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15 Jun 1979

Volume 70, Issue 12, pp. 5343-5926

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Electron energy loss spectroscopy of pristine and radiation damaged polyethylene

John J. Ritsko

J. Chem. Phys. 70, 5343 (1979); http://dx.doi.org/10.1063/1.437465 (7 pages) | Cited 35 times

Online Publication Date: 28 July 2008

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The spectra of valence and core electronic excitations of polyethylene from 1 to 390 eV were measured with a resolution of 0.11 eV by transmission electron energy loss spectroscopy. Structure at 9.5, 13.2, 14.7, 16.6, 19.6, 21.6 eV and a continuum of core excitations beginning at 287.5 eV was measured and compared with theoretical calculations of molecular excitons and interband transitions. The momentum dependence of the fundamental absorption threshold at 7.2 eV indicates that the absorption edge is due to highly localized excitons. From the energy loss spectra the complex dielectric response function and optical properties were calculated and compared with existing optical data. Radiation induced changes in the electronic structure were observed by their characteristic excitation spectra which were shown to be due to formation of polyenyl chromophores in the polymer backbone.
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61.80.Lj Atom and molecule irradiation effects

Knudsen effusion mass spectrometric determination of the dissociation energy of diniobium, Nb2(g), and the heat of sublimation of solid niobium

Satish K. Gupta and Karl A. Gingerich

J. Chem. Phys. 70, 5350 (1979); http://dx.doi.org/10.1063/1.437466 (4 pages) | Cited 9 times

Online Publication Date: 28 July 2008

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The dimer of niobium, Nb2(g), has been observed under thermal equilibrium conditions by the high temperature mass spectrometric technique, employing an unconventional design for the Knudsen cell. From the partial pressures of Nb and Nb2 measured in the 2545–2677°K temperature range, the dissociation energy of Nb2(g) has been determined to be D0°=503±10 kJ mole−1 or 120.2±2.4 kcal mole−1 and D°298=511±10 kJ mole−1 or 122.0±2.4 kcal mole−1. By combining D (Nb2) with the heat of vaporization of niobium, the heat of formation of Nb2(g) is derived as ΔH°f,298=916±12 kJ mole−1 or 218.9±2.9 kcal mole−1. Also, the heat of vaporization of Nb has been redetermined as ΔH°v,298=713±7 kJ mole−1 or 170.4±1.6 kcal mole−1 and ΔH°v,0=710±7 kJ mole−1 or 169.7±1.6 kcal mole−1. The dissociation energy of Nb2(g) is in good agreement with the value predicted previously and is consistent with the trends indicated for the dissociation energy of the diatomic molecules of the first and second transition series metals.
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33.15.Fm Bond strengths, dissociation energies

On the temperature dependence of the 14N NQR in K‐TCNQ

Juan Murgich

J. Chem. Phys. 70, 5354 (1979); http://dx.doi.org/10.1063/1.437467 (4 pages) | Cited 4 times

Online Publication Date: 28 July 2008

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The temperature dependence of the 14N nuclear quadrupole resonance (NQR) spectrum of K‐TCNQ was measured from 77 to 300 K. The NQR frequency shifts with temperature can be explained by considering the effects of the thermal averaging of the quadrupole parameters and the rearrangement of the TCNQ− and K+ stacks. The 14N NQR data are consistent with the observed Peierls transition found for K‐TCNQ.
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33.25.+k Nuclear resonance and relaxation

ESR studies of a nitrogen defect in irradiated potassium azide

R. C. Turner, F. H. Stout, and T. G. Trimm

J. Chem. Phys. 70, 5358 (1979); http://dx.doi.org/10.1063/1.437468 (4 pages)

Online Publication Date: 28 July 2008

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An electron spin resonance study has been conducted on a new paramagnetic defect center in irradiated potassium azide. Irradiation of a single crystal of KN3 with x rays at 77 K resulted in the formation of the defect which was characterized by a single structureless resonance line having considerable anisotropy. Effective g values along the principal axes were measured at 77 K and were found to be 6.16, 1.719, and 0.579 along the crystal [001], [110] and [110] directions, respectively. The rotational spectra could not be fit, however, with a spin one half Zeeman Hamiltonian, leading to the conclusion that only one transition of a spin greater than one half system was being observed. Measurements at temperatures other than 77 K showed a strong temperature dependence of the effective g values which would be consistent with a temperature dependent fine structure term in the spin Hamiltonian. The defect was found to be stable to about 130 K. Isothermal annealing measurements indicated a first order decay with an activation energy of 0.39 eV and a characteristic frequency of about 1012 Hz. Irradiation of a single crystal with ultraviolet light resulted in the formation of a defect with the same effective g values, but a narrower resonance line having hyperfine structure indicative of interaction with a single nitrogen nucleus.
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61.05.Qr Magnetic resonance techniques; Mössbauer spectroscopy (for structure determination only)
61.72.J- Point defects and defect clusters

Franck–Condon theory of chemical dynamics. VI. Angular distributions of reaction products

Carlos L. Vila, David J. Zvijac, and John Ross

J. Chem. Phys. 70, 5362 (1979); http://dx.doi.org/10.1063/1.437469 (14 pages) | Cited 12 times

Online Publication Date: 28 July 2008

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We calculate planar and three‐dimensional angular distributions for the products of atom–diatom chemical reactions by means of the Franck–Condon (FC) model. The wave functions on the reactant and product quasiadiabatic surfaces are expanded in partial wave series. A local uncoupling of the different degrees of freedom, as justified earlier, is assumed and consequently the individual members of the partial wave series can be separated into products of angular factors and rovibration–translation factors. To evaluate these factors, we consider the limit of weak and strong potential, and weak and strong kinematic couplings. The center of mass differential cross section is obtained by means of the T matrix formalism, where the T matrix is approximated by a generalized Franck–Condon overlap of the reactantlike and productlike wave functions. We use several further satisfactory approximations, e.g., linearization of the potential in the region of maximal overlap, and semiclassical approximation to the oscillator wave functions, beyond those of the FC model to obtain an analytic expression for the T matrix. For assumed LEPS surfaces of the systems H+H2 →H2+H, H2+F→HF+H and H+Cl2→HCl+Cl, we calculate angular distributions of reaction products in the various coupling limits for ranges of final states. The angular distributions in the strong potential coupling limits have a Gaussian shape peaked about the backscattering angle (π) (the hard sphere deflection angle for the chosen critical configuration) for each of the three reactions studied. In all three cases the 3D angular distribution is narrower than the planar (2D) angular distribution. Our calculations show no difference between the angular distributions of the weak and strong kinematic coupling limits. The angular distribution of the 2D weak potential coupling case are broader than those of the strong potential coupling. For H+H2 we find our results in the strong potential limit to be in qualitative agreement with exact quantum mechanical calculations. The angular distribution for a given product state broadens as the initial relative kinetic energy is increased, in agreement with classical trajectory calculation (F+H2). The angular distribution is also predicted to broaden as the final relative velocity increases, in agreement with experiment (H+Cl2, F+H2). Finally we introduce several simplifying approximations to our analytical model and find that, for exothermic reactions like F+H2, the radial contribution to the T matrix is dominated by certain features of the potential: the barrier width, the slope of the potential on the reactant side, and force constants in the region of maximum overlap. Our analysis provides a basis for the formulation of reduced variables which may be of use in comparing reactions. Finally we discuss some sufficient conditions for the separability of product velocity and angular distributions.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Rotational dependence of the dipole moment of CH3D

James K. G. Watson, Michio Takami, and Takeshi Oka

J. Chem. Phys. 70, 5376 (1979); http://dx.doi.org/10.1063/1.437470 (5 pages) | Cited 22 times

Online Publication Date: 28 July 2008

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Radio frequency modulated side bands of the C18O2 P (18) laser line were used to perform infrared–infrared double resonance between the first order Stark components of the ν6 rP (10,1) transition of CH3D. The dipole moment in the J=10, K=1 level in the ground state has been measured to be (1.03±0.1) ×10−3 D, which is very different from the previously reported values of around 5.65×10−3 D. This difference has been explained as due to rotational dependence of the dipole moment. Combining the present result with the previous molecular beam measurements by Wofsy, Muenter, and Klemperer, we have obtained the rotational dependence of the dipole moment derived from Stark measurements in the form μStark(J,K) =∓{ (5.657±0.004)−(0.0427±0.0009) J (J+1) +(0.0696±0.0026) K2}×10−3 D. The upper sign would be consistent with ab initio calculations of the signs of the dipole derivatives. A theory was developed to calculate the above coefficients of J (J+1) and K2 for CH3D. It has been demonstrated that they can be completely predicted from the ϑzxy parameter of CH4. The prediction agreed with the observed values within the quoted uncertainties. This theoretical information was indispensable in determining which of the two observed double resonance signals corresponded to the ground state. The apparent contradiction of the present result with that of Ozier, Ho, and Birnbaum, who reported that the dipole moments of CH3D determined from the intensities of R branch spectral lines are independent of J, is explained as due to the fact that the rotational dependence of the dipole moment is different depending on the method of determination. Their measurements are shown to be consistent with the above parameters.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects

NMR dynamic frequency shifts and the quadrupolar interaction

Lawrence G. Werbelow

J. Chem. Phys. 70, 5381 (1979); http://dx.doi.org/10.1063/1.437471 (3 pages) | Cited 35 times

Online Publication Date: 28 July 2008

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A brief account of the quadrupolar interaction is presented. It is demonstrated that second‐order dynamic frequency shifts must be considered for multipolar nuclides relaxed by spacially isotropic quadrupolar interactions. Hence, each single quantum coherence is characterized by a unique precessional frequency. A short discussion of the intensities and evolution of these transverse magnetization composites is also included for completeness. The findings of this work supplement the theory of spin 3/2 quadrupolar labelling and exchange techniques as applied to biomolecular systems.
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33.25.+k Nuclear resonance and relaxation

Deductions about the structure of phase III from thermodynamic measurements on solid isotopic methanes

M. A. White and J. A. Morrison

J. Chem. Phys. 70, 5384 (1979); http://dx.doi.org/10.1063/1.437472 (7 pages) | Cited 11 times

Online Publication Date: 28 July 2008

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In a continuing study of the solid isotopic methanes, the heat capacity of solid CHD3 has been measured in the range 0.15<T<3 K. Some structure is found in a Schottky anomaly in the region of the measurements and it is related to the composition of nuclear spin symmetry species in the solid. There is no evidence of spin conversion. The entropy of CHD3 has been calculated as a function of temperature from the heat capacity and other data, and is used to make deductions about quantum disorder in the solid. Combined results for CH3D, CH2D2 and CHD3 lead to the conclusion that the structure of phase III of solid methane is quantum disordered and that it must contain at least three types of sublattice. A model consisting of two sublattices with tetrahedral molecular fields and one with symmetry lower than tetrahedral, accounts for the experimental observations satisfactorily.
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81.30.Dz Phase diagrams of other materials
31.30.Gs Hyperfine interactions and isotope effects

Generalizations of the direct CI method based on the graphical unitary group approach. I. Single replacements from a complete CI root function of any spin, first order wave functions

Per E. M. Siegbahn

J. Chem. Phys. 70, 5391 (1979); http://dx.doi.org/10.1063/1.437473 (7 pages) | Cited 79 times

Online Publication Date: 28 July 2008

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The direct CI method is generalized to the class of wave functions, denoted as first order wave functions. With a first order wave function is meant a complete CI expansion in a small internal valence space and single excitations outside this space. The wave function can have any spin. The formalism of the graphical unitary group approach of Paldus and Shavitt is used to reduce the coupling coefficients of the direct CI method to expressions involving the internal space only. The necessary formula tape is therefore reduced drastically in size. An approximate and much faster method is suggested for very large CI expansions, based on the neglect of certain integrals. The method is applied to the singlet–triplet splitting of dioxymethane, CH2O2, which is a proposed intermediate in the ozonolysis of ethylene. The calculations predicts the 1A1 to be the ground state, but the splitting between 1A1 and 3B2 is calculated to be very small, 2.0 kcal/mole, in the best calculations reported here.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

Low energy x‐ray emission spectra and molecular orbital analysis of CH4, CCl4, and CHCl3

Rupert C. C. Perera and Burton L. Henke

J. Chem. Phys. 70, 5398 (1979); http://dx.doi.org/10.1063/1.437474 (9 pages) | Cited 7 times

Online Publication Date: 28 July 2008

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The C–K and Cl–LII,III low‐energy x‐ray spectra from solid CCl4, CHCl3, and the C–K x‐ray spectrum from solid CH4 have been obtained using monoenergetic x‐ray excitation and a lead myristate multilayer analyzing crystal. The C–K spectrum of methane and Cl–LII,III spectra of the chloromethanes were also measured in the gas/vapor phase and compared with those measured in the solid phase. The deconvolved spectral components are aligned on a common energy scale with the complementary x‐ray emission and photoelectron spectra by identifying the same molecular orbital in all spectra. Such an alignment procedure yields a C‐ls ionization energy of gaseous CH4, and solid CCl4 and CHCl3 as 290.0 293.5 and 293.1 eV, respectively; and the Cl‐2p3/2 ionization energy of solid CCl4 and CHCl3 as 206.5 and 204.8 eV. Results of the CNDO/2 and MINDO/3 MO calculations have been presented and compared with the available results of the extended Hückel MO method and with the deconvolved spectral components. From the geometry program in the MINDO/3 MO calculation, the C–H bond length in CH4 is 1.102 Å, the C–Cl bond length in CCl4 is 1.751 Å, and the C–H and C–Cl bond lengths in CHCl3 are 1.100 and 1.744 Å, respectively. Comparison with the vapor/gas phase spectra shows essentially the same energies for spectral components in the C–K and Cl–L spectra from CH4 and CCl4, whereas the spectral components in the Cl–L spectra of CHCl3 have energies in the gas phase that are significantly higher than those for the solid phase.
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33.20.Rm X-ray spectra

The 2 1Ag–1 1Bu energy gap in the polyenes: An extended configuration interaction study

Paul Tavan and Klaus Schulten

J. Chem. Phys. 70, 5407 (1979); http://dx.doi.org/10.1063/1.437475 (7 pages) | Cited 93 times

Online Publication Date: 28 July 2008

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For a correct account of the ordering of excited states in the polyenes, in particular the low‐lying 2 1Ag and 1 1Bu states, single as well as double excited configurations must be included in a CI expansion. However, for longer π systems such expansion shows, in contrast to spectroscopic observations, a divergence of excitation energies and a reversal of the 2 1Ag and 1 1Bu state ordering. We have therefore extended the CI expansion to include all triple and quadruple excitations for the polyene series CnHn+2’ n=4,6,8,10,12 and n=4,6,8,10, respectively. In our calculations we employed a PPP model Hamiltonian. The extended CI expansions correct the faults of previous treatments and predict an increase of the 2 1Ag–11Bu energy gap with increasing polyene length in agreement with recent spectroscopic observations. The effect of higher excitations is mainly due to triple excitations involving three simultaneous spin flips of ground state electrons.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

Correlation effects in the spectra of polyacenes

Paul Tavan and Klaus Schulten

J. Chem. Phys. 70, 5414 (1979); http://dx.doi.org/10.1063/1.437452 (8 pages) | Cited 30 times

Online Publication Date: 28 July 2008

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In order to describe the electron correlation in the excited singlet π,π∗ states of the polyacenes [C4n+2H2n+4], we have carried out PPP–SCF–CI calculations including all single and double excitations in the CI expansion up to n=5, including all triple excitations up to n=3, and all quadruple excitations up to n=2. Compared to previous CI descriptions which included single excitations only, e.g., the classic work of Pariser [J. Chem. Phys. 24, 250 (1956)], our calculations lead us to predict the following: (1) ’’new’’ excited states entailing the promotion of two electrons from the ground state (some of them predicted previously by other authors), and (2) a partial reordering of those (well‐known) excited states already accounted for by a S‐CI representation. Single and double excitations in a CI expansion (D‐CI) satisfactorily describe the ordering of all excited states up to 7 eV; the effect of higher excitations is to correct the excitation energies overestimated by the D‐CI description. Our predicted spectra provide a consistent assignment of all one‐ and two‐photon spectral data but do not yield a quantitative agreement.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

Rate constants for the reactions of atomic boron with O2, SO2, CO2, and N2O

U. C. Sridharan, T. G. DiGiuseppe, D. L. McFadden, and P. Davidovits

J. Chem. Phys. 70, 5422 (1979); http://dx.doi.org/10.1063/1.437453 (5 pages) | Cited 12 times

Online Publication Date: 28 July 2008

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The gas phase reactions of atomic boron with O2, SO2, CO2, and N2O have been studied using a diffusion flame technique. Atomic boron is produced in a microwave discharge of 1% B2H6 in helium and diffuses into a chamber containing the oxidizer also diluted in helium. The temperature was approximately 300 °K. The rate constants were determined from atomic absorption measurements of boron density in the flame. The rate constants for the O2 and SO2 reactions are (9±7) ×10−12 cm3 molecule−1sec−1 and (7±5) ×10−12 cm3 molecule−1sec−1, respectively. An upper limit of 5×10−13 cm3 molecule−1sec−1 is estimated for the rate constants of the CO2 and N2O reactions.
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34.50.Lf Chemical reactions

Two‐photon spectroscopy of dipole‐forbidden transitions. II. Calculation of two‐photon cross sections by the CNDO–CI method

Georg Hohlneicher and Bernhard Dick

J. Chem. Phys. 70, 5427 (1979); http://dx.doi.org/10.1063/1.437454 (11 pages) | Cited 49 times

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In the first paper of this series we investigated the applicability of a CNDO/S scheme including double excited configurations for the calculation of excitation energies of larger unsaturated molecules. In this paper we show that the same scheme is very useful for the prediction of two‐photon transition probabilities. If the proper expansion is used, the results converge quite well with increasing number of intermediate states. We also show that the inclusion of double excited configurations is not only necessary to obtain better energies for dipole‐forbidden transitions to ’’covalent’’ excited states but also to obtain the correct order of magnitude for two‐photon cross sections.
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31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)

Depolarized light scattering by simple liquids

T. Keyes

J. Chem. Phys. 70, 5438 (1979); http://dx.doi.org/10.1063/1.437455 (4 pages) | Cited 5 times

Online Publication Date: 28 July 2008

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A new theory is presented for the scattering of light by simple fluids. The theory naturally leads to the idea that, in multiple scattering by a group of spherical particles, the shape of the region excluded (’’shaped cavity’’) by the group to the rest of the system is of considerable importance. The large existing disagreement between theoretical and experimental scattering intensities for simple liquids is explained using the shaped cavity idea, which has already been used most successfully for scattering from nonspherical molecules.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)

The role of intermolecular potential well depths in collision‐induced state changes

H.‐M. Lin, Mark Seaver, K. Y. Tang, Alan E. W. Knight, and Charles S. Parmenter

J. Chem. Phys. 70, 5442 (1979); http://dx.doi.org/10.1063/1.437456 (16 pages) | Cited 120 times

Online Publication Date: 28 July 2008

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A relationship is developed from two distinct theoretical approaches to correlate the rate constants kM or cross sections σM for a series of added gases M which collisionally induce a state transformation A∗→B. The correlation derived from theory is where C is a constant and ϵA∗M is the intermolecular well depth between A∗ and M. We observe that experimental data can be described by a related correlation where β is a constant and ϵMM is the well depth between pairs of M molecules. This correlation is shown to be general. It works for electronic state deactivation in atoms, intersystem crossing and internal conversion in S1 polyatomics, rotational and also vibrational relaxation in S1 polyatomics, predissociation in diatomics and polyatomics, and vibrational relaxation in a free radical as well as in a molecular ion. The theory is appropriate only when attractive forces dominate the interaction, and this seems consistent with the experimental data. The correlation thus provides a simple means to distinguish between attractive and repulsive interactions. The correlation also reveals that collision partners do not substantially modify the intrinsic S1‐T mixing during collision‐induced intersystem crossing.
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34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)

A method to estimate intermolecular potential well depths for species in both ground and excited electronic states

Charles S. Parmenter and Mark Seaver

J. Chem. Phys. 70, 5458 (1979); http://dx.doi.org/10.1063/1.437457 (5 pages) | Cited 41 times

Online Publication Date: 28 July 2008

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The relationship lnσM=lnC+[(ϵA∗A∗) (ϵMM)]1/2/kT correlates the cross sections σM for a state change A∗→B induced by a series of added M gases with the intermolecular potential well depths for A∗...A∗ pairs and M...M pairs. This correlation is used with literature data concerning A∗→B to deduce ϵA∗A∗ for electronically excited atoms (Na, Ne, Ar, Xe) and electronically excited molecules (I2, SO2, CH3OH, glyoxal, propynal, benzene). The well depths are generally observed to exceed the ground state values by factors of 2–10. Large well depths are also observed for sec‐butyl radicals and for the C5H9+ ion with high vibrational excitation. The correlation also provides an alternate means to measure ground state well depths ϵMM. In cases where secure comparisons are available, the well depths so derived usually lie within 20% of values found from transport measurements or virial coefficients. The correlation seems a useful alternative to empirical estimating procedures when data from conventional methods are not available.
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34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)

Dissociating states of the H−3 system

Ramiro Garcia G., Angelo R. Rossi, and A. Russek

J. Chem. Phys. 70, 5463 (1979); http://dx.doi.org/10.1063/1.437458 (5 pages) | Cited 7 times

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Single determinant Hartree–Fock calculations for the lowest singlet and triplet potential energy surfaces of the H−3 system are presented over a broad range of isosceles triangular configurations of the nuclei. The addition of a diffuse s function to the four‐term Gaussian expansion of Huzinaga for H(1s) together with p type polarization functions produces results which are in agreement with experiments on double electron capture by H+3 to form H−3. The present calculations predict that capture to the ground singlet state produces H2+H−, with a dissociation energy in reasonable agreement with the experimental findings. Capture to the triplet state is predicted to resulted in the three body dissociation H+H+H− with small dissociation energy. This is consistent with, but not positively confirmed by, the experimental data.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions

IR absorption of SF6 excited up to the dissociation threshold

W. Fuss and J. Hartmann

J. Chem. Phys. 70, 5468 (1979); http://dx.doi.org/10.1063/1.437459 (9 pages) | Cited 21 times

Online Publication Date: 28 July 2008

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SF6 was pumped by a P20 TEA CO2 laser up to an average energy of 10 000 cm−1 in the absence of collisions and up to 20 000 cm−1 with a certain collisional relaxation. A second CO2 laser, very much attenuated, was used to determine absorption cross sections for frequencies from 915 to 985 cm−1. No coherent effects and no collisionless relaxations were found, in contrast to measurements with a cw laser as a probe. The ν3 band continuously shifts to longer wavelengths, but the shift of the ν2+ν6 band is 10 to 20 times smaller. Many more rotational states of the vibrational ground state are depopulated than expected. To explain it we suggest direct two‐photon excitation, for which independent evidence is also presented. Many peaks and holes were found, part of which we assign to high states. Evidence for inhomogeneity of these structures is found by comparison with single laser absorption spectra. Collisional relaxation of unidentified nature and with a time constant of 48±10 ns mbar generates new spectra, indicating large nonequilibrium rotational populations.
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33.20.Ea Infrared spectra

Coupled‐channel study of halogen (2P) + rare gas (1S) scattering

C. H. Becker, P. Casavecchia, Y. T. Lee, R. E. Olson, and W. A. Lester

J. Chem. Phys. 70, 5477 (1979); http://dx.doi.org/10.1063/1.437460 (12 pages) | Cited 51 times

Online Publication Date: 28 July 2008

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Quantum mechanical coupled‐channel (CC) scattering calculations are reported using realistic adiabatic potentials for the 2P+1S interaction of F–Ar, F–Xe, and Cl–Xe. Differential cross sections dσ/dω derived from a simple elastic approximation appropriate for large spin orbit interactions accurately reproduce all the gross features computed by the coupled‐channel method. This finding supports the extraction of interaction potentials from laboratory differential cross sections I (ϑ) via an elastic analysis. Integral inter and intramultiplet changing cross sections are expressed conveniently in terms of Grawert’s B(j, j’;g) coefficient. Information on the collision dynamics is extracted by following the partial wave dependence of selected B(j, j’;g). Classical turning point analysis, based on the values of the large l‐waves for which these partial wave contributions Bl(j, j’;g) begin to rise above zero, leads to the conclusion that both intermultiplet and first order forbidden intramultiplet transitions are caused by a single localized nonadiabatic coupling region at the position of complex crossing of the Ω=1/2 adiabatic potentials. Small amplitude oscillations or perturbations in the CC calculated dσ/dω and in the experimental I (ϑ) are thought to be examples of Stükelberg oscillations, though quantitative agreement between these quantities is not obtained. The energy dependence and interference structure of the computed B(j, j;g) are briefly discussed, as is the approximation of the constant spin orbit interaction over the experimentally accessible range of internuclear distances.
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34.50.-s Scattering of atoms and molecules

Effect of irradiation temperature from 77 to 1.6 K on the optical absorption and scavenging efficiency of localized electrons in aqueous 10 M lithium chloride glasses

G. Dolivo and Larry Kevan

J. Chem. Phys. 70, 5489 (1979); http://dx.doi.org/10.1063/1.437461 (5 pages) | Cited 2 times

Online Publication Date: 28 July 2008

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Irradiation of the 10 M LiCl/D2O matrix at 77 K stabilizes the solvated electron species, evis−(λmax∼575 nm) while irradiation at 4.2 or 1.6 K stabilizes two localized electron species evis−(λmax∼680 nm) attributed largely to solvated electrons and eIR−(λmax≳2400 nm) attributed largely to presolvated electrons. Between 4.2 and 1.6 K the evis− spectrum is essentially unaffected but the eIR spectrum is shifted to lower energy at 1.6 K. The electron scavenging efficiencies of bromate, nitrate, and chromate for evis− at 77, 4.2, and 1.6 K and for eIR− at 4.2 and 1.6 K were studied. The total scavenging efficiency for all localized electrons in the glass increases as the temperature is lowered over this range. An apparent low scavenging efficiency for evis− at 4.2 K seems due to competitive tunneling to the scavenger by evis− and eIR−. This interpretation is supported by observations of the scavenging efficiency of nitrate in 10 M NaOH aqueous glass over this same temperature range in which only one main type of localized electron species is observed. The scavenging results support the assignments of e−IR to a presolvated electron with a nonequilibrium orientation of first solvation shell waters and of e−vis to a solvated electron with an equilibrium orientation of first solvation shell waters.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

Glass tricritical points

F. Dowell

J. Chem. Phys. 70, 5494 (1979); http://dx.doi.org/10.1063/1.437462 (4 pages) | Cited 1 time

Online Publication Date: 28 July 2008

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The theoretical discovery of a symmetrical tricritical point in a binary mixture of polymeric glasses is reported. A mean field simple cubic lattice model for mixtures of semiflexible chain molecules having simple Lennard‐Jones interactions has been used to calculate the phase diagram of the system. Effects of pressure on the mixture have also been studied.
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64.60.Kw Multicritical points

Thermal effects on the optical spectra of a polydiacetylene: Poly{1,2‐bis [4‐ (isopropylcarbamoyloxy) ‐n‐butyl]‐1‐buten‐3‐ynylene}

H. Eckhardt, C. J. Eckhardt, and K. C. Yee

J. Chem. Phys. 70, 5498 (1979); http://dx.doi.org/10.1063/1.437463 (5 pages) | Cited 33 times

Online Publication Date: 28 July 2008

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The reflection spectra of single crystals of the polydiacetylene, IPUDO [R= (CH2)4OCONHCH (CH3)2], were measured between 25° C and 160° C. A nearly reversible thermochromic change is observed together with a variation of hysteresis upon cycling. The latter is attributed to annealing that permits the pendant groups to adopt a conformation which favors the butatriene‐type configuration of the polymer at high temperatures. Intensities of the high and low temperature spectra obtained by Kramers–Kronig transforms are in excellent agreement with the spectral intensities of polydiacetylenes which are prototypes for the two configurations.
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36.20.Kd Electronic structure and spectra

Excited states and photochemistry of saturated molecules. VII. Potential energy surfaces in excited singlet states of methane

Mark S. Gordon and James W. Caldwell

J. Chem. Phys. 70, 5503 (1979); http://dx.doi.org/10.1063/1.437464 (12 pages) | Cited 32 times

Online Publication Date: 28 July 2008

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Potential energy surfaces are investigated for a number of low‐lying excited singlet states of methane, using a split valence plus Rydberg basis set and singly excited CI. Of the six minima found, the lowest two are valence states. The lowest minimum corresponds to the products 1 1B1 CH2+1 1Σg+ H2, in agreement with the observed threshold photochemistry, and is accessible by five separate routes from the lowest vertical state. The second valence minimum is a square planar structure. Of the four Rydberg minima detected, one is a local minimum on the otherwise dissociative B1 surface and two correspond closely to CH4+ structures previously determined. None of the minima have a structure from which the radical products CH3⋅+H⋅ are likely to be obtained.
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82.20.Kh Potential energy surfaces for chemical reactions

Vibrational averages of x‐ray and high energy electron scattering intensities from diatomic molecules

Joel Epstein and Robert F. Stewart

J. Chem. Phys. 70, 5515 (1979); http://dx.doi.org/10.1063/1.437476 (7 pages) | Cited 7 times

Online Publication Date: 28 July 2008

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Ground‐state vibrational averages of the intensities of x‐rays and high‐energy electrons elastically scattered by N2 (1Σ+g), CO (1Σ+), BF (1Σ+), and FH (1Σ+) have been calculated. When nonrigid contributions are included, the vibrational averages are accurately computed from generalized x‐ray scattering factors at the [2‖2] level. Maximum anharmonic contributions to the average intensities are 0.3%–0.5%. Contributions from nonrigid pseudoatom components are generally smaller by an order of magnitude and are negligible for S greater than 10 Å−1.
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78.70.Ck X-ray scattering
34.80.Bm Elastic scattering
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