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15 Jun 1963

Volume 38, Issue 12, pp. 2791-3039

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Electron‐Density Distributions in Hydride Molecules. The Ammonia Molecule

R. F. W. Bader and G. A. Jones

J. Chem. Phys. 38, 2791 (1963); http://dx.doi.org/10.1063/1.1733604 (12 pages) | Cited 26 times

Online Publication Date: 20 July 2004

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An electron‐density distribution is determined for the ammonia molecule in its equilibrium configuration by requiring the distribution to exert forces on the nuclei equal and opposite to the nuclear forces of repulsion. The density distribution so obtained is compared with those determined by SCF calculations. All of the density functions are tested by comparing the calculated and observed values for the following molecular properties: (i) the forces on the nuclei, (ii) the dipole moment, (iii) the electric‐field gradient at the nitrogen nucleus, (iv) the diamagnetic susceptibility, and (v) the diamagnetic contribution to the nuclear shielding constant.

Theory of Carbon NMR Chemical Shifts in Conjugated Molecules

M. Karplus and J. A. Pople

J. Chem. Phys. 38, 2803 (1963); http://dx.doi.org/10.1063/1.1733605 (5 pages) | Cited 246 times

Online Publication Date: 20 July 2004

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A molecular orbital theory for carbon‐13 chemical shifts in conjugated molecules is formulated. Consideration of the various possible contributions to the shift shows that the local paramagnetic term σpAA is expected to dominate. By a detailed LCAO analysis of σpAA, its variation with the salient features of the electron environment is determined. It is demonstrated that there is a significant local‐charge dependence which agrees in sign and order of magnitude with an experimentally established correlation. In addition, the shielding is shown to be a function of the free valence of the atom under consideration and of the polarity of its sigma bonds. A linearized equation for the carbon‐13 chemical shift (with respect to benzene) is presented and compared with the available experimental data.

Structure of Hexagonal Silver Iodide

G. Burley

J. Chem. Phys. 38, 2807 (1963); http://dx.doi.org/10.1063/1.1733606 (6 pages) | Cited 42 times

Online Publication Date: 20 July 2004

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A detailed three‐dimensional refinement of the structure of hexagonal silver iodide from room‐temperature photographic data showed very little deviation from the ideal wurtzite‐type structure. Using anisotropic temperature factors a final R value of 6.6% was obtained. The space group is P63mc, a=4.592, c=7.510, c/a=1.635, μ=0.3747. A general linear relation of the position parameter μ to the c/a axial ratio was found to apply to compounds having this structure type.

Ultraviolet Absorption of Tetramethyl‐1,3‐Cyclobutanedione

Edward M. Kosower

J. Chem. Phys. 38, 2813 (1963); http://dx.doi.org/10.1063/1.1733607 (3 pages) | Cited 3 times

Online Publication Date: 20 July 2004

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The near‐ultraviolet spectrum of the cyclic 1,3‐dione, tetramethyl‐1,3‐cyclobutanedione, has maxima near both 3400 and 3000 Å. On the basis of absorption intensity (low), solvent shift (transition energy increases with Z), and position (with respect to cyclobutanone), the two transitions can be explained as n→π1*+π2* (lower transition energy) and n→π1*—π2* (higher transition energy). The assignment is similar to that used by Sidman and McClure for the 1,2‐dione, diacetyl. It is pointed out that s‐cis‐1,2‐diones should have low‐energy transitions at longer wavelengths than s‐trans‐1,2‐diones, and further, that a cyclic peroxy structure isomeric with the s‐cis‐1,2‐dione might possess sufficient stability for isolation. Evidence from early German literature is cited to show that 1,2‐benzoquinone does indeed exist in two isomeric forms; one, a red quinonoid form and a second, a colorless unstable form.

Infrared Spectrum and Vibrational Potential Function of Ketene and the Deuterated Ketenes

C. Bradley Moore and George C. Pimentel

J. Chem. Phys. 38, 2816 (1963); http://dx.doi.org/10.1063/1.1733608 (14 pages) | Cited 91 times

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Infrared spectra of solid ketene and ketene in argon reveal a new fundamental at lower frequency (CH2CO, 438 cm—1; CD2CO, 371 cm—1; CHDCO, 398 cm—1) than any previously reported. These spectra and additional gas‐phase spectra provide a basis for a reassignment of the vibrational spectrum. The vibrational potential function, centrifugal distortion constants, Coriolis coupling constants, and thermodynamic properties of ketene have been calculated. The out‐of‐plane hydrogen bending force constant is found to be surprisingly low, about one‐third of that for ethylene. In addition, the analysis of the rotational structure of several perpendicular bands yields improved estimates of the A moment of inertia and hence of the HCH angle (122.3°) and the C☒H bond length (1.079 Å) of ketene.

Acoustic Isotherms for Nitrogen, Argon, and Krypton

S. S. Lestz

J. Chem. Phys. 38, 2830 (1963); http://dx.doi.org/10.1063/1.1733609 (5 pages) | Cited 6 times

Online Publication Date: 20 July 2004

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Measurements of the sound velocity in nitrogen, argon, and krypton, and the derived heat capacities, are reported for a pressure range up to 12 atm and at two temperatures: the ice point and 303.7°K. It is believed that the data for nitrogen are more consistent than those reported by other investigators, while comparison data for argon and krypton are practically nonexistent.

Spin—Orbit Coupling and the Radiationless Processes in Nitrogen Heterocyclics

M. A. El‐Sayed

J. Chem. Phys. 38, 2834 (1963); http://dx.doi.org/10.1063/1.1733610 (5 pages) | Cited 259 times

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The matrix elements of the spin—orbit operator between the zero‐order (spin‐free) (n, π*) states of nitrogen heterocyclics are examined. It is found that generally, to the first order, there is no spin—orbit coupling between singlet and triplet states of the same configuration. The coupling between states of different configurations due to differences in the occupancy of the π* orbitals, but having the same nonbonding orbital, is found to have matrix elements similar to those resulting from the coupling between (π, π*) states, which McClure has shown to be unimportant. For the diazines (or polyazines), the coupling between different configurations due to a different occupancy of the nonbonding orbitals is found to have matrix elements which cancel one another. The general conclusion is thus reached that spin—orbit (s.o.) coupling between singlet and triplet (n, π*) states is unimportant to the first order. Using the observed polarization and lifetime data, it is estimated that the ratio
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has an upper value of 10—3. These results as well as vibrational overlap considerations suggest that the enhancement of the efficiency of the intersystem crossing in nitrogen heterocyclics with the lowest singlet state of the (n, π*) type might be due to an S(n, π*)→T(π, π*) rather than an S(n, π*)→T(n, π*) radiationless process. An alternative explanation to the one previously given for the observation of fluorescence of 9, 10‐diazaphenanthrene and s‐tetrazine is thus suggested. In these molecules, the strong interaction between the (n, π*) singlet levels might cause the lowest S(n, π*) excited level to have a lower energy value than the (π, π*) triplet level. This would therefore lead to a retardation of the intersystem crossing process and allow the fluorescence to be observed. The characteristics of the observed weak phosphorescence of 9,10‐diazaphenanthrene give spectroscopic support for this proposal.
For nitrogen heterocyclic molecules with the lowest singlet and lowest triplet states of the (π, π*) types, an examination of the quinoline total emission in comparison with that of the parent hydrocarbon, nath‐thalene, suggests an increase in the efficiency of the intersystem crossing process in quinoline. This is suggested to be due to the efficient S1(π, π*)→T2(n, π*)→T1(π, π*) radiationless process. A probable enhancement of the internal conversion processes in these molecules is suggested to be due to an increase in the density of states and the efficiency of the S(π, π*)↔S(n, π*) radiationless process due to a large vibrational overlap integral.

Orientation Birefringence of Macromolecular Solutions in Shear Flow and Electric Field

Shoichi Ikeda

J. Chem. Phys. 38, 2839 (1963); http://dx.doi.org/10.1063/1.1733611 (6 pages) | Cited 9 times

Online Publication Date: 20 July 2004

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The orientation distribution function of polar rigid macromolecules in dielectric media is obtained by solving the rotary diffusion equation in the steady state, when the solution flows with a constant velocity gradient and is acted upon by an electrostatic field perpendicular to the stream line. The optical properties, such as birefringence of the solution, are calculated by averaging the optical anisotropy of each macromolecule over all molecular orientations, which are weighted according to the orientation distribution function. The extinction angle and the amount of birefringence are expressed as functions of the velocity gradient and the electric field strength. The behavior of these properties is specifically dependent on the shape and the electric parameters of macromolecule. This method can provide new information about the macromolecular structure.

Infrared Vibrations of Crystalline Potassium Azide

James I. Bryant

J. Chem. Phys. 38, 2845 (1963); http://dx.doi.org/10.1063/1.1733612 (10 pages) | Cited 13 times

Online Publication Date: 20 July 2004

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The infrared spectrum of crystalline potassium azide has been investigated over the region from 4000 to 550 wavenumbers by using a grating spectrometer. Selection rules for internal and lattice vibrations and their combinations were calculated by using the ``unit‐cell'' method of Bhagavantam and Venkatarayudu. The spectrum was characterized by the splitting of fundamental absorptions and the occurrence of numerous lattice combinations symmetrically spaced about active and inactive fundamentals. From observed lattice combinations, tentative frequency assignments were made for the lattice modes. Polarized spectra indicate that most of these combinations are oriented in the xy plane of the crystal. The spectrum shows good agreement with the accepted crystal structure as described by the space group D4h18—I4/mcm.

Vibrational Fluorescence of Carbon Monoxide

Roger C. Millikan

J. Chem. Phys. 38, 2855 (1963); http://dx.doi.org/10.1063/1.1733613 (6 pages) | Cited 83 times

Online Publication Date: 20 July 2004

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Carbon monoxide gas (1 atm pressure) has been vibrationally excited by absorption of infrared light emitted by rich CH4☒O2 flames. The CO issued from a 286°K porous plate with a laminar flow velocity of 10 cm/sec. It was contained in an annular flow of argon of matched velocity. Resonance fluorescence was observed in the fundamental vibration—rotation band of CO at 2143 cm—1 when impurities were reduced below the ppm level. Intensity measurements showed that a vibrational temperature of 993°K had been reached by light absorption. Under the same conditions the rotational temperature remained at 286°K as shown by the intensity distribution of the rotational lines. Trapping of the resonance radiation permitted observation of the vibrational excitation for 0.2 sec after removal of the exciting light. The rate of the quenching reaction CO (v=1)+M→CO (v=0)+M has been determined from Stern—Volmer quenching curves for the collision partners H2, HD, D2, He, Ne, and O2. An extreme dependence of collisional vibrational relaxation time upon collision mass has been observed, as predicted by theory. Oxygen is anomalously efficient as a collision partner by several orders of magnitude.

Monte Carlo Procedure for Statistical Mechanical Calculations in a Grand Canonical Ensemble of Lattice Systems

Dwayne A. Chesnut and Zevi W. Salsburg

J. Chem. Phys. 38, 2861 (1963); http://dx.doi.org/10.1063/1.1733614 (15 pages) | Cited 33 times

Online Publication Date: 20 July 2004

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The Monte Carlo method of estimating statistical mechanical averages in the petite canonical ensemble, described by Rosenbluth et al., Wood and Parker (for fluid systems), and Salsburg et al. (for lattice models), has been extended to a general multicomponent lattice model in a restricted grand canonical ensemble. The procedure is applied to the two‐dimensional traingular lattice gas with periodic boundary conditions at a supercritical temperature (βϵ= —ln2), and numerical results are presented for the energy, specific heat, density, isothermal compressibility, thermal‐expansion coefficient, and grand partition function (pressure) at Δ=0.1, 0.0, —0.1, —0.2, —0.3, —0.4, —0.6, —0.8 (with B=100); at B=16, 25, 36, 49, 64, 100, 196 (with Δ=0.0); where Δ=βμ—3βϵ; where ϵ is the nearest‐neighbor interaction; β=(kT)—1, where μ is the chemical potential; and B is the number of sites. These are compared (where possible) with previous (Salsburg et al.) and additional petite‐ensemble Monte Carlo results. This comparison emphasizes the different B dependence of intensive properties in these two ensembles and is supplemented by an asymptotic analysis of this difference. Properties in both ensembles display the type of irregular B dependence predicted by Lebowitz and Percus for very small systems. For the larger lattices, properties in the petite ensemble show a stronger B dependence than in the grand ensemble, which is in quantitative agreement with the leading term in the asymptotic analysis. A comparison with the exact analytical results (B= ∞, Δ=0) indicates that the accuracy of the Monte Carlo procedure for the grand ensemble can be reliably estimated by a statistical analysis of partial averages over the Markov chain.

Averaged‐Boltzmann‐Factor Theories for Nonelectrolyte Solutions

Zevi W. Salsburg

J. Chem. Phys. 38, 2876 (1963); http://dx.doi.org/10.1063/1.1733615 (4 pages) | Cited 1 time

Online Publication Date: 20 July 2004

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The concept of the one‐, two‐, and three‐liquid approximations to the theory of nonelectrolyte solutions, introduced by Scott in terms of averaged pair potential functions, is extended by defining suitably averaged Boltzmann weighting factors which are composition dependent. These approximations are introduced and treated by means of a perturbation theory similar to that used by Nosonow to obtain a unified presentation of the averaged potential n‐liquid approximations.

Infrared Spectra of Methylgermane, Methyl‐d3‐Germane, and Methylgermane‐d3

James E. Griffiths

J. Chem. Phys. 38, 2879 (1963); http://dx.doi.org/10.1063/1.1733616 (13 pages) | Cited 14 times

Online Publication Date: 20 July 2004

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The infrared spectra of gaseous CH3GeH3, CD3GeH3, and CH3GeD3 were observed in the range 4000–400 cm—1. The 12 fundamental frequencies for each molecule are assigned to normal modes and the spectra are discussed in some detail. Teller—Redlich product‐rule ratios support the assignments. The height of the barrier hindering internal rotation was found from measurements on twelve combination bands involving the torsional modes to have an average value of 1270 cal/mole. The torsional force constant was estimated to be 0.31×10—12 erg/rad. The corresponding barrier height and torsional force constant for methylsilane were estimated to be 1715 cal/mole and 0.44×10—12 erg/rad, respectively, from published data.
Analyses of the rotational structures of ν7–10 and of ν12 and 2ν12 in the spectrum of CH3GeH3 and of ν7–10 and ν12 in the spectrum of CD3GeH3 afforded values for the band origins, certain rotational constants and ζ7–12 for both molecules.

Electron Spin Exchange in Aqueous Solutions of K2(SO3)2NO

M. T. Jones

J. Chem. Phys. 38, 2892 (1963); http://dx.doi.org/10.1063/1.1733617 (4 pages) | Cited 28 times

Online Publication Date: 20 July 2004

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The electron spin exchange frequency of potassium peroxylamine disulfonate as a function of concentration has been studied by electron spin resonance techniques. The exchange frequencies have been calculated from measurements of the linewidths and the line separations using the modified Bloch equations. The frequencies thus obtained are in agreement with each other. The functional dependence of exchange frequency upon concentration can be expressed as ω=bCm, where m is of the order of unity. The effect of molecular oxygen upon the spin exchange measurements is described. The resonance line shape has been found to deviate from Lorentzian at low concentrations.

Stark Energy Levels of Symmetric‐Top Molecules

Jon H. Shirley

J. Chem. Phys. 38, 2896 (1963); http://dx.doi.org/10.1063/1.1733618 (18 pages) | Cited 29 times

Online Publication Date: 20 July 2004

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Calculations have been performed to determine the Stark energy levels of rigid symmetric‐top molecules. The continued fraction expression for the eigenvalues of the energy matrix is presented and techniques of evaluation described. Tables of reduced energy levels as a function of electric field are given for all rotational states through J=4. Graphs of these values and the effective dipole moments are included.

Bonding Wavefunctions in the Xenon Fluorides

Richard Bersohn

J. Chem. Phys. 38, 2913 (1963); http://dx.doi.org/10.1063/1.1733619 (2 pages) | Cited 4 times

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A quadrupole coupling criterion is proposed to evaluate the bonding in the xenon fluorides. Localized valence bonds will give a much higher quadrupole coupling constant for Xe131 than the delocalized linear combinations of p functions used in the polyhalides.

Zero‐Field Electron Magnetic Resonance in Some Inorganic and Organic Radicals

Terry Cole, Toshimoto Kushida, and Hanan C. Heller

J. Chem. Phys. 38, 2915 (1963); http://dx.doi.org/10.1063/1.1733620 (10 pages) | Cited 16 times

Online Publication Date: 20 July 2004

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Zero‐field electron magnetic resonance (EMR) spectra have been observed for several dilute paramagnetic systems. Among these are peroxylamine disulfonate ions in aqueous solutions, Cr3+ in single crystals of MgO, free radicals in x‐irradiated powders of malonic acid, potassium hydrogen malonate, dipotassium malonate, succinic acid, and glutaconic acid. Zero‐field spectra were observed by means of a marginal oscillator—detector similar to that of Benedek and Kushida. The zero‐field splittings in the systems studied were due exclusively to the hyperfine couplings between electronic and nuclear spins. Results obtained were in good agreement with high‐field EMR measurements on these systems. In several cases the hyperfine couplings were obtained with greater precision than at high field. In addition, the radical —OOC☒ĊH☒COO— was identified, for the first time, in irradiated dipotassium malonate by means of its zero‐field spectrum. No zero‐field lines could be detected in electron‐irradiated polyethylene. Advantages and disadvantages of the zero‐field technique are discussed.

Photolysis of Mixtures of Diethyl Ketone and Carbon Tetrachloride

Jessie E. Gregory and M. H. J. Wijnen

J. Chem. Phys. 38, 2925 (1963); http://dx.doi.org/10.1063/1.1733621 (6 pages) | Cited 4 times

Online Publication Date: 20 July 2004

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The photolysis of mixtures of diethyl ketone and carbon tetrachloride has been investigated at room temperature. The following reaction products were observed: CO, C2H6, C2H4, C4H10, CHCl3, C2H5CCl3, C2Cl6, C2H5 (CH3) CHCOC2H5, and CH3 (CCl3) CHCOC2H5. Primary radicals produced by photolysis of diethyl ketone and carbon tetrachloride are C2H5, CCl3, and Cl. Chlorine atoms react with diethyl ketone to form HCl and CH3CHCOC2H5 radicals. Disproportionation and recombination reactions involving CCl3, C2H5, and CH3CHCOC2H5 radicals are largely influential in the formation of many of the products. The ratios of disproportionation over recombination for CCl3 and C2H5 radicals and for CCl3 and CH3CHCOC2H5 radicals were obtained together with various ratios of other rate constants.

Formation of Fragment Ions from CH3Te125 and C2H5Te125 Following the Nuclear Decays of CH3I125 and C2H5I125

Thomas A. Carlson and R. Milford White

J. Chem. Phys. 38, 2930 (1963); http://dx.doi.org/10.1063/1.1733622 (5 pages) | Cited 24 times

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The relative abundances of the fragment ions that result respectively from the nuclear decays of CH3I125 and C2H5I125 (I125 undergoes electron capture to give Te125) have been measured with a specially designed mass spectrometer. The data from both studies are similar and give evidence as follows of the highly destructive nature of the decay: (1) Only about 1% of the Te—hydrocarbon ions appear to remain intact in spite of the fact that these ions would be expected to be collected with high efficiency; (2) In both studies a large number of tellurium ions is found with charges as high as 18 and with an average charge of about 9; (3) Finally, in both studies, the singly, doubly, and triply charged carbon ions are found in greater abundance than the hydrocarbon ions. The cause of this extensive ionization and fragmentation is ascribed primarily to a series of Auger processes that occur subsequently to the formation of inner orbital vacancies in Te125 as the result of electron capture and internal conversion in the decay of I125.

Photolysis of Nitrogen Dioxide at 3660 and 4047 Å at 25°C

H. W. Ford and S. Jaffe

J. Chem. Phys. 38, 2935 (1963); http://dx.doi.org/10.1063/1.1733623 (8 pages) | Cited 16 times

Online Publication Date: 20 July 2004

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Nitrogen dioxide was irradiated at 3660 and 4047 Å at various pressures of NO2, with and without CO2, NO, and N2 as added gases. The data indicate a primary dissociation at 3660 Å and shorter wavelengths corresponding to energies greater than the ON☒O bond energy. At 4047 Å, the data are explained by an excited‐molecule mechanism. Isotopic oxygen scrambling experiments at 4047 Å indicate the probability of reactions to produce oxygen atoms at that wavelength, but photolysis of NO2 at trace concentrations and high inert‐gas pressures indicates that these atoms are not derived from the unimolecular decomposition of the photoactivated molecule. The inhibition of the quantum yield by NO addition was pressure‐dependent, lending further support to the premise that oxygen atoms are important in the mechanism at 4047 Å. It is postulated that the reaction NO2*+NO2→N2O3+O is the source of atomic oxygen.

Surface Studies by Spectral Analysis of Internally Reflected Infrared Radiation: Hydrogen on Silicon

G. E. Becker and G. W. Gobeli

J. Chem. Phys. 38, 2942 (1963); http://dx.doi.org/10.1063/1.1733624 (4 pages) | Cited 45 times

Online Publication Date: 20 July 2004

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An investigation of the adsorption of hydrogen on a large single crystal of silicon has been made by infrared methods in an ultrahigh vacuum system. A broad absorption line at 4.85 μ has been ascribed to a monolayer of atomic hydrogen chemisorbed on clean silicon. The increase in intensity and changes in position and shape of this line produced by hydrogen ion bombardment are reported. The primary purpose of this work was to evaluate the technique of spectral analysis of infrared radiation multiply internally reflected in a semiconductor as a general tool for the study of adsorption on clean semiconductor surfaces. It is concluded that the method can indeed be useful in favorable cases, although formidable experimental difficulties stand in the way of a very general application.

Theory of Dissociation Pressures of Some Gas Hydrates

V. McKoy and O. Sinanoğlu

J. Chem. Phys. 38, 2946 (1963); http://dx.doi.org/10.1063/1.1733625 (11 pages) | Cited 73 times

Online Publication Date: 20 July 2004

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Dissociation pressures of some gas hydrates have been evaluated using the Lennard‐Jones 12–6, 28–7, and Kihara potentials in the Lennard‐Jones‐Devonshire cell model. The Lennard‐Jones 28–7 potential gives the least satisfactory results. The Lennard‐Jones 12–6 potential works satisfactorily for the monatomic gases and CH4 but poorly for the rodlike molecules C2H6, CO2, N2, O2, C2H4. This failure may be due to (i) distortions of the hydrate lattice, (ii) neglect of molecular shape and size in determining the cavity potential (iii) barrier to internal rotation of the molecule in its cavity. A crude model for the lattice shows that it is not distorted. The Kihara potential predicts better dissociation pressures for the hydrates of the rodlike molecules. Unlike the previously used Lennard‐Jones 12–6 potential, it depends on the size and shape of the interacting molecules. The absence of lattice distortions, improved dissociation pressures through the use of the Kihara potential and the restriction of the motion of the solute molecule to around the center of a cavity makes a large barrier to rotation unlikely. A small barrier may still be present.

Excluded‐Volume Effect for Two‐ and Three‐Dimensional Lattice Models

C. Domb

J. Chem. Phys. 38, 2957 (1963); http://dx.doi.org/10.1063/1.1733626 (7 pages) | Cited 109 times

Online Publication Date: 20 July 2004

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An analysis is undertaken of mean‐square sizes of self‐avoiding walks enumerated exactly on various two‐ and three‐dimensional lattices. It is suggested that for all three‐dimensional lattices the mean‐square size tends to an asymptotic relation 〈rn2〉≃A1n6/5+A2, while for two‐dimensional lattices the corresponding relation is 〈rn2〉≃B1n3/2+B2n. The constants A1, B1 decrease as the coordination of the lattice increases. Estimates of A1, A2 are given for the fcc, bcc, simple cubic, and diamond lattices, and of B1, B2 for the triangular and simple quadratic lattices.

Microwave Spectrum, Structure, and Quadrupole Coupling Constant Tensor of Ethyl Bromide

Cyprian Flanagan and Louis Pierce

J. Chem. Phys. 38, 2963 (1963); http://dx.doi.org/10.1063/1.1733627 (7 pages) | Cited 32 times

Online Publication Date: 20 July 2004

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The microwave spectra of 10 isotopic species of ethyl bromide have been measured and assigned, viz., the 79Br and 81Br species of CH3CH2Br, CH3CD2Br, CD3CH2Br, CH313CH2Br, and 13CH3CH2Br. The spectra reported lie in the region of 18 to 31 kMc. The complete structure has been determined by the substitution method, giving the following bond parameters: CC = 1.518 Å, CBr = 1.950 Å, CCBr = 111°2′, CH (methylene) = 1.087 Å, HCH (methylene) = 109°54′, CCH (methylene) = 112°15′, HCBr = 105°25′, CH (methyl) = 1.093 Å, and HCH (methyl) = 108°52′. The principal quadrupole coupling parameters have been determined to be χzz = 541 Mc, χxx = —267 Mc, and χyy = —274 Mc for C2H579Br and χzz = 450 Mc, χxx = —220 Mc, and χyy = —230 Mc for C2H581Br. Through the analysis of second‐order effects of quadrupole coupling on hyperfine structure, it was determined that, within experimental error, the CBr internuclear line and the ``z'' principal quadrupole axis coincide, indicating that the CBr bond is not bent. The barrier to internal rotation, recalculated using Lide's splitting measurements, and the above structure is 3684 cal/mole.

Spin—Lattice Relaxation due to Translational Diffusion in LiBr

R. R. Allen and M. J. Weber

J. Chem. Phys. 38, 2970 (1963); http://dx.doi.org/10.1063/1.1733628 (5 pages) | Cited 3 times

Online Publication Date: 20 July 2004

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Nuclear spin—lattice relaxation in LiBr due to translational diffusion of Li ion vacancies has been established from an investigation of the temperature dependence of the relaxation time T1. The Li and Br T1's exhibit minima at different temperatures, and are found to arise from magnetic dipole—dipole and quadrupolar interactions, respectively. Since both relaxation mechanisms are observed in the same crystal environment, the results have been used to compare and correlate the relaxation theories of Torrey and Reif and their extensions to LiBr. The magnitude and temperature dependence of the relaxation are in agreement with theoretical predictions. The effects of vacancies caused by (1) the presence of divalent impurity ions, and (2) intrinsic thermal generation are observed and the activation energies for their formation and diffusion are determined. Additional measurements of line narrowing and ionic conductivity are reported which confirm the properties of the diffusive motion.
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