bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic relaxation of quadrupolar nuclei in nonaqueous electrolyte solutions
Authors: Melendres C. A. , Hertz H. G.
Published: February 2004

The NMR relaxation times of the quadrupolar nuclei 7Li, 23Na, 87Rb, and 133Cs in electrolyte solutions in methanol have been measured with pulse and wide-line techniques. In addition, 87Rb relaxation rates were obtained in solutions of RbF in ethanol, ethylene glycol, and formamide. The data were used to test an electrostatic relaxation theory in the limit of infinite dilution. The theory furnished the relaxation rates of the correct order of magnitude when the suitable model for the state of solvation is applied. With measurements on the concentration dependence of the relaxation rates, the electrostatic theory also allows calculation of the contribution to the relaxation rate due to ion-ion interaction.
Neutron irradiation effects and structure of noncrystalline SiO2
Authors: Bates J. B. , Hendricks R. W. , Shaffer L. B.
Published: February 2004

The nature of the defects produced in noncrystalline SiO2 and α-quartz single crystals by fast neutron irradiation (E > 0.18 MeV) has been investigated by Raman and infrared spectroscopy, small-angle x-ray scattering, and electron microscopy. Measurements were made at 25°C on samples irradiated to integrated fluxes (exposures) from ∼1×1018 to 2×1020 neutrons/cm2 (n/cm2). It was observed that at 2×1020 n/cm2, the α-quartz sample had been transformed to an essentially noncrystalline material. However, at 9×1019 n/cm2, remnant crystallites of the original α-quartz having a radius of gyration of 47 Å were found. The spectra of the noncrystalline phase of these materials are interpreted in terms of local modes at defect centers. Simple models are considered which account for the vibrational spectra and extrapolated x-ray scattering in the forward direction. The post-irradiation annealing behavior of the α-quartz samples has been followed to 1000°C. It was found that the structure of the noncrystalline phase gradually transformed to that of unirradiated SiO2. In the α-quartz sample irradiated to 9×1019 n/cm2, the remnant microcrystallites were found to anneal out by 1000°C.
Optical and dielectric properties of DNA in the extreme ultraviolet
Authors: Inagaki T. , Hamm R. N. , Arakawa E. T. , Painter L. R.
Published: February 2004

Optical constants of dry films of deoxyribonucleic acid (sodium salt of calf thymus DNA) have been determined in the 2–82 eV region of photon energy. The extinction coefficient k was obtained by transmission measurements on thin films on metal mesh screens. The refractive index n in the nonabsorbing region 2–4 eV was obtained from critical-angle measurements on films deposited on a sapphire semicylinder. To determine the value of n above 4 eV, a Kramers-Kronig analysis was performed using the measured values of k. From these optical constants the complex dielectric function ε and the energy-loss function for charged particles −Im(1/ε) were derived. The results exhibit, in addition to the well-established absorptions around 4.7 and 6.5 eV, a strong absorption at 13.8 eV and a prominent peak in the energy-loss function at 21.6 eV which exhibits a large degree of collective behavior.
Water trimer decay rate
Authors: Hagen Donald E. , Kassner James L.
Published: February 2004

A molecular model is used to study the problem of time dependent bond breaking in a simple cluster system, the water trimer. The intermolecular vibrations of the cluster are broken down into normal modes. A cluster decay rate is calculated based on the rate at which the normal modes combine constructively to strain a bond to the breaking point. Strain energies arising from bond stretching and bond bending are included. The model can be extended to larger cluster sizes and offers an alternative technique to the classical approach for arriving at the kinetics of cluster growth.
Semiclassical calculation of bound states of a multidimensional system
Authors: Eastes Walter , Marcus R. A.
Published: February 2004

The semiclassical quantum conditions for bound states are studied for a nonseparable system of two coupled oscillators which possesses a collection of quasiperiodic trajectories. The semiclassical energy levels are found to be in excellent agreement with the exact quantum levels. This treatment differs from previous work in that periodic trajectories are not needed and in that the potential surface is smooth and nonseparable in all regions.
Carbon-13 hyperfine splittings of normal and abnormal methyl radicals trapped on the porous Vycor glass surface
Authors: Fujita Yuzaburo , Katsu Takashi , Sato Mitsuo , Takahashi Kazumasa
Published: February 2004

To clarify the electronic structure and motional state of the abnormal methyl radical, we studied the 13C-hf splittings of normal and abnormal methyl radicals photoproduced and stabilized on the surface of porous Vycor glass, as well as that of the methyl radical-iodide ion adduct prepared by γ-irradiation of 13CH3I in a CD3CN matrix at 77 K. The ESR spectra of all the methyl radicals quoted above exhibited axially symmetric features with respect to the 13C-hf (and 127I-hf) tensors at low temperatures. A significant decrease in the isotropic 13C-hf constant of the abnormal methyl radical compared with that of the normal one is interpreted in terms of the spin-delocalization onto the oxygen atom of the surface siloxane bridge, keeping its structure planar. The fact that the 13C-hf tensors of all the methyl radicals show a trend of A∥ (13C) > A⊥ (13C) implies that the normal and abnormal methyl radicals interact with the surface via the 2pπ unpaired-spin orbital and rotate around the C3 axis. The temperature dependence of the isotropic 13C-hf splitting of the normal methyl radical was also reexamined in the temperature range 77–300 K, and, accordingly, the result was found to agree well with the theoretical calculation by Schrader based on the extra coupling due to the out-of-plane vibration.
Exactly solvable model for nonradiative decay with variable coupling strength
Authors: Morokuma Keiji , Freed Karl F.
Published: February 2004

We introduce an exactly solvable model for radiationless decay which involves a single discrete level which is coupled to a quasicontinuum with a variable strength that qualitatively mimics that produced by a Franck-Condon factor. Explicit solutions are presented for the large molecule statistical limit as illustrations of the use of the model. It is shown that the statistical limit of this model produces behavior indicative of the intermediate case, e.g., nonexponential decays and quantum beats, and the physical origin of these effects is discussed.
Reactions of ions in excited electronic states: (N2+·)* + N2 → N3++N
Authors: Bowers Michael T. , Kemper Paul R. , Laudenslager James B.
Published: February 2004

The formation of N3+ ions from N2+· ions in an excited electronic state has been studied using ion cyclotron resonance (ICR) spectroscopy. By analysis of the ICR data is was possible to determine the rate constant for formation of N3+ to be k3 = 5.5±1.0×10−11 cm3 sec−1·molecule−1, the lifetime of the precursor N2+· excited state to be 1/k4>10−2 sec, and the ratio of active N2+· excited states to the remainder of the N2+· formed in the electron beam to be k2/k1 = 10±1×10−3. Comparison with previously published single source work and with optical studies of Holland and Maier indicate that at least two excited states of N2+· may be responsible for the formation of N3+ in the single source instruments, the A 2Π state (τ ≃ 6×10−6 sec) and a quartet state (τ ≥ 10−2 sec). The onset of N3+ formation in the ICR is at 22.6±0.6 eV, about 1.5 eV above the onset in the single source mass spectrometer. It is suggested the ICR onset corresponds to the onset of the active quartet state and the mass spectrometer onset to the thermodynamical onset of the N3+ ion. This analysis yields Δ Hf (N3+)=372± 4  kcal/mole.
Theory of the angular distribution of molecular photofragments
Authors: Yang Sze-cheng , Bersohn Richard
Published: February 2004

The theory of the anisotropy of the flux of molecular fragments produced by polarized light has been discussed previously for linear molecules by Zare, Jonah, and Busch and by Wilson but is here analyzed more systematically for an arbitrary molecule. Polarized light creates a cosine squared distribution of excited molecules and the distribution of fragments is given by f(θ) = (1/4π)[1 + βP2(θ)], where θ is the angle between the detection direction and the electric vector of the light. The parameter β depends on the orientation in the molecular framework of the transition dipole moment and the dissociation direction and on the time averaged correlation functions 〈 〈 Dm m′(2) [δ Ω (t)]〉 〉 of the rotating molecules. The correlation functions can be evaluated exactly for linear and spherical top molecules and can be expressed in terms of one dimensional integrals for symmetric tops using the techniques of St. Pierre and Steele. Correlation functions for asymmetric tops have not yet been evaluated. These correlation functions are not only averages over the Boltzmann distribution of rotational energies of the molecules, but they are also averages over the distribution of lifetimes of the excited state. Thus the anisotropy β emerges as a rather complex quantity but numerous formulae for β are given which apply to special cases of practical interest.
Photodissociation of molecular beams of aryl halides
Authors: Dzvonik M. , Yang S. , Bersohn R.
Published: February 2004

A molecular beam photodissociation study has been made of a number of simple aryl iodides and bromides. The angular distribution of photofragments is characterized by an anisotropy parameter β which was measured for each molecule. The values of β depend on the lifetime of the excited state compared to the rotational correlation times of the molecule as well as on the orientation of the transition dipole with respect to the C–X bond. Knowing these orientations we can extract excited state liftimes as follows: methyl iodide, 0.07 picoseconds (psec); iodobenzene, 0.5 psec; α-iodonaphthalene, 0.9 psec; and 4-iodobiphenyl, 0.6 psec. It is concluded that methyl iodide directly dissociates but that the aryl compounds predissociate. The analogous aryl bromides have small anisotropy parameters and it is estimated that they live in the excited state perhaps two orders of magnitude longer than the aryl iodides. The data suggest a mechanism for predissociation in which S2 undergoes intersystem crossing to a triplet state localized on the C–I bond either directly or via S1.
Merging beams study of the H2+(H2,H)H3+, H2+(D2,H)HD2+, and D2+(H2,H)HD2+ reaction mechanisms
Authors: Lees A. B. , Rol P. K.
Published: February 2004

A merging beams apparatus was used to measure energy distributions of ions formed in the H2+(H2,H)H3+ reaction for collisions with relative energy W in the range 0.1 eV≤W≤10.0 eV. The major components of the reaction, proton and hydrogen atom transfer, were resolved through study of the H2+(D2,H)HD2+ and D2+(H2,H)HD2+ reactions, respectively. Each component follows predominantly direct interactions at all energies studied and contributes nearly equally to the H2+(H2,H)H3+ reaction for W≤6 eV. At higher energies, hydrogen atom transfer becomes increasingly more important; the final relative energy W′ agrees qualitatively with the abandoned atom model. The growth of a satellite peak for W > 7 eV indicates the appearance of an electronically excited product.
Product state analysis of BaO from the reactions Ba + CO2 and Ba + O2
Authors: Dagdigian P. J. , Cruse H. W. , Schultz A. , Zare R. N.
Published: February 2004

The reactions Ba + O2 → BaO + O and Ba + CO2 → BaO + CO have been investigated using the method of laser-induced fluorescence to detect the BaO products. Excitation spectra of BaO produced under single-collision conditions in these reactions are reported, and initial rotational population distributions for BaO formed in the v=0 vibrational level are deduced. The BaO excitation spectrum from the reaction Ba + CO2 shows clear band heads and rotationally resolved features which can all be assigned. By contrast, the Ba + O2 excitation spectrum is markedly more complex since the band heads are missing and many high (v, J) levels are populated. The BaO rotational distributions for both reactions are found to be nonthermal, based on comparisons with simulated spectra. Estimates of the initial vibrational populations are also obtained. By extrapolation of the highest observed (v = 0, J) levels populated in the Ba + CO2 reaction, the dissociation energy of BaO has been determined to be D00 (BaO)=133.5± 1.3 kcal/mole. Since molecular beam investigations have shown that the Ba + O2 reaction proceeds through a long-lived collision complex, the experimental v = 0 rotational distributions have been compared with those calculated by phase space theory and transition state theory. The previous treatments of these statistical models have been extended to four-atom complexes. The results of the transition state theory reproduce the qualitative features of the experimental distributions, while the results of the phase space theory are in remarkable agreement with experiment. This strongly suggests that the dynamics of both reactions are governed by the formation of a long-lived collision complex.
Geometric constraints at triple points
Authors: Wheeler John C.
Published: February 2004

A class of rules concerning the disposition of phase boundaries at triple and multiple points in phase diagrams of single and multicomponent systems is discussed from a unified point of view. These rules, which may be referred to collectively as ``The 180° Rule,'' state that in a phase diagram with thermodynamically proper independent variables, no phase occupies more than 180° of angle at a triple point. A purely thermodynamic proof of the 180° rule is presented which relies only upon the convexity properties of thermodynamic potentials required by the second law of thermodynamics, and upon two explicit assumptions concerning the behavior of properties such as the entropy and number density as the triple point is approached. These auxiliary assumptions are shown to be essential: if either is violated, a model thermodynamic potential can be constructed which satisfies all of the requirements of convexity, yet violates the 180° rule. A distinction is emphasized between two fundamentally different types of intensive variables: ``fields'' such as temperature and pressure which must be the same in coexisting phases, and ``densities'' such as the entropy per unit volume and the molar volume which generally take on different values in coexisting phases. The phase diagram of a ``simple'' or one-component system is quite different in appearance according to whether both, one, or none of the independent variables are fields rather than densities. The 180° rule is proved in each of these cases. For the case when two densities are used as independent variables, the 180° rule takes on a stronger form which is known, for ternary systems, as Schreinemakers' rule. Generalizations of the 180° rule are discussed: to multicomponent systems, to quadruple and multiple invariant points, and to higher order phase transitions.
Intensities, line shifts, and resonance interference in zero-field optical double resonance
Authors: Bergeman T.
Published: February 2004

From resonance equations using density matrix formalism, we obtain several features of rf or mw optical double resonance experiments at zero field. Resonance signal intensity formulas are derived. The question of the spatial and polarization dependence is then reduced to a minimum number of parameters through the use of multipole tensors; the effect of a resonance within the excited state is formulated as a redistribution of excited state multipole moments. In the case of transitions between hyperfine sublevels which are separated on the order of the natural linewidth, coherence is produced by interference between different rf-optical transition pathways. Depending on the method of detection, such interference may lead to a dispersion-shaped contribution to the ODR line shape, as observed in the experiments on the NO A state (Bergeman and Zare, accompanying paper). Second order radiation field corrections for multiplet transitions (generalizations of the Bloch-Siegert shift) are also derived.
Correlation function formalism for the intrinsic viscosity of polymers
Authors: Yamakawa Hiromi , Tanaka Genzo , Stockmayer W. H.
Published: February 2004

A correlation function formalism for the intrinsic viscosity of polymers is studied. For this purpose, a Fokker-Planck equation and the momentum flux equation in the full phase space of the polymer are derived by an application of the projection operator method to the whole system consisting of the polymer and solvent molecules. These relations are further reduced to Kirkwood's Fokker-Planck equation and the corresponding flux in the polymer coordinate space. These steps give a molecular-theoretical basis to the Kirkwood equation, and the reduced flux obtained is essentially equivalent to that suggested previously by Stockmayer and co-workers. Some comments are made on related studies, particularly that of Doi and Okano, which is considered to be erroneous.
Near thermal energy charge transfer reactions of rare gas ions with diatomic and simple polyatomic molecules: The importance of Franck-Condon factors and energy resonance on the magnitude of the rate constants
Authors: Laudenslager James B. , Huntress Wesley T. , Bowers Michael T.
Published: February 2004

Charge transfer rate constants for reactions of He+, Ne+, Ar+, Kr+, and Xe+ with N2, O2, CO, NO, CO2, N2O, and CH4 were measured using an ion cyclotron resonance spectrometer. The absolute values of the rate constants were within the upper limit predicted from the Gioumousis-Stevenson orbiting theory for ion-molecule reactions. The magnitudes for the charge transfer rate constants are discussed with respect to (1) the availability of an energy level of the molecular ion resonant with the recombination energy of the rare gas ion, and (2) the value of the Franck-Condon factor connecting this energy level of the molecular ion with the molecular neutral.
Infrared spectrum of the HD–Ar van der Waals complex
Authors: McKellar A. R. W.
Published: February 2004

The infrared spectrum of HD–Ar, which occurs as fine structure accompanying the collision-induced fundamental band of HD near 2.7 μm has been studied in a mixture of HD and Ar at 85°K with an absorption path of 66 m. Spectra are observed accompanying the Q(0), Q(1), S(1), and S(0) transitions of HD, but only the latter is sufficiently strong and well resolved to be accurately measured. There is a close qualitative resemblence between the HD–Ar spectrum and previously observed spectra of H2–Ar and D2–Ar van der Waals complexes. However, a quantitative comparison shows a systematic difference which is probably due to the noncoincidence of the center of rotation of HD with its geometrical center.
Electrical conductivity of polysulfur nitride
Authors: Hsu Che-hsiung , Labes M. M.
Published: February 2004

Polysulfur nitride behaves like a one dimensional metal down to 4.2°K. The variability of the conductivity with crystal growth conditions is examined, with the best crystals showing room temperature conductivities of ∼1000 Ω−1·cm−1 along the chain axis, increasing by a factor of 11 to 13 down to 20°K and decreasing only slightly at lower temperatures. The apparent anisotropy of the conductivity is a factor of 50 at room temperature and a factor of 500 at 20°K. Thin films of (SN)x. can be prepared in which the conductivity has a low thermal activation energy presumably involving interparticle resistances. As the crystal samples improve in physical perfection, the low temperature conductivity tends to become significantly larger, and impurity scattering is observed at significantly lower temperatures.
Classical trajectory study of the unimolecular decomposition of H–C≡C–Cl, H–C≡C–H, and Cl–C≡C–Cl
Authors: Hase William L. , Feng Da-Fei
Published: February 2004

Monte Carlo rate constants and lifetime distributions for H–C≡C–H, H–C≡C–Cl, and Cl–C≡C–Cl at 200 kcal/mole were determined by classical trajectories. The Monte Carlo rate constants agree to within 30% of the RRKM prediction. Energy randomization is faster in Cl–C≡C–Cl than in H–C≡C–H and H–C≡C–Cl. An analysis of nonrandom lifetime distributions indicates that energy randomization is complete by 10−12 sec. for each of the molecules. Comparisons are made between our results and other unimolecular studies.
ENDOR spectra of 14N and H in free radicals formed by γ-irradiation of dimethylglyoxime single crystals
Authors: Nelson William H. , Atwater Frederick M. , Gordy Walter
Published: February 2004

The ENDOR spectra of the coupling nuclei in two species of radicals formed in γ-irradiated dimethylglyoxime have been measured. The more abundant of these has the form RC(CH3)NO with the unpaired electron concentrated on the NO group. This radical had been previously detected with ESR and the 14N nuclear magnetic coupling measured. With the ENDOR, we obtained the more accurate values A1 = 130.6±0.3 MHz, A2 = 73.9±1.0 MHz, and A3 = 68.6±0.8 MHz for the principal values of the magnetic coupling; in addition, we obtained the 14N nuclear quadrupole couplings, χ1 = −2.16±0.05 MHz, χ2 = +0.30±0.20 MHz, and χ3 = +1.92±0.20 MHz. The g values obtained, g1 = 2.0026±0.0002, g2 = 2.0070±0.0002, and g3 = 2.0099±0.0002, are in agreement with the earlier values. The second radical is one in which the unpaired electron interacts with two hydrogen nuclei with one set of coupling constants being A1 = 67.3±0.8 MHz, A2 = 42.7±0.9 MHz, and A3 = 19.3±0.3 MHz, and the other set of coupling constants being A1 = 63.8±0.2 MHz, A2 = 42.3±0.3 MHz, and A3 = 22.5±0.4 MHz. For both coupling nuclei, the eigenvectors corresponding to A3 are perpendicular to the molecular plane. Analysis of the data shows that the radical form is RC(NOH)CH2 with the -CH2 group in the molecular plane. The unpaired electron is in a π orbital perpendicular to the molecular plane with 67% of the spin density on the carbon of the CH2 group.
Mechanism for decay and spontaneous radiative decay constants of the lowest-lying attractive excited states of Ne2, Ar2, and Kr2
Authors: Oka T. , Rao K. V. S. Rama , Redpath J. L. , Firestone R. F.
Published: February 2004

Investigation of the kinetics of growth and decay of long-lived excited Ne2, Ar2 and Kr2 by means of fast absorption sepctrophotometry in the 810–995 nm region indicates that the predominant decay mode for these species is spontaneous radiative transition to the ground state at pressures from 200 to 1400 torr. No evidence for collisional steps in the decay mechanism has been found in this pressure range. Spontaneous radiative decay constants for Ne2 (3Σu+), Ar2 (3Σu+), and Kr2 (3Σu+) are 0.151(±0.003)×106, 0.310(±0.004)×106, and 2.83(±0.08)×106 sec−1, respectively.
X-ray photoemission molecular orbitals of hydrogen fluoride and the fluorinated methanes
Authors: Banna M. S. , Mills B. E. , Davis D. W. , Shirley D. A.
Published: February 2004

The x-ray photoemission molecular orbital spectra of gaseous hydrogen fluoride and the fluorinated methanes (CHn F4−n, 0≥ n ≥4) are reported. Ab initio, Koopman's theorem energies and a three-parameter relaxation model were used to fit the experimental binding energies. Excellent agreement was obtained. Relative intensities of molecular orbitals were computed using the model of Gelius with both CNDO/2 and ab initio atomic populations. In the case of ab initio results, net populations were found to be superior to gross populations in reproducing the experimental intensities. In most cases, the theory predicted intensities quite well. Some trends exhibited by the fluoromethane series are noted.
Molal volumes of K2SO4, K3Fe(CN)6, and K4Fe(CN)6 in water and in solutions of NaCl
Authors: Billi Alberto , Malatesta Francesco , Zamboni Roberto , Indelli Antonio
Published: February 2004

Pycnometric and dilatometric measurements have been made on solutions of K2SO4, K3Fe(CN)6, and K4Fe(CN)6 in water and in solutions 0.01442m, 0.03908m, 0.09044m of NaCl at 25°C. Deviations from the Debye—Hückel predictions even at very high dilutions are found for K2SO4 and K4Fe(CN)6. Some similarities are found with the predictions of the Mayer theory in the DHLL+B2 form, whereas the comparison is less favorable with the predictions of IPBE. As a general rule, when deviations from the Debye—Hückel theory are found in water solutions, the same kind of deviations are observed also in NaCl, even at very small concentrations of the multivalent electrolytes.
ESR and optical spectra of C2− in various ion pairs trapped at 4°K in solid argon
Authors: Graham W. R. M. , Dismuke K. I. , Weltner W.
Published: February 2004

C 2 − was prepared by photolysis of acetylene with and without the presence of Li, Na, K, or Cs atoms and trapped in argon at 4°K. With no alkali metal present, the optical bands at 5208 Å corresponding to the C2− gas-phase absorption at 5416 Å were obtained, but no ESR spectrum was observed. The countercation is not known in this case. In situ photolysis of metal-acetylene-argon matrices yielded new optical progressions at 4771 Å (Li), 4905 Å (Na), 5011 Å (K), and 5002 Å (Cs). ESR spectra were also observed exhibiting small (∼4 G) metal hfs and orthorhombic g tensors. 13C substitution confirmed that equivalent carbon atoms were present and that the ion pairs had C2ν symmetry. For Na+C2−, g1 = 2.0015(6), g2 = 2.0036(6), and g3 = 2.0124(30), where axis 2 is perpendicular to the plane of the ion pair and axis 3 is in the direction of the C–C bond. The g shifts resulting from distortion of the Σg+2 ground state of C2− correlate well with those expected for a 2A1 ground state for the ion pairs.
Irreversible thermodynamics of ideal dissipative systems
Authors: Hanson M. P.
Published: February 2004

For ideal dissipative systems of chemical reactions subject to time independent boundary conditions, it is shown that the general evolution criterion and excess entropy production of Glansdorff and Prigogine take on simple forms. The derived forms are used to discuss the conditions for stability of equilibrium and far-from-equilibrium stationary states. Additionally the effect of varying the size of a one-dimensional dissipative system is considered and a possible biological application is discussed.
ESR study of a bromine-containing radical in γ-irradiated bromomalonamide
Authors: Picone R. F. , Rogers Max T.
Published: February 2004

Both powder and single-crystal ESR spectra of two paramagnetic species formed by γ-irradiation of bromomalonamide at 77°K have been obtained. One radical shows a large bromine hyperfine interaction plus a small proton interaction and the g, A(81Br) and e2qQ(81Br) tensors have been determined from an analysis of the spectra of the deuterated form. The data have been interpreted as favoring the structure · CHBrCONH2 for this species. The second fragment has been identified as CONH2, but ESR parameters are not reported since it has been studied previously. Neither species is stable at room temperature in the host crystal.
Hydrogen elimination from carbon-silicon ion molecule reaction intermediates
Authors: Henis J. M. S. , Stewart G. W. , Gaspar P. P.
Published: February 2004

A detailed analysis of the isotopic distribution of the SiCX4+ product from the reactions SiH2++CD4 and SiD2++CH4 shows that the product distribution is clearly nonrandom and that X2 elimination from the silicon atom is favored by more than an order of magnitude over elimination from any other site. It is suggested that the observed selectivity may be related to the fact that silicon is the initial ionic center in both reactions studied.
Confirmation of a Ham effect in the 22 900 cm−1 band of Cs2ZrCl6:Ir4+
Authors: Yeakel W. C. , Slater J. L. , Schatz P. N.
Published: February 2004

A careful hot band study and high field Zeeman measurements using circularly polarized light confirm that the first strong line in the 22 900 cm−1 band of IrCl62− doped into cubic Cs2ZrCl6 can be assigned with confidence to the Jahn-Teller (Ham effect) quenched pair of no-phonon lines arising from the fully allowed charge-transfer transitions Eu″(2T2g)→ Eu″(2T2u)+Uu′(2T2u) as suggested previously by Piepho et al. and as further supported by the more recent detailed calculations of Yeakel and Schatz. This interpretation contrasts sharply with the recent Massuda and Dorain claim [J. Chem. Phys. 59, 5652 (1973)] that this line [and its ν1(a1g) progression] should be assigned to a parity-forbidden electronic transition activated by an ungerade vibration. Such an assignment is found to be inconsistent with the hot band data, and their accompanying Zeeman analysis is shown to be in error owing to misassignments of Zeeman components and their neglect of nonlinear effects (field-induced mixing). The specific arguments against the charge-transfer no-phonon interpretation are shown to be untenable. Several possible explanations of the splittings in higher members of the a1g progression are discussed.
A possible test of the photoexcited triplet mechanism of chemically induced electron spin polarization: Dependence of the spin polarization on polarized light orientation
Authors: Adrian Frank J.
Published: February 2004

Therè have been a number of observations of electron spin polarization in radicals produced by hydrogen atom abstraction or electron transfer reactions of photoexcited triplet molecules. Two mechanisms have been offered to explain the observed polarization: (1) The radical pair mechanism (RPM) in which the polarization results from mixing of the singlet and triplet states of the radical pair by the magnetic interactions within the radicals; (2) the triplet mechanism (TM) in which the polarization originates in the triplet as the result of spin selective intersystem crossing from the photoexcited singlet state. In the TM, the initial spin polarization is with respect to the molecular spin states of the triplet and evolves with time into a polarization with respect to the electron spin Zeeman levels in the external magnetic field. This process depends on the initial orientation of the triplet molecule with respect to the external field; thus, if a polarized photoexcitation source is used so that the initial distribution of molecular orientations is anisotropic, then the electron spin polarization of the radicals will depend on the orientation of the electric vector of the polarized light with respect to the magnetic field. This effect is both a possible test of the triplet mechanism, and a means of obtaining information about the excited states involved in the photochemical reaction.
Spectra and structure of phosphorus-boron compounds. X* Microwave, infrared, and Raman spectra and structure of dimethylphosphineborane
Authors: Durig J. R. , Hudgens B. A. , Li Y. S. , Odom J. D.
Published: February 2004

The infrared (33–4000 cm−1) and Raman (0–3500 cm−1) spectra of (CH3)2HPBH3, (CH3)2DPBH3, and (CH3)2HPBD3 have been recorded for the solid state at low temperature. The Raman spectra and polarization have been measured for the liquid state. The spectra have been interpreted in detail on the basis of Cs molecular symmetry. The barrier to internal rotation of the CH3 group in the solid state was found to be 3.8 kcal/mole. The microwave spectrum of (CH3)2HP11BH3, (CH3)2HP10BH3, (CH3)2DP11BH3, (CH3)2DP10BH3, (CH3)2HP11BD2H, and (CH3)2HP11BD3 was recorded from 18.0 to 40.0 GHz. An rs structure was determined for the BH3 group and an r0 structure was obtained from a least squares fit for the remainder of the structural parameters. The following molecular parameters were determined: r(BHs) = 1.212±0.005 Å, r(B–Ha) = 1.216±0.005 Å, r(P–B) = 1.898±0.010 Å, r(P–C) = 1.813±0.010 Å, r(P–H) = 1.414±0.009 Å, CPB = 114.6±1.0°, CPC = 105.4±1.0°, PBHs = 104.91±0.4°, PBHa = 104.81±0.4°, and BPH = 118.1±4.0°. The r(C–H) distance (1.093 Å) and the PCH angle (110.15°) were assumed. A dipole moment of |μa| = 4.77±0.02 D, |μc| = 0.90±0.05 D, and |μt| = 4.85±0.06 D were determined from the Stark effect.
Role of internal viscosity in polymer viscoelasticity
Authors: Allegra G.
Published: February 2004

A new theory of the internal viscosity in polymer chains is proposed. Although some of the conclusions are in agreement with the Kuhn-Cerf-Peterlin theories, the present approach is based on more rigorous statistical-mechanical grounds. However, the theory is unable to predict the exact value of the effective Arrhenius factor (A) related to the gauche⇄trans transitions between rotational states on the chain bonds. The internal viscosity force turns out to be a nonlinear effect of the chain motion. Confining our attention to the linear component, and assuming an oscillatory applied force, the diffusion equation is obtained as a modification of the corresponding equation formerly proposed by Zimm. For infinitely long chains the eigenvalue problem is exactly solved and, with reference to the free-draining model, the dynamic intrinsic viscosity of a polymer solution as well as the tensile and dielectric relaxation effects are calculated.
Correlation diagram for He + He → Be
Authors: Yarkony David R. , Schaefer Henry F.
Published: February 2004

An electronic correlation diagram has been calculated a priori for the model system He + He → Be. The suitability of different types of basis sets and of the Hartree-Fock approximation is discussed. The relation of this diagram to experimental inner shell collision chemistry is discussed briefly.
Dynamics of stiff polymer chains. I
Authors: Fixman M. , Kovac J.
Published: February 2004

The nonlinear configurational diffusion equation is formulated with bond vector coordinates. Primarily the treatment focuses on low amplitude oscillatory shear flow of the freely jointed chain, but the high frequency limit is formulated also with the constraint of constant bond angles, and is calculable fairly readily for a freely rotating chain or rotational isomeric model. The only numerical result given here concerns the high frequency limit [η]N∞ of freely jointed chains of N bonds. We find by perturbation theory that [η]N∞ ≃ [η]1∞ N[1+(N−1)/(6N)+⋯] (for the concentration measured in molecules/cubic centimeter; in conventional units of grams/cubic centimeter, [η]N∞ is asymptotically independent of N). In the lowest approximation the relaxing part of the intrinsic viscosity is given by equations quantitatively close to those of Zimm for the Gaussian model.
Nuclear magnetic resonance in antiferromagnetic α-RbMnCl3·2H2O
Authors: de Jonge W. J. M. , Swüste C. H. W.
Published: February 2004

α-RbMnCl3·2H2O is found to order antiferromagnetically at TN = 4.560±0.005 K. The magnetic array can be described by P2bc′ca′. The chains are antiferromagnetic. Values for the electric quadrupole coupling and the magnetic interaction parameters are reported for the Rb as well as for the Cl nucleus. The interpretation of the proton spectra gives rise to the assumption of a rather large spin reduction which agrees with the presumed one-dimensional character of these compounds.
Absorption spectra of NpCl3 and NpBr3
Authors: Carnall W. T. , Crosswhite H. M. , Pappalardo R. G. , Cohen D. , Fried S. , Lucas P. , Wagner F.
Published: February 2004

Low temperature absorption spectra are reported for NpCl3 and NpBr3 in the range 3300–40 000 cm−1. Term assignments are made to a number of excited levels not previously identified, and the data are interpreted in terms of a refined free-ion model. Some of the parameters associated with this model are found to have similar values for both 3+ actinide and lanthanide chlorides. The values determined for other of the parameters are in good agreement with those calculated independently using Hartree-Fock methods. The similar crystal-field quantum number ordering of levels in the ground states of actinide trichlorides and analogous lanthanides doped into LaCl3 is noted and discussed.
Photodissociation quantum yields of CO2 between 1200 and 1500 Å
Authors: Slanger Tom G. , Sharpless Robert L. , Black Graham , Filseth Stephen V.
Published: February 2004

Measurements of the photodissociation quantum yields of CO2 have been carried out using various atomic line sources between 1200 and 1500 Å. The production of CO was monitored by resonance fluorescence, and the results indicate that where the CO2 absorption spectrum is continuous, the CO quantum yield is high, but where there is structure, the yield is low. At the commonly employed 1236 Å resonance line, the CO quantum yield is 0.85±0.17, relative to the absolute value at 1470 Å of 0.75 obtained by Inn. On the same scale, the other values are (a) 1216 Å, 0.57 ±0.11, (b) 1302–1306 Å, 0.21±0.07, (c) ∼1390 Å, 0.46±0.05, (d) 1492–1495 Å, 0.58±0.06. The CO2 pressures employed were in the range 0.4–4.0 Torr. If these same quantum yields are valid at the pressures of the Mars and Venus atmospheres, the CO and O atom production rates are less than presently assumed.
Infrared spectra and anharmonic force field of NCO− in CsCl, CsBr, and Csl
Authors: Smith D. Foss , York Robert J.
Published: February 2004

The infrared spectra of NCO− isolated in CsCl, CsBr, and CsI have been obtained using the alkali halide pressed disk technique. Samples enriched with both 13C and 15N were prepared. The anharmonic force field of NCO− has been determined in each lattice using a simplified quartic force field. The anharmonicity constants, Xij, the anharmonic force constants, and the quadratic stretch-stretch interaction force constant have been determined to be essentially independent of the matrix.
Nuclear quadrupole coupling in the hydrogen molecule: A molecular orbital description
Authors: Snyder Lawrence C.
Published: February 2004

The electric field gradient at a nucleus of H2 has been computed from an SCF determinantal wavefunction in a Gaussian orbital basis set centered at the nuclei. It is found that both p and d polarization functions must be added if the true electric field gradient is to be represented within a few percent.
Abstraction fraction in the reaction of deuterium atoms with HBr and HI
Authors: Persky Avigdor , Kuppermann Aron
Published: February 2004

The reaction between D atoms and HX molecules (X=Br or I) may result in either abstraction of H atoms to yield HD+X or exchange of H atoms to yield DX+H. This reaction was studied at 300°K by photolyzing HX+DX+He mixtures with monochromatic light at two wavelengths. It was found that the abstraction fraction is 0.76±0.10 for X=Br and 0.88±0.08 for X=I. These results are discussed in terms of the dynamics of these reactions.
Model for H+2(v = 0)–He collisions above 2 eV
Authors: North G. R. , Harris H. H. , Leventhal J. J. , James P. B.
Published: February 2004

A classical model with no adjustable parameters employing Lennard-Jones type potentials is used to describe collision processes between H2+ (ν=0) ions and He atoms at relative energies above 2 eV. The assumptions that justify such an approach are discussed as well as the possibility of additional simplifications. Model predictions for collision-induced dissociation and reactive scattering cross sections compare favorably with data from four laboratories. Predicted angular distributions of product HeH+ and H2+ as well as vibrational and rotational energy partitioning for these products are also reported.
Inelastic scattering in atom-diatomic molecule collisions. I Rotational transitions in the sudden approximation
Authors: Stallcop James R.
Published: February 2004

The impact parameter method and the sudden approximation are applied to determine the total probability of inelastic rotational transitions arising from a collision of an atom and a homonuclear diatomic molecule at large impact parameters. An analytical approximation to this probability is found for conditions where the electron exchange or overlap forces dominate the scattering. An approximate upper bound to the range of impact parameters for which rotational scattering can be important is determined. In addition, an estimate of the total inelastic cross section is found at conditions for which a statistical model describes the scattering well. The results of this analysis are applied to Ar–O2 collisions and may be readily applied to other combinations of atoms and molecules.
Effect of pressure on 14N nuclear quadrupole relaxation in hexamethylenetetramine
Authors: Zussman Avigdor , Rapoport Eliezer
Published: February 2004

14N nuclear quadrupole resonance frequencies and spin-lattice relaxation time, T1, in hexamethylenetetramine (HMT) were measured as a function of hydrostatic pressure up to 6 katm at 257, 273, 294.5, 309, and 317°K. For the three higher isotherms T1 depends exponentially on pressure up to 3 katm. In this region T1 is determined mainly by molecular reorientation of the tetrahedral HMT molecule around its four threefold axes. This mechanism is discussed in terms of a simple activation process. The activation volume, ΔV*=23.6±1 cm3/mole, and activation enthalpy, ΔH*=17±1 kcal/mole were determined. From thermal expansion and compressibility data, the thermal pressure, Pt = T(∂p/∂T)v, of 6.2 katm and activation energy ΔE* = 12–15 kcal/mole were deduced. These values of ΔH*, ΔE*, and ΔV* are higher than the corresponding values reported by Anderson and Slichter for three other organic solids and might indicate the effect of the large number of hydrogen bonds in HMT.
Laser light scattering study of a ternary liquid mixture: Ethanol-water-chloroform
Authors: Chu B. , Lin F. L.
Published: February 2004

The intensity and Rayleigh linewidth of light scattered by concentration fluctuations in a ternary ethanol-water-chloroform system have been studied as a function of angle and temperature. Critical exponents γx, νx, and η obtained from the angular distribution of scattered intensity measured at constant compositions and different temperature distances from the plait point gave values of 1.50, 0.765, and 0.077, respectively. The results demonstrate the critical exponent renormalization, show first evidence of the nonzero critical exponent η in a three-component fluid system, and are not inconsistent with the scaling relations. In view of the renormalization which provides us with a stronger temperature dependence on the correlation length ξ, the critical region (K ξ> 1) can be reached even at T − Tc = 0.5°C. Thus, we are able to compare our experimental linewidth and hydrodynamic shear viscosity data with the Kawasaki theory at very large values of K ξ ≃ 50. Our experimental observations agree very well with the mode-mode coupling theory of Kawasaki after corrections for vertex, nonlocality, and frequency dependence of the shear viscosity and deviation of the Ornstein-Zernike correlation function.
Effective potential study of rotationally-vibrationally inelastic collisions between He and H2
Authors: Alexander Millard H.
Published: February 2004

Within the Rabitz effective potential formalism [J. Chem. Phys. 57, 1718 (1972)] we have carried out a three-dimensional, quantum mechanical study of He–H2 collisions, concentrating on rotationally-vibrationally inelastic processes. We treat the H2 molecule as a rotating Morse oscillator and use an interaction potential which is an analytic fit to the ab initio potential surface of Gordon and Secrest. Employing a modified version of the Gordon algorithm to solve the close-coupled equations, we have performed a series of calculations involving the collision of He with both ortho- and para-hydrogen at collision energies ranging 1.2–2.0 eV. We have carefully investigated the convergence properties of the close-coupled expansion. We present cross sections for all relevant rotational processes associated with the ν = 1 → ν =0 collision-induced vibrational relaxation of the H2 molecule. Our major conclusions are: (1) ∼20 rotational-vibrational states must be included; (2) large changes in the molecular angular momentum may accompany vibrational relaxation; (3) the degree of resonance of a particular rotation-vibration process may play an important role in determining the probability of the transition; and (4) the total cross section for vibrational relaxation increases significantly with increasing molecular rotational angular momentum.
Zeeman polarization measurements and the vibronic coupling of Re4+ in single crystals of K2PtCl6
Authors: Durocher Donald F. , Dorain Paul B.
Published: February 2004

Zeeman polarization measurements at 70 kG and 2°K of the t2g3, 4A2g, Γ8 to t2g3, 2T2g, Γ7 electronic and vibronic transitions of Re4+ in single crystals of K2PtCl6 have been performed. The right and left circular polarized spectra of the 0–0 transition are readily explained. It is shown that describing the vibronic excited states as arising solely from the coupling of the excited electronic state to the k = 0 vibrational modes of K2ReCl6 predicts incorrect selection rules. To describe the number of lines and observed polarization properties in the vibronic spectrum, it is necessary to consider the vibronic excited states as arising from the coupling of the impurity ion electronic state to the vibrations of the whole lattice and not simply to the k = 0 vibrations.
Theory of intermolecular pair correlations for molecular liquids. Applications to the liquids carbon tetrachloride, carbon disulfide, carbon diselenide, and benzene
Authors: Lowden Lawrence J. , Chandler David
Published: February 2004

The theory of molecular liquids based on the reference interaction site model (RISM) equation is used to describe the intermolecular structures of the liquids carbon tetrachloride, carbon disulfide, carbon diselenide, and benzene. The theory assumes that the equillibrium correlations between molecules in a dense fluid are determined primarily by the short range, harshly repulsive portions of the intermolecular potential. These repulsive interactions are modeled as hard core interactions by assuming molecules are composed of overlapping hard spheres which are rigidly fused together. The centers of the spheres are located at the positions of the nuclei in the molecules. As a result, the model hard core interactions depend on the molecular orientations. The equilibrium pair correlations produced by these interactions are determined from the solutions of the RISM integral equation. This is an approximate (but accurate) equation for the pair correlation functions. The molecular structure factors S(k) for the above mentioned liquids have been calculated from the theory. The only adjustable parameters in the theory are the diameters of the one or two distinct atomic spheres on a molecule. With physically reasonable values for the diameters, the theoretical results for S(k) agree closely with the results obtained from neutron or x-ray scattering experiments. From the r-space representation of the pair correlation functions, the theory leads to an unambiguous interpretation of the intermolecular structures of the different liquids. For liquid carbon tetrachloride, it is found that the CCl4 molecules form an interlocking structure which gives rise to important orientational correlations between molecules in the liquid. Nearest neighbors in both the liquids carbon disulfide and carbon diselenide tend to be aligned parallel to one another. In liquid benzene, nearest neighbors tend to be perpendicular to each other. These interpretations are discussed in detail. Suggestions are made for future experimental work. Comments are made concerning the usefulness of the RISM equation.
Molecular scattering equations derived from the rotational invariance of wave operators
Authors: Hunter L. W. , Snider R. F.
Published: February 2004

It is shown that the rotational invariance of the Mo/ller wave operator can be used directly to derive the scattering equations of Curtiss and co-workers. An equation for the reactance matrix is also derived by the same method.