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1 Jun 1970

Volume 52, Issue 11, pp. 5499-5976

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New Adsorption Isotherm for Heterogeneous Surfaces

Dwarika Nath Misra

J. Chem. Phys. 52, 5499 (1970); http://dx.doi.org/10.1063/1.1672815 (3 pages) | Cited 35 times

Online Publication Date: 8 September 2003

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A general method is proposed to obtain adsorption isotherms for heterogeneous surfaces from the arbitrary energy distribution functions if the Langmuir isotherm represents the individual homotattic sites. The method is limited to the temperature dependent distribution functions only. It is observed that the number of distribution functions, yielding physically meaningful isotherms, is extremely restricted on mathematical grounds. The method yields only one adsorption isotherm that is new and simple; the corresponding distribution function, however, seems to be more characteristic of homogeneous surfaces having a strictly limited energy distribution rather than that of heterogeneous surfaces with a wide variation of distributive energies.

Flash Photolytic Production, Reactive Lifetime, and Collisional Quenching of O2(b1Σg+,υ′  =  0)

S. V. Filseth, A. Zia, and K. H. Welge

J. Chem. Phys. 52, 5502 (1970); http://dx.doi.org/10.1063/1.1672816 (9 pages) | Cited 43 times

Online Publication Date: 8 September 2003

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Collisional quenching of O2(b1Σg+,υ′  =  0) at room temperature by O2 and a variety of foreign gases has been investigated with a pulsed lifetime measurement technique. O2(b1Σg+,υ′  =  0) has been produced in a pulsed mode through flash photolysis of O2 in the vacuum uv and has been detected through the emission of the (0, 0) band at 7620 Å of the forbidden O2(b1Σg+ → X3Σg− transition. The (0, 0) band intensity has been measured as a function of time after the photolysis flash and as a function of the O2 and foreign gas pressures. Quenching rate constants are derived from the reactive lifetimes. The photolytic production of O2(b1Σg+,υ′  =  0) from O2 and the quenching by O2 has been studied at O2 pressures from 0.02–100 torr. The observations at low O2 pressures from 0.02 to about 1 torr are consistent with the previously established fast O2(b1Σg+) production mechanism,
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in the Schumann–Runge continuum region. No emission of the (1, 1) and (2, 2) atmospheric bands has been observed indicating that under the conditions employed, O2(b1Σg+,υ′ > 0) is either initially formed only to a relatively small degree in this mechanism or that O2(b1Σg+,υ′ > 0) is relaxed or quenched by O2 within less than 103 collisions. From the (0, 0) band fluorescence decay rates measured at O2 pressures from 0.02 to about 0.5 torr a quenching rate constant of 4.5 × 10−16 cm3 molecule−1⋅sec−1 is derived. At higher pressures, the decay rate deviates from a linear dependence on the O2 pressure indicating that the reactive lifetime is influenced by some secondary process at these pressures. The decay rate measured for example at 20 torr, O2 would correspond to a quenching coefficient of 4.8×10−17 cm3 molecule−1⋅sec−1. Quenching of O2(b1Σg+,υ′  =  0) by He, Ne, Ar, Kr, Xe, H2, N2, CO, CO2, SF6, NH3, H2O, CH4, C2H6, C2H4, NO, NO2, and N2O has been investigated by measuring reactive lifetimes at constant O2 pressures as a function of the added foreign gas pressures. Quenching rate constants are reported and compared with previous results.

Asymptotic Relations between the Thomas–Fermi–Dirac and Thomas–Fermi Atom Models. II. Extension of the Case of Low Atomic Number

R. E. Hartle and J. J. Gilvarry

J. Chem. Phys. 52, 5510 (1970); http://dx.doi.org/10.1063/1.1672817 (2 pages)

Online Publication Date: 8 September 2003

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The asymptotic relation between the pressure with exchange in the Thomas–Fermi–Dirac atom model and the corresponding pressure without exchange in the Thomas–Fermi model for the case of low atomic number considered in the first paper of this series is generalized by including a correction corresponding to the first‐order Coulomb contribution to the energy of the atom, in addition to the kinetic energy of the electrons alone. Comparison is made with numerical results obtained by direct solution of the Thomas–Fermi–Dirac equation.

Relaxation Behavior of the Freely Jointed Chain

Peter H. Verdier

J. Chem. Phys. 52, 5512 (1970); http://dx.doi.org/10.1063/1.1672818 (6 pages) | Cited 28 times

Online Publication Date: 8 September 2003

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A method is presented for treating the relaxation behavior of the freely jointed chain model of a random coil polymer. Exact results are exhibited for the relaxation of quantities linear in chain coordinates. For the treatment of quantities quadratic in chain coordinates, a numerical approach is employed and exemplified by obtaining the autocorrelation in the square of end‐to‐end length for chains of up to 16 beads. In both cases, the rapid approach of the behavior of the freely jointed chain of N beads to that of the Rouse model of N statistical segments is demonstrated.

Collision Induced Dissociation of Molecular Ions

M. H. Cheng, M. Chiang, E. A. Gislason, B. H. Mahan, C. W. Tsao, and A. S. Werner

J. Chem. Phys. 52, 5518 (1970); http://dx.doi.org/10.1063/1.1672819 (8 pages) | Cited 32 times

Online Publication Date: 8 September 2003

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Velocity vector distributions of the fragment ion products of the dissociative collisions of O2+, N2+, NO+, and N2O+ with He have been determined, using projectile‐target relative kinetic energies which are one to three times the bond energy of the molecular ion. The most probable dissociation event produces a fragment ion whose velocity is very nearly the same as that of the original projectile ion. Fragment ions also appear at smaller velocities and larger scattering angles, and the importance of these features increase with increasing initial relative energy. Three models for the dissociation are discussed, and it is concluded that a version of the stripping model is most nearly consistent with the data.

Molecular Motions in Several Solids Studied by Nuclear Magnetic Relaxation in the Rotating Frame

Stephen B. W. Roeder and D. C. Douglass

J. Chem. Phys. 52, 5525 (1970); http://dx.doi.org/10.1063/1.1672820 (6 pages) | Cited 40 times

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Rotating frame nuclear magnetic relaxation times have been measured as a function of temperature from 117 to 290°K for perfluorocyclohexane, cyclohexane, 2,2‐dichloropropane, neopentane, and tetramethylammonium iodide. The data are interpreted in terms of molecular rotation and diffusion in the solid state.

Application of an Approximate Percus–Yevick Equation for Liquid Water

A. Ben‐Naim

J. Chem. Phys. 52, 5531 (1970); http://dx.doi.org/10.1063/1.1672821 (11 pages) | Cited 20 times

Online Publication Date: 8 September 2003

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An approximate Percus–Yevick equation for liquid water is suggested. The approximation involves the splitting of the potential of average force for two particles into a sum of a direct, angle‐dependent pair potential and an angle‐independent indirect potential. The angle‐dependent pair potential is chosen in such a way that the characteristic tetrahedral geometry for the relative orientation of two water molecules is favored. Employing this potential function in the integral equation produces a pair correlation function which carries the main features of the experimental pair correlation function for liquid water.

Far‐Infrared and Raman Spectra of Phosphonium Chloride and Phosphonium Chloride‐d4

J. R. Durig, D. J. Antion, and C. B. Pate

J. Chem. Phys. 52, 5542 (1970); http://dx.doi.org/10.1063/1.1672822 (7 pages) | Cited 2 times

Online Publication Date: 8 September 2003

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The far‐infrared spectra of thin films of PH4Cl and PD3Cl have been recorded at −170°C. Raman spectra of polycrystalline samples of both compounds were also recorded at −170°C. One libration and three translations were observed as well as eight internal modes. Several combinations and overtones were assigned and the zone‐edge wavenumber of a second libration has been inferred. The barrier restricting re‐orientation of the PH4 and PD4 ions has been calculated from the observed librational wavenumbers to be 8.5 kcal/mole and forces contributing to the barrier are discussed. The lattice dimensions of PH4Cl were determined to be a  =  b  =  5.82Å and c  =  4.22Å from the x‐ray diffraction pattern of a polycrystalline sample.

Electron Paramagnetic Resonance of (Agpy2)2+ in Nitric Solution at 77°K

T. Halpern, W. D. Phillips, and J. A. McMillan

J. Chem. Phys. 52, 5548 (1970); http://dx.doi.org/10.1063/1.1672823 (3 pages) | Cited 5 times

Online Publication Date: 8 September 2003

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The paramagnetic resonance spectrum of (Agpy2)2+ in frozen nitric solution has been observed at 77°K. It exhibits silver hyperfine as well as superhyperfine structure, this latter due to interaction with two equivalent nitrogen nuclei. Due to a strong axial g anisotropy the principal values of the hyperfine and superhyperfine interaction tensors may be determined. Wavefunctions are calculated for the unpaired electron as well as its density in the metal ion and the ligands. The experimental values are consistent with the picture of a hole in the Ag d shell in an oblate tetragonal octahedron, which is partially transferred to an sp4 nitrogen hybrid. Coefficients for the wavefunctions are given and the ring C☒N☒C angle found in reasonable agreement with independently estimated values.
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Comments on the Analysis of Atomic Correlation Energies

John Gruninger, Yngve öhrn, and Per‐Olov Löwdin

J. Chem. Phys. 52, 5551 (1970); http://dx.doi.org/10.1063/1.1672824 (4 pages) | Cited 12 times

Online Publication Date: 8 September 2003

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Analysis of correlation energies is advocated in terms of average values of electronic kinetic energy, electron–nuclear attraction energy, and electron–electron repulsion energy, rather than pair energies. Exploratory calculations on the two‐electron and three‐electron isoelectronic sequences are reported.

Ethereal Electrons

Sivert H. Glarum and James H. Marshall

J. Chem. Phys. 52, 5555 (1970); http://dx.doi.org/10.1063/1.1672825 (11 pages) | Cited 39 times

Online Publication Date: 8 September 2003

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Solutions of K, Rb, and Cs in dimethoxyethane consist primarily of metal cations and anions. The latter are ionized by light at wavelengths between 700 and 1000 nm to yield solvated electrons. Electron recombination occurs by a second‐order mechanism involving an M⋅species, and rate constants have been estimated from ESR data. Photoelectrons emitted from Rb− are highly polarized, and an explanation combining spin–orbit and exchange interactions with an adiabatic dissociation is proposed.

Induction Forces. An Exact Treatment of Charge Overlap Effects through Third Order

T. R. Singh, H. Kreek, and William J. Meath

J. Chem. Phys. 52, 5565 (1970); http://dx.doi.org/10.1063/1.1672826 (7 pages) | Cited 36 times

Online Publication Date: 8 September 2003

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The interaction of a ground‐state atom or ion, consisting of a nucleus and a single electron, with a charge is considered in detail as a model for discussing induction forces through third order in the interaction potential. Expressions for all the angular components of the first‐order wavefunction and for all the individual nonexpanded second‐order induction energies are given in closed form. Exact numerical values for the total third‐order induction energy and its individual nonexpanded components, through terms varying as R−11 at long range, are given in tabular form for the H☒H+ interaction. The results are discussed with emphasis on the effects of charge overlap on induction forces through third order and on the complicated structure of the third‐order energy in terms of its individual nonexpanded induction energies. In the Appendix the Green function approach to the problem is discussed with the relevant Green functions being obtained as solutions of differential equations rather than by direct summation of their spectral expansions.

Adsorption of Inert Gases on Tungsten: Measurements on Single Crystal Planes

T. Engel and R. Gomer

J. Chem. Phys. 52, 5572 (1970); http://dx.doi.org/10.1063/1.1672827 (9 pages) | Cited 83 times

Online Publication Date: 8 September 2003

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The adsorption of Ar, Kr, and Xe on the (110), (120), (100), (211), and (111) planes of a tungsten field emitter was studied under conditions of immobile adsorption and also under conditions of surface equilibrium. The relative dipole moments and heats of binding could be determined, and it was found that both these quantities were largest on the (110) plane. A discussion in terms of charge transfer bonding is presented to rationalize these results. It was found that chemisorption of oxygen prevented the relatively strong first layer adsorption observed on the clean surface, and also the dipole moment associated with it.

Simple and Accurate Approximation for the Centrifugal Factor in RRKM Theory

E. V. Waage and B. S. Rabinovitch

J. Chem. Phys. 52, 5581 (1970); http://dx.doi.org/10.1063/1.1672828 (4 pages) | Cited 15 times

Online Publication Date: 8 September 2003

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An approximate form for the low pressure centrifugal effect is derived for RRKM unimolecular rate theory calculations. Comparisons are made with earlier approximations and with a more exact result. The effects on the observed activation energy and extension to the region of falloff are described.

Effect of Ion Pairing on the g Value of the Naphthalene Anion Radical

W. Gavin Williams, Roger J. Pritchett, and George K. Fraenkel

J. Chem. Phys. 52, 5584 (1970); http://dx.doi.org/10.1063/1.1672829 (12 pages) | Cited 10 times

Online Publication Date: 8 September 2003

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Measurements have been made of the g values of the naphthalene radical anion associated with several alkali‐metal cations at a series of temperatures and in different solvents. It has been suggested previously that the temperature dependences of the g factors of spectra exhibiting alkali‐metal splittings can be explained either in terms of equilibrium changes between two paired species (Hirota model) or in terms of changes in the populations of the vibrational energy levels of a paired species of fixed electronic structure (Atherton–Weissman model). Evidence is presented to show that the Hirota model adequately accounts for the g‐factor variations of the sodium naphthalenide ion pair in tetrahydrofuran, but not for the cesium naphthalenide ion pair in 1,2‐dimethoxyethane. It is argued that the latter ion pair is probably a tight ion pair which does not incorporate solvent molecules, and that the variations of the spectral parameters of such complexes are best described by the Atherton–Weissman model.

Theory of the Hyperfine Splittings of Pi‐Electron Free Radicals. III. Methyl Radical in a Pyramidal Configuration: Temperature Dependence of the Hyperfine Splittings

S. Y. Chang, E. R. Davidson, and G. Vincow

J. Chem. Phys. 52, 5596 (1970); http://dx.doi.org/10.1063/1.1672830 (11 pages) | Cited 26 times

Online Publication Date: 8 September 2003

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Nonempirical calculations for methyl radical (CH3⋅) in a pyramidal configuration (C3υ) were performed using two minimum basis sets of Slater‐type orbitals, one in which orbital exponents were chosen according to Slater's rules (unoptimized) and the other in which they were optimized by minimization of the SCF energy. The spin‐restricted SCF plus configuration‐interaction method, including all spin‐adapted configurations with single and double excitations of space orbitals, was employed. The temperature dependence of the contact hyperfine splittings was computed assuming that the variation with temperature arises from the out‐of‐plane bending motion. Agreement with experiment at various temperatures is good. The optimized‐basis values of the temperature coefficient of the proton splitting, daH / dT, are about 20%–50% too large and the unoptimized‐basis results are about 10%–25% too small. Temperature coefficients of the carbon‐13 splitting calculated using the optimized and unoptimized basis sets also bracket the experimental values, from which they deviate by less than 10%, which is within the experimental uncertainty. The variation of the spin densities at the magnetic nuclei with the out‐of‐plane angle is analyzed in detail. Other results of the calculation are discussed, namely, the equilibrium molecular geometry, an approximate frequency for the bending motion, and the incomplete orbital following.

Crystal Structure of Luminescent ZnSiP2

S. C. Abrahams and J. L. Bernstein

J. Chem. Phys. 52, 5607 (1970); http://dx.doi.org/10.1063/1.1672831 (7 pages) | Cited 51 times

Online Publication Date: 8 September 2003

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ZnSiP2 crystallizes with the chalcopyrite structure: there is no detectable difference in x‐ray scattering between luminescent and nonluminescent crystals. The level of impurity, either in the form of chemical dopant, physical defect, or a departure of less than about 1% from complete order at the Zn and Si sites hence determines if the crystal luminesces or not on excitation by an electron beam. The lattice constants of this tetragonal crystal at 298°K are a  =  5.399 ± 0.001 and c  =  10.435 ± 0.002Å. The space group is Imath2d, and there are four formulas in the unit cell. A total of 2023 reflections were measured with the luminescent crystal, and 1600 with the nonluminescent crystal, using pexrad. The final agreement factor, based on a combination of 197 symmetry‐independent reflections from the first crystal and 176 from the second, is 0.049. Each Zn is tetrahedrally surrounded by 4 P atoms at 2.375 ± 0.001 Å distance, and each Si by 4 P atoms at 2.254 ± 0.001 Å. All phosphorus tetrahedra have four P☒P edges of length 3.832 ± 0.002 Å. The two remaining independent P☒P edges are of 3.968 ± 0.001 Å distance in the ZnP4 tetrahedra, and are of 3.684 ± 0.001 Å in the SiP4 tetrahedra.

Dipole Moment of the First Excited π* ← π State of Fluorobenzene

Kwo‐Tsair Huang and John R. Lombardi

J. Chem. Phys. 52, 5613 (1970); http://dx.doi.org/10.1063/1.1672832 (3 pages) | Cited 12 times

Online Publication Date: 8 September 2003

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A Stark effect is observed in the rotational fine structure of the 0–0 band of the lowest‐lying singlet π* ← π state of fluorobenzene. Splittings are found in both P and R branches. This enables us to determine the excited‐state dipole moment to be μ′  =  1.96 ± 0.07D. This result is discussed in relation to previous measurements on substituted benzenes, and it is shown that the previously observed correlation between structure and dipole moment for excited states also extends to fluorobenzene.

Identifying the Lowest Excited Singlet State of Biphenyl and Its Analogs

Isadore B. Berlman

J. Chem. Phys. 52, 5616 (1970); http://dx.doi.org/10.1063/1.1672833 (6 pages) | Cited 49 times

Online Publication Date: 8 September 2003

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From experimental evidence it is inferred that the broad structureless absorption band of biphenyl at about 2500 Å is composed of bands from three transitions, a weak transition similar to the 1A → 1Lb transition of benzene and two stronger transitions similar to the 1A → 1La and 1A → 1B transitions of benzene. Bands from these transitions are separated in rigid biphenyl analogs such as 9,10‐dihydrophenanthrene and fluorene. Certain fluorescence characteristics of biphenyl (such as decay time τ and quantum yield Q) are distinctive of the weak and “hidden” transition and a dramatic change in these characteristics is observed when a crossover of the two lowest excited states is achieved in the analogs of biphenyl. Specific substituents, when positioned in the para position (such as a phenyl or vinyl group in p‐terphenyl or 4‐vinylbiphenyl, respectively), are particularly efficacious in producing a crossover of levels. In these cases, the lowest excited state is an allowed transition similar to one component of the degenerate 1A → 1B transition in benzene. Since the intense absorption bands are maximally shifted by substituents on the para position, the transition moment must be long‐axis polarized as predicted theoretically. Bridging is particularly effective in producing a bathochromic shift because the phenyl rings can be constrained to lie in a relatively coplanar and linear configuration. The magnitude of the shift imparted to the various states depends on the bridging element. From the value of the ratio τ / Q, the assignment of the lowest excited singlet state can be determined: In fluorene, dibenzofuran, and 9,10‐dihydrophenanthrene, it is 1La; in carbazole and phenanthrene, 1Lb; and in 2‐phenylfluorene and 2‐phenyl‐9,2′‐methylenefluorene, 1Bb.

Elementary Model of the Broadening of Localized Transitions in a Simple Liquid

William L. Greer, Stuart A. Rice, and Graeme Morris

J. Chem. Phys. 52, 5622 (1970); http://dx.doi.org/10.1063/1.1672834 (6 pages) | Cited 1 time

Online Publication Date: 8 September 2003

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The line shapes corresponding to localized electronic or vibrational transitions in a simple liquid are studied using a model. The model is defined by a Hamiltonian taken to be linear in the instantaneous force acting on a molecule. One consequence of this assumption is the appearance of the force autocorrelation function in the line‐shape formulas. It is shown that in the weak coupling limit, in the lowest order of approximation, the transition line shape is Lorentzian. In the next approximation the line shape has a frequency dependence given by the convolution of the lowest‐order Lorentzian with the frequency‐dependent force autocorrelation function. Some implications of the model are discussed, and a rationalization given to interpret variations in the line shapes of Raman transitions corresponding to totally symmetric and nontotally symmetric vibrations.

Molecular Zeeman Effect of Trimethylene Oxide and Trimethylene Sulfide

R. C. Benson, H. L. Tigelaar, S. L. Rock, and W. H. Flygare

J. Chem. Phys. 52, 5628 (1970); http://dx.doi.org/10.1063/1.1672835 (8 pages) | Cited 7 times

Online Publication Date: 8 September 2003

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The rotational Zeeman effect has been observed in trimethylene oxide and trimethylene sulfide. The molecular g values, magnetic susceptibility anisotropies, and molecular quadrupole moments were obtained for both molecules. The a and b axes are in the molecular plane and the a axis bisects the COC or CSC angle. The magnetic susceptibility values are given below in units of 10−6 erg/G2⋅mole, and the molecular quadrupole moments are in units of 10−26 esu⋅cm2. The results for trimethylene oxide are: gaa  =  − 0.0073 ± 0.0005,gbb  =  − 0.0429 ± 0.0007, and gcc  =  − 0.0747 ± 0.0005;2χaa − χbb − χcc  =  − 20.1 ± 0.5 and − χaa + 2χbb − χcc  =  − 13.5 ± 0.8;Qaa  =  − 4.9 ± 0.5,Qbb  =  + 2.3 ± 0.7, and Qcc  =  + 2.6 ± 1.0. A reliable value of the average magnetic susceptibility in ethylene oxide is also given. The results for trimethylene sulfide are: gaa  =  − 0.0148 ± 0.0010,gbb  =  − 0.0169 ± 0.0006,gcc  =  − 0.0554 ± 0.0005;2χaa − χbb − χcc  =  − 20.9 ± 1.0 and − χaa + 2χbb − χcc  =  − 24.6 ± 1.0;Qaa  =  − 2.7 ± 1.0,Qbb  =  + 3.2 ± 1.0, and Qcc  =  − 0.5 ± 1.6. Due to the large vibration–rotation interaction in trimethylene sulfide, it was found that consistent g values could be obtained only when this interaction was included in the analysis. The results are compared with previously measured oxygen‐ and sulfur‐containing molecules.

Molecular g Values, Magnetic Susceptibility Anisotropies, Second Moments of the Electronic Charge Distribution, and Molecular Quadrupole Moments in Pyridine

J. H. S. Wang and W. H. Flygare

J. Chem. Phys. 52, 5636 (1970); http://dx.doi.org/10.1063/1.1672836 (5 pages) | Cited 26 times

Online Publication Date: 8 September 2003

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The high‐field linear and quadratic Zeeman effect has been observed in pyridine. The spectra is complicated by the presence of the 14N nuclear quadrupole coupling. Perturbation theory through second order is used to extract the molecular Zeeman parameters. The molecular g values are gaa  =  − (0.0770 ± 0.0005),gbb  =  − (0.1010 ± 0.0008), and gcc  =  0.0428 ± 0.0004. The magnetic susceptibility anisotropies are (2χaa − χbb − χcc)  =  (54.3 ± 0.6) × 10−6 and (2χbb − χaa − χcc)  =  (60.5 ± 0.8) × 10−6 in units of erg/gauss2⋅mole. The a axis bisects the CNC angle and the b axis is also in the molecular plane. The molecular quadrupole moments are Qaa  =  − (3.5 ± 0.9),Qbb  =  9.7 ± 1.1,Qcc  =  − (6.2 ± 1.5) all in units of 10−26 esu⋅cm2. Using the known molecular structure and the molecular g values gives the diagonal elements in the paramagnetic susceptibility tensor and the anisotropies in the second moment of the electronic charge distribution. These results are χaap  =  241.5 ± 1.5,χbbp  =  247.4 ± 2.0, and χccp  =  393.9 ± 2.0 all in units of 10−6 erg/G2⋅mole and 〈a2〉 − 〈b2〉  =  0.92 ± 0.80, 〈b2〉 − 〈c2〉  =  48.28 ± 0.60, and 〈c2〉 − 〈a2〉  =  − 49.19 ± 0.60 all in units of 10−16 cm2. Combining the above values with the known bulk magnetic susceptibility gives the individual diagonal elements in the total and diamagnetic susceptibility ternsors. The individual values of 〈a2〉,〈b2〉, and 〈c2〉 are also obtained. The results are compared to other ring compounds.

Lyman‐α Fluorescence from the Photodissociation of H2

J. E. Mentall and E. P. Gentieu

J. Chem. Phys. 52, 5641 (1970); http://dx.doi.org/10.1063/1.1672837 (5 pages) | Cited 47 times

Online Publication Date: 8 September 2003

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Photodissociation and fluorescence cross sections for H2 have been measured from 860 to 700 Å by observing the Lyman‐α photons emitted at 90° to an incident photon beam. The photodissociation quantum efficiency was found to be unity from 850 Å to the photoionization threshold at 804 Å and about 10% at shorter wavelengths. By observing the fluorescence radiation as a function of decreasing pressure, it was determined that most of the excited H atoms were formed in the metastable 2s state and that the Lyman‐α emission results primarily from collisional quenching. The ratio of the collisional cross section with and without Lyman‐α emission was measured for different relative velocities and was found to increase appreciably with increasing velocity.

Raman Spectra and Force Constants for OsO4 and XeO4

John L. Huston and Howard H. Claassen

J. Chem. Phys. 52, 5646 (1970); http://dx.doi.org/10.1063/1.1672838 (3 pages) | Cited 17 times

Online Publication Date: 8 September 2003

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Raman spectra are presented for OsO4 vapor, and for XeO4 vapor and solid. Observed fundamental frequencies (in cm−1) for gaseous OsO4 are 965.2(a1),333.1(e),960.1(f2), and 322.7(f2). For XeO4 they are 773(a1) for the vapor, and 767.1(a1),277(e),867(f2), and 303‐f2) for the solid. The Urey–Bradley constant F is 0.32 for OsO4, and −0.18 mdyn/Å for XeO4.

Dynamic Nuclear Polarization in Phosphorus Compounds with Perchlorotriphenylmethyl and Other Radicals

Edward H. Poindexter and George R. Neil

J. Chem. Phys. 52, 5648 (1970); http://dx.doi.org/10.1063/1.1672839 (4 pages) | Cited 4 times

Online Publication Date: 8 September 2003

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Dynamic nuclear polarization has been examined in liquid solutions containing the radical perchlorotriphenylmethyl and 14 different phosphorus compounds. In addition, the radicals bisdiphenylenephenylallyl, tri‐t‐butylphenoxyl, and diphenylpicrylhydrazyl have been examined with five phosphorus compounds. The chlorocarbon radical shows on the average the least scalar coupling of the four. This is in accord with the well‐shielded spin distribution on this radical and the great chemical stability of aromatic chlorocarbons. PCTM is found to be almost completely inert, both electronically and chemically, toward phosphines and phosphites. Exceptional cases of high coupling were observed with PCTM and dimethylphosphite, triphenylphosphine oxide, and hexamethylphosphoramide. The first case appears to be due to a transient hydrogen bond Cl⋅⋅⋅H☒P, the second due to an exposed polarizable orbital system, and the last due to an obscure chemical complexation tendency. Exceptional cases with the other radicals serve to illustrate further stereospecific molecular couplings between sites of active chemical or electronic attraction for each other.
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