetic susceptibilities of several synthetic polypeptides have been measured. The observed anisotropy of the diamagnetic susceptibility Δχ for oriented nematic liquid crystals of poly-γ-benzyl-L-glutamate (PBLG) in dichloromethane is 7.0±0.7×10−6 emu/mole. For a PBLG axial ratio of 150, a value of the twist elastic constant K22=273×10−7 emu cgs is calculated by measuring the critical magnetic field for untwisting the cholesteric supra molecular structure in the liquid crystal. The rate of reorientation of the nematic director of an aligned nematic PBLG structure yields a value for the rotational viscosity coefficient, γ1=2.8×105 P. K22 and γ1 appear to be sensitive to the polypeptide axial ratio and solvent composition. The possibility of extracting polypeptide sidechain structural information from Δχ measurements in the liquid crystal is discussed.
Deuteron magnetic resonance study of the antiferroelectric phase of ND4D2PO4
Authors: Blinc R. , Slak J. , Zupančič I.
Published: February 2004

The O–D ⋯ O deuteron quadrupole coupling tensors have been determined in the antiferroelectric phase of ND4D2PO4. The results show that the antiferroelectric phase transition in ND4D2PO4 is connected with an order-disorder transition of the deuterons in the O–D ⋯ O bonds and that the Nagamiya model of hydrogen ordering is correct.