Volume 36, Issue 5, 01 March 1962
Index of content:
36(1962); http://dx.doi.org/10.1063/1.1732702View Description Hide Description
The microwave spectrum and structure of sulfur tetrafluoride has been determined. One FSF angle is 101°33′±30′, the opposite FSF angle is 186°56′±30′. The bond length for the nearly linear bonds is 1.646 A±0.003 A; for the other pair it is 1.545 A±0.003 A. The dipole moment was determined from the Stark effect to be 0.632±0.003 debye.
36(1962); http://dx.doi.org/10.1063/1.1732703View Description Hide Description
Deuteron magnetic resonance spectra were observed in ND4Cl, ND4Br, ND4ClO4, ND4BF4, ND4IO3, and (ND4)2SO4 in their powder form. Absorption patterns characteristic of the rapid reorientation of ND4 + ions were obtained. For the first four compounds, the absorption line consists of a sharp single line; for the remaining two it has structure which is due to small quadrupole coupling. For (ND4)2SO4, the angular dependence of the resonance pattern was measured with a single crystal specimen. The following values of the quadrupole coupling constant and asymmetry parameter were obtained:andThe results of the experiment were discussed in relation to the crystal structure, crystalline field effect, and the deformation of ND4 + ion in the crystal. It was concluded that the observed quadrupole coupling for ammonium sulfate is mainly due to a direct effect of the distortion of the ammonium ion in the crystal rather than to the crystalline field effect. The observed asymmetry parameter for ammonium iodate did not agree with the reported crystal structure.
Studies in Molecular Structure. VII. Limited Configuration Interaction for Selected First‐Row Diatomics36(1962); http://dx.doi.org/10.1063/1.1732704View Description Hide Description
Calculations on selected first‐row diatomic molecules using a limited configuration interaction with minimal LCAO MO SCF wave functions are described. Molecular energies, dipole moments, and population analyses are tabulated and discussed. These results provide an extensive foundation for a tentative evaluation of the value of limited configuration interaction for LiH, BH, NH (d 1Σ+), HF, Li2, C2, N2, F2, LiF, CO, and BF within the limits of the approximations used.
36(1962); http://dx.doi.org/10.1063/1.1732705View Description Hide Description
The electron spin resonance spectra of an irradiatedsingle crystal of DL‐tartaric acidgrown from water was found to be complex, but the spectra of a deuterated single crystal could be analyzed and the nature of the free radical ascertained. Measurements were made at 9 and at 23 kMc/sec. For some orientations of the crystal in the external magnetic field an unresolved doublet was observed with weak satellite lines separated by 5 gauss at 9 kMc/sec and by 13 gauss at 23 kMc/sec. These satellite lines evidently arise from second‐order transitions. From the analysis we suggest that the free radical is probably[Complex chemical formula]with the unpaired spin on a carbon atom. The principal values of g are 2.0025, 2.0026, and 2.0047. The principal elements of the nuclear coupling of the CH protons are ∓0.2, ±1.1, and ±6.5 gauss.
36(1962); http://dx.doi.org/10.1063/1.1732706View Description Hide Description
The decomposition of gaseous BrCN in shock waves has been measured over the temperature range 2500–7000°K by following the light emitted by CN and C2. The rate of the reaction in 1 and 5% mixtures with Ar is —d[BrCN]/dt=2.0×1012 T ½ exp (—90.5 kcal mole—1/RT) [Ar] [BrCN] mole cc—1 sec—1. The subsequent disappearance of CN as determined by both the loss of CN and the formation of C2 is consistent with the reaction 2CN→C2+N2 for which the bimolecular rate constant is 1.6×1015 exp (—43 kcal mole—1/RT) cc mole—1 sec—1.
36(1962); http://dx.doi.org/10.1063/1.1732707View Description Hide Description
The visible absorption spectra of the ions [Fe(CN)5NO]2—, [Mn(CN)5NO]3—, and [Cr(CN)5NO]3— are interpreted using a crystal field level scheme of C 4v symmetry. Assuming a strong axial compression to be present a self‐consistent assignment is obtained for both the 3d 5 and 3d 6 electronic configurations.
36(1962); http://dx.doi.org/10.1063/1.1732708View Description Hide Description
Previous calculations of the H–H coupling in CH2 groups assumed a static H–C–H bond angle. It is shown here that, because the predicted angular dependence of the coupling is nonlinear, the bond‐bending vibrations should give an averaged value appreciably larger than that for the corresponding equilibrium, but static, angle. The contribution of excited vibrational states is very small and hence the averaged coupling constant is effectively temperature independent. There should be a small but detectable difference in the coupling constants for CH2 and CHD groups because of the isotopic differences in vibrational amplitude. The experimental coupling constants exhibit an apparent linear dependence upon the equilibrium H–C–H angle, and careful measurements of the isotope effects could be useful in establishing whether or not there is any explicit curvature in the angular dependence, and thus whether the observed linearity is real or due to the neglect of substituent effects in the calculations. In any case, comparison between experiment and the predicted angular dependence suggests that too low a value may have been used previously for one of the exchange integrals, K(C 1, C 2) in the calculations for both the CH2 and the HCCH groups. An attempt to detect an isotopic difference between the geminal H–F and D–F coupling in n—C3F7H and n—C3F7D gave negative results.
36(1962); http://dx.doi.org/10.1063/1.1732709View Description Hide Description
Vibronic coupling between the doubly degenerate orbital of the odd electron and the in‐plane antisymmetric stretching vibration of the C–C bonds in C8H8 — radical leads to two ground states of equal energy if the radical is planar. They correspond to vibrations about either of two equivalent distorted structures with alternating double and single bonds. The potential barrier between these structures has been estimated to be 824 cm—1. We find that the barrier considerably damps the fluctuations of electron charge and spin density which would occur in the undistorted planar radical. This situation is to be contrasted with benzene negative ion, in which vibronic coupling involved a degenerate vibration, and for which large undamped fluctuations have been anticipated on the basis of a similar theoretical description. This conclusion agrees with the recent observation of considerably narrower lines in the electron spin resonance spectra of C8H8 — than were reported by Townsend and Weissman for spectra of the benzene and coronene negative ions.
Theoretical Investigations on the Light Scattering of Spheres. XIII. The ``Wavelength Exponent'' of Differential Turbidity Spectra36(1962); http://dx.doi.org/10.1063/1.1732710View Description Hide Description
The exact theory of the ``wavelength exponent'' of the turbidity is developed for Rayleigh scattering and ``Debye scattering'' and, particularly, for Mie scattering by nonabsorbing spheres. The basic exponent, n, defined by is computed from Mie turbidity data, reported previously, for α=0.40 (0.04) 0.68, 0.80 (0.2) 25.0 and m=1.05 (0.05) 1.20. For m=1.25 and 1.30, the smallest α values and the Δα intervals are the same, but the upper limiting α values are 14.0 and 11.6, respectively. In addition, α values<0.40 are considered for m=1.05. The actual exponent to be expected in a given dispersed systemn 0 is found to depend on three additional factors: (1) The rate of change of the turbidity with the relative refractive index of the spheres [this factor is evaluated for α=0.4, 1.0 (1.0) 7.0 and m=1.05 (0.05) 1.30 and approximating equations are given for purposes of interpolation]. (2) The dispersion of the relative refractive index of the spheres. (3) That of the refractive index of the medium. The advantages and limitations of an application of the wavelength exponent to particle size determinations are discussed and labor saving approximating n(α) relations, suitable for first approximation results on particle size, are given. The effect of heterodispersion upon the wave length exponent is briefly discussed.
36(1962); http://dx.doi.org/10.1063/1.1732711View Description Hide Description
The energetics of the interactions of N2 and CO with initially clean tungstensurfaces are analyzed to establish the dependence of chemisorption upon surface structure. For N2, calorimetric measurements yield a heat of adsorption of ∼90 kcal mole—1, constant over the range of coverages accessible at T=300°K. This suggests that the equilibrium binding sites for nitrogen are energetically equivalent. Desorption obeys bimolecular kinetics, with an activation energy of ∼81 kcal mole—1, unchanging to the highest surface concentrations (n∼250×1012 molecules cm—2).
This constancy confirms the energetic equivalence of the surface sites filled by nitrogen, and demonstrates the presence of adatoms without lateral interactions. Alternative proposals for the occupation of binding sites of different strengths are examined and rejected as caused by experimental error.
In contrast, evolution of CO takes place in distinct steps, with activation energies of 53, 75, and ∼100 kcal mole—1 for β material. Stepwise desorption stems from the arrangement of CO binding sites. These differ in strength, are widely separated from one another, and presumably consist of planes with different crystallographic orientation.
Despite the constant heat of adsorption, the presence of an activation barrier to surfacediffusion, amounting to ∼35 kcal mole—1 on the approaches to the (100), demonstrates that binding of nitrogen atoms does depend on surface structure. In the regions between equilibrium sites, a nitrogen adatom is less firmly bound. On the (110) planes, in which each tungsten atom has six nearest neighbors, the binding energy of a nitrogen adatom is lowered to such an extent that at room temperature these areas should be bare. This is confirmed by direct observation in the field ion microscope. Such ``structural exclusion'' arises from the high dissociation energy of N2, which precludes occupation of sites accessible to other, less strongly bonded molecules. For nitrogen atoms only a narrow band in the total spectrum of binding energies is available. Structural exclusion is also shown to be in accord with the following unique properties of nitrogen layers: (1) The limited concentration (∼40% of the total number of surface sites) achievable at room temperature; (2) The presence of an additional and heavily populated binding state (γ) at T<200°K; (3) The absence of interactions between adatoms.
36(1962); http://dx.doi.org/10.1063/1.1732712View Description Hide Description
The electronic structure of NO2 and related molecules is discussed by means of a correlation diagram between the molecular orbitals of O3 and CO2. The general properties of the hyperfine structure constants for the different kinds of orbitals are discussed and compared with the experimental results of NO2 and ClO2. The hyperfine structure constants are used to identify the symmetry properties of the ground states of NO2 and ClO2 and also to estimate some coefficients of the atomic orbitals in the LCAO MO.
36(1962); http://dx.doi.org/10.1063/1.1732713View Description Hide Description
The theoretical shapes of the potential curves for bond alternation in ground and excited states in cyclic polyenes are given. It is shown that the current MO model tends to give a rather small barrier to tunneling between the two alternating nuclear configurations, and that the barrier disappears in the excited states. If the potential curves do differ between ground and excited states, peculiar progressions should appear in the spectrum. An analysis is presented of the low‐temperature spectrum of C18H18 that shows no such effect. It is suggested that the success that bond alternation has had in interpreting various phenomena is due to the fact that it makes the electrons less free than current models would have, but that this effect may stem from other subtler causes.
36(1962); http://dx.doi.org/10.1063/1.1732714View Description Hide Description
Crystalline solids have been prepared from aromatic hydrocarbons and tetrahalogenated benzoquinones. The solids contain one molecule of hydrocarbon for every molecule of quinone. The infrared and optical spectra of the solids, as well as their chemical properties, indicate that the components are bound by electronic donor‐acceptor interactions which are weak compared to the intramolecular forces.
Electron spin resonance absorption at 9500 Mc/sec was observed in nearly all the hydrocarbon‐quinone solids prepared. However, perylene‐quinone solids have been prepared which contain less than 1015 unpaired electron spins per gram. That is, they are practically diamagnetic. When unpaired electrons are present they are located at imperfections in the solid. Imperfections containing unpaired electron spins can be introduced thermally into the complexes. More than 1018 unpaired electrons per gram can be produced by heating perylene‐ortho‐quinone solids.
The temperature dependences, g values, linewidths and spin‐lattice relaxation times of the electron spin resonance absorption by the imperfection in some perylene‐quinone solids have been investigated. The structure of the imperfection and the mechanism by which it is produced have been discussed.
36(1962); http://dx.doi.org/10.1063/1.1732715View Description Hide Description
The polarized infrared absorption spectra of single crystals of K3Co(CN)6 have been observed from 5000 to 280 cm—1. By combining this data with Raman and crystal structure data of other authors, most of the fundamental frequencies have been assigned. Force constants have been calculated using the recently derived resonance interaction valence force potential function which reduces the number of interaction terms in accord with theories of bonding. The primary stretching force constants are: F CN=16.8 md/A and F CoC=1.8 md/A.
It is shown that the observed spectrum cannot be satisfactorily explained with a Urey‐Bradley force field.
36(1962); http://dx.doi.org/10.1063/1.1732716View Description Hide Description
The nuclear magnetic resonance spectra of Na23 and Al27 in a single crystal of natrolite (Na2Al2Si3O10·2H2O), a fibrous zeolite, have been investigated at room temperature in an external magnetic field of 7380 gauss. It was found that the sodium and aluminum atoms each occupy a single chemically unique site in the unit cell. The quadrupole coupling constants and asymmetry parameters of the electric field gradient tensors at these sites were determined to beThe orientations of the principal axes of the electric field gradient tensors for the above sites and their symmetry‐related sites have also been determined.
Some Studies on Argon, Helium, and Carbon Dioxide with an Integrated‐Schlieren Instrumented Shock Tube36(1962); http://dx.doi.org/10.1063/1.1732717View Description Hide Description
Using integrated‐schlieren instrumentation, an investigation has been made of shock waves in argon, helium, and carbon dioxide. In argon and helium a residual signal has been observed, which is ascribed to curvature of the shock front in the vicinity of the wall. A discussion is presented of the way in which the curved shock satisfies the boundary conditions, and of the resulting flow pattern, which includes a ``pressure adjustment region.'' Preliminary measurements on the variation of the apparent ``zone thickness'' with density and shock speed in these gases are reported. The importance of the observed shock curvature in measurements of the vibrational relaxation time for gases like carbon dioxide is considered. Preliminary results for the vibrational relaxation times of dry CO2 are reported for temperatures up to about 900°K, and are compared with results obtained by others.
36(1962); http://dx.doi.org/10.1063/1.1732718View Description Hide Description
Electrical resistancemeasurements of gas‐charged alpha hydrogen‐palladium alloys have been made in the range 100° to 400°C. The fractional increase of palladiumresistance caused by addition of hydrogen is proportional to hydrogen concentration. The constant of proportionality is independent of temperature, indicating that Matthiessen's rule is inapplicable to this system. When the results of this work are combined with those of previous authors, all of the data can be adequately represented in the range 75° to 400°C by the equation (R/R 0) — 1 = (2.41±0.04) m, where R is the resistance of alpha hydrogen‐palladium, R 0 is the resistance of hydrogen‐free palladium, and m is the hydrogen‐to‐palladium atom ratio.
36(1962); http://dx.doi.org/10.1063/1.1732719View Description Hide Description
An absolute measurement of the self‐diffusion coefficient D 11 in hydrogen gas has been made at 78°K and 117 Amagats. Relative measurements have been made of D 11 as a function of gas density at 55°, 78°, and 90°K, up to a maximum density of 650 Amagats. The experimental results are compared with viscosity data and with the theories of Buckingham and Mason. The observed density dependence of D 11 is in marked disagreement with the Enskog dense‐gas theory.
36(1962); http://dx.doi.org/10.1063/1.1732720View Description Hide Description
A study has been made with a mass spectrometer of the ionization efficiencies of a number of gases, using an ion source incorporating an electron velocity selector. It is found that the shapes of the I.E. curves are affected by numerous instrumental factors. These have been examined, and the data lead to the following conclusions. Ions may be formed on the walls of the ionization source, at energies different from those corresponding to the ionized states of the free molecules. Charge transferreactions may occur between these bound ions, and other neutral molecules on the walls. The surface ions may subsequently become detached, and are detected at the collector of the mass spectrometer.
It is suggested that these ions formed by such processes may account for many of the spurious ``breaks'' often found in measured I.E. curves. The sharpness of the structure in the present curves indicates that the half‐width of the electron energy spread is of the order of 0.02 ev.
36(1962); http://dx.doi.org/10.1063/1.1732721View Description Hide Description
The microwave spectra of C13H3CH2Cl35, CH3C13H2Cl35, CH3CD2Cl35, and CH2DCH2Cl35 have been examined and rotational constants assigned. Both a‐type and b‐type spectra have been observed. From these spectra and those previously reported for CH3CH2Cl35, CH3CH2Cl37, and CH2DCH2Cl35 a complete structure has been obtained by means of the substitution method. The bond distances and bond angles obtained are as follows: CC = 1.520 A, CCl = 1.788 A, CH (methyl) = 1.091 A, CH (methylene) = 1.089 A, CCCl = 111°2′, HCH (methyl) = 108°30′, HCH (methylene) = 109°12′, CCH (methylene) = 111°36′. The quadrupole coupling parameters and barrier to internal rotation have been re‐evaluated in terms of the above structure. The quadrupole coupling parameters are χbond = —68.80 Mc and ηbond = 0.035, if the angle between the a axis and the CCl bond is determined from the structure; or χbond = —71.24 Mc, if a cylindrical charge distribution is assumed near the chlorine nucleus. The barrier to internal rotation is 3685 cal/mole.