Index of content:
Volume 36, Issue 4, 15 February 1962
36(1962); http://dx.doi.org/10.1063/1.1732680View Description Hide Description
The results of luminescence studies of thulium trisbenzoylacetonate and thulium trisdibenzoylmethide are reported. Selective excitation of the 1 G 4 level of Tm3+ via energy transfer has been achieved. Emission from the 3 F 4 level of the ion has been observed, and all the groups of lines appearing in the visible and near infrared spectral regions have been assigned. A quenching mechanism involving vibrational coupling of the ion with the ligand is discussed. Ligand field splitting is reported.
Heat Capacities and Thermodynamic Functions of YH2 and YD2 from 5° to 350°K and the Hydrogen Vibration Frequencies36(1962); http://dx.doi.org/10.1063/1.1732681View Description Hide Description
The heat capacities of pure YH2 and YD2 were measured by an adiabatic method from 5° to 350°K. The compounds were found by x‐ray analyses to consist of a single phase, with the yttrium atoms in face‐centered cubic positions. Below 16°K the heat capacities of the two compounds are equal within experimental error, between 16° and 90°K the heat capacity of the hydride is about 0.02 cal deg—1 mole—1 greater than that of the deuteride, and at higher temperatures that of the deuteride becomes appreciably greater. The difference in the heat capacities above 100°K is ascribed to a single optical vibration of the hydrogen atoms, whose frequency is shifted upon isotopic substitution. The difference in the heat capacities of YH2 and YD2 in the temperature range 100° to 350°K is fitted to ±0.02 cal deg—1 mole—1 with Einstein heat capacity functions and a frequency of 1030±30 cm—1 for YH2 and 1030/√2 for YD2. These results are compared with those obtained by inelastic neutron scattering experiments.
The values obtained for the heat capacity,entropy,enthalpy and Gibbs free‐energy function for YH2 at 298.15°K are 8.243±0.016 cal deg—1 mole—1, 9.175±0.018 cal deg—1 mole—1, 1403±3 cal mole—1 and —4.470±0.009 cal deg—1 mole—1, respectively. The corresponding values for YD2 are 10.773±0.022, 10.294±0.021, 1659±3 and —4.729±0.010. The enthalpy of formation of YH2 minus the enthalpy of formation of YD2 is calculated to be 0.78±0.08 kcal mole—1 at 0°K and 0.55±0.08 kcal mole—1 at 298.15°K.
Chain Model for Polyelectrolytes. VII. Potentiometric Titration and Ion Binding in Solutions of Linear Polyelectrolytes36(1962); http://dx.doi.org/10.1063/1.1732682View Description Hide Description
The electrostatic potential about a rodlike polyion in an aqueous solution containing added simple electrolyte is calculated by numerical integration of the Poisson‐Boltzmann equation. The results are applied to the calculation of the ionic distributions about the polyion and the potentiometric titration curves of polyweak acids. The nature of ion binding is discussed in terms of a molecular model and it is found that the degree of ion binding f * may be expressed aswhere the parameters are defined in the text.
36(1962); http://dx.doi.org/10.1063/1.1732683View Description Hide Description
At 4358 A at room temperature the quantum yield for the primary dissociation of biacetyl increases with intensity. It is thus implied that the primary process is second order in some active species. By use of the rotating sector it is shown that the species responsible for this effect has a mean life close to that ascribed to an excited triplet state for biacetyl. At higher temperatures this intensity effect disappears and one of the products strongly inhibits both the phosphorescence and the primary dissociation. At these temperatures the data may best be treated by assuming that the triplet state of biacetyl undergoes a unimolecular dissociation with an activation energy of about 15 kcal.
36(1962); http://dx.doi.org/10.1063/1.1732684View Description Hide Description
The nucleation kinetics of zinc crystals from the vapor onto Pyrex glass have been measured over a range of more than 106 in zincvapor pressure. Results can be brought into accord with classical nucleation theory only by the assumption of a thermal accommodation coefficient of less than unity for the self‐adsorbed zinc layer on the glass substrate.
36(1962); http://dx.doi.org/10.1063/1.1732685View Description Hide Description
The fluorescent intensity of solutions of diphenyloxazole (PPO) in cyclohexane is measured as a function of concentration for excitation by γ rays. The fluorescencespectrum of the solutions when excited by uv is also recorded. These uv measurements, together with the results of β excitation, were used to examine the quenching influence of oxygen on the solute fluorescence and on the energy transfer from cyclohexane. The decay times of the solutions are measured. The results are interpreted to show: (1) a tendency of PPO to form molecular complexes in cyclohexane and (2) a ``static'' character for the oxygen quenching of cyclohexane. The dependence of transfer probability on solute concentration is discussed.
36(1962); http://dx.doi.org/10.1063/1.1732686View Description Hide Description
An investigation of the pyrolysis of di‐tertiary butyl peroxide over the range 27–130 mm Hg pressure and 130–160°C has shown that the experimental stoichiometry is 3.0 rather than the previously reported 2.9. Trace amounts of t‐BuOH (0.5 to 1.0%), isobutylene oxide (1–2%) and t‐BuOMe (0.02%) have been identified as well as biacetonyl and small amounts of other ketones. By using spherical vessels and octopus vessels of large surface/volume ratio, it is shown that the previously reported scatter in the Arrhenius parameters can be attributed to temperature gradients established in the vessel. This is confirmed by direct measurement of the gas temperature with fine thermocouple wires in thin glass wells.
The best rate constant for the first‐order decomposition in the absence of temperature gradients is given by: logk=15.6–37 400/4.575T sec—1 with an uncertainty in E of about ±0.5 kcal. Assuming zero activation energy for the recombination of t‐butoxy radicals, this gives the peroxide bond dissociation energy of 37.4±0.5 kcal/mole. An estimate of the standard entropy change for dtBP→2 t‐BuO gives the remarkably low value of 108.2 l/mole‐sec for the Arrhenius factor for the recombination of t‐BuO radicals. It is shown that such a low value is needed to explain the concordance in Arrhenius parameters for liquid and gas state pyrolyses.
The isobutylene oxide puts a limit to the chain contribution of about 1 to 2%. The t‐BuOH and t‐BuOMe yields permit independent estimates of the rate of dissociation of t‐BuO radicals in fair agreement with each other and other investigations.
The explosion limits for the decomposition are estimated to be about 7.5 atm (150°C). The present work confirms the importance of temperature gradients in contributing to spurious activation energies for very exothermic reactions.
Infrared Spectra in Polarized Light and Vibrational Assignment of the Infrared Active Modes of Anthracene and Anthracene‐d 1036(1962); http://dx.doi.org/10.1063/1.1732688View Description Hide Description
Infrared spectra of anthracene and anthracene‐d 10 of high deuterium content are reported. The spectra were measured in the gas phase, in solution, in KBr pellets, and in single crystals with polarized radiation. The experimental dichroism of the observed bands has been used to furnish a vibrational assignment of the infrared active modes. This assignment shows striking similarities with the assignment given in the literature for naphthalene.
36(1962); http://dx.doi.org/10.1063/1.1732689View Description Hide Description
A kinetic analysis is made of the thermal diffusion of a dilute impurity in an fcc metal. Expressions are derived for the impurity current, the steady‐state Soret gradient, and the mean‐atom displacement. It is shown how the ``heats of transport'' appearing in these expressions can be studied experimentally. An extension of the analysis to cases of nonthermal type gradients, in particular a chemical concentration gradient, is briefly considered.
36(1962); http://dx.doi.org/10.1063/1.1732690View Description Hide Description
Values of the second virial coefficient for the three‐parameter spherical shell potential are tabulated over wide ranges of temperature and shell size. The potential, which is not new, results from the interaction of two spherical surfaces having uniform distributions of Lennard‐Jones (6–12) sites.
An objective comparison is made between the tabulated values and the literature values for second virial coefficients, from which the potential parameters for twenty compounds are determined. Generally, the spherical shell potential generates a better fit than does the parent Lennard‐Jones potential. The potential parameters found are in good agreement with expectations based upon density and interatomic distance data.
36(1962); http://dx.doi.org/10.1063/1.1732691View Description Hide Description
A pure nitrogen afterglow has been studied spectroscopically at pressures up to 1 atm and up to several seconds after the discharge. The first positive bands of nitrogen continue to show an unchanged preferential enhancement of bands with v′=11 at high pressure, but their decay with time, measured photoelectrically, indicates that at high pressure N(4 S) atoms must be removed by a more rapid process than recombination in triple collisions; it is suggested that this may be a two‐body reaction with an oxide of nitrogen. Forbidden radiation from O, N, and N2 predominates over the first positive bands at high pressure, and a high degree of immunity toward deactivating collisions is shown to be required for the metastable states N(2 P), O(1 S), and N2(A 3Σ u +). The absolute intensity and decay of the forbidden radiation indicates that O(1 S) must be created in the afterglow while N(2 P), and to some extent N2(A 3Σ u +), survive from the discharge. The observations favor a long radiative lifetime near 1 sec for N2(A 3Σ u +).
36(1962); http://dx.doi.org/10.1063/1.1732692View Description Hide Description
Previous discussions of hypervirial theorems in wave mechanics have been extended in three ways. (1) A particular class of operators called compound hypervirial operators is introduced, and the particular point transformations which they may be said to generate are studied. (2) An example of these new operators is an electron‐correlation hypervirial, which modifies a wave function when two electrons are near together but exerts little influence when they are a long way apart. (3) A study is made of possible wave functions for a diatomic molecule which satisfy the Hellmann‐Feynman theorem and provide a means of deducing the shape of the potential energy curve, or its slope at a particular internuclear distance.
36(1962); http://dx.doi.org/10.1063/1.1732693View Description Hide Description
An atom will dissociate from a compound if the atom receives a recoil momentum greater than some average value Q 0. Considering a polyatomic molecule as composed of point‐mass atoms, there is derived an equation which relates Q 0 to the bondenergy,bond angles and distances, and masses of the atoms in the molecule. The minimum net recoil energy required for bond rupture, the kinetic energy of the recoiling radicals, and the internal energy of the radical originally bonded to the activated atom are calculated for a series of simple alkyl halides.
36(1962); http://dx.doi.org/10.1063/1.1732694View Description Hide Description
Following the absorption of a thermal neutron by 127I or 79Br, the neutron‐binding energy is frequently released in the form of a gamma‐ray cascade. As a result of partial cancellation of gamma‐ray momenta, a small fraction of the activated halogens will not receive sufficient recoil momentum to rupture from their parent compound. The gas‐phase failures to bond rupture following 127I(n, γ) 128I, and 79Br(n, γ) 80Br activation were found experimentally to be: CH3I—1.09, CD3I—0.68, CF3I—0.12, CH2I2—0.068, C2H5I—0.082, n‐C3H7I—0.66, i‐C3H7I—0.30, CH3Br—0.25, CD3Br—0.20, CH2Br2—0.12, CF3Br—0.11, CF2Br2—0.093, CHClBr2—0.087, CCl3Br—0.066, CHBr3—0.05, CBr4—0.03, C2H5Br—0.33, and 1,1‐C2H4Br2—0.17%. These data are correlated with the calculated recoil energies required for bond rupture (preceding article). Using as a basis the distribution of net gamma‐ray energies calculated by the random‐walk method for the 35Cl(n, γ) 36Cl process, the kinetic‐energy distributions of the dissociated 128I or 80Br are approximated. These data suggest that the extent of hot‐atom reaction of 128I or 80Br with CH4 should not depend upon the parent molecule from which the activated halogen dissociates.
36(1962); http://dx.doi.org/10.1063/1.1732695View Description Hide Description
Absorption coefficients of sulfur dioxide in the spectral region 1050–2170 A were measured photoelectrically at about 500 points of the spectrum. The absorptionspectrum below 1350 A is interpreted in terms of a Rydberg series converging upon the ionization potential of 12.34 ev obtained by the photoionization method.
36(1962); http://dx.doi.org/10.1063/1.1732696View Description Hide Description
For LiD and DF, the deuteron quadrupole coupling constant (eqQ/h) has been calculated with single‐determinant SCF‐LCAO‐MO functions. The results obtained are 38 kc/sec for LiD and 373 kc/sec for DF, in rather satisfactory agreement with the recently measured values (30±3 kc/sec for LiD and 340±40 kc/sec for DF). To evaluate the molecular integrals required for the determination of q, a formulation in terms of confocal elliptic coordinates was used. This made possible the introduction of certain auxiliary functions that are very convenient for the calculation of field gradient and related integrals. A comparison of the quadrupole coupling constants obtained with a number of different molecular orbital functions is presented. The results demonstrate the importance of using atomic basis functions with exponents optimized for the molecular system and suggest that exact Hartree‐Fock functions may yield relatively reliable values for field gradients and other one‐electron weak‐interaction parameters.
A calculation of the field gradient at the Li nucleus (q = —0.0401 a.u.) yields a value of —3.7×10—26 cm2 for the Li7quadrupole moment when combined with the coupling constant measurement of +346±1 kc/sec.
36(1962); http://dx.doi.org/10.1063/1.1732697View Description Hide Description
The microwave spectra of eight isotopic species of tertiary butyl acetylene and four isotopic species of tertiary butyl cyanide have been measured and analysed. Some transitions in excited vibrational states have been assigned. Measurements of the Stark effect lead to a dipole moment of 0.661±0.004 D for (CH3)3CCCH and 3.95±0.05 D for (CH3)3CCN. From the isotope shifts in the moments of inertia the following bond distances (rs ) are obtained: r(C≡C) = 1.209±0.001 A and r(≡C–H) = 1.056±0.001 A in (CH3)3CCCH; r(C≡N) = 1.159±0.001 A in (CH3)3CCN. The tertiary butyl group appears to have very nearly the same dimensions in these two compounds as in (CH3)3CH and (CH3)3CF. The tertiary carbon atom cannot be located with high precision, but the best estimates lead to a C–C≡ distance of 1.495±0.015 A in both (CH3)3CCCH and (CH3)3CCN. This is 0.02–0.04 A longer than the normal value for this distance. There appears to be a consistent tendency for the (CH3)3C— group to lengthen the adjacent bond, but it is difficult to find an explanation in terms of existing theories.
Heat Capacity and Entropy of CoCl2 and MnCl2 from 11° to 300°K. Thermal Anomaly Associated with Antiferromagnetic Ordering in CoCl236(1962); http://dx.doi.org/10.1063/1.1732698View Description Hide Description
The heat capacities of MnCl2 and CoCl2 have been measured between 11° and 300°K. By the use of the measurements of Murray on MnCl2 at lower temperatures the lattice and magnetic contributions to the heat capacity and entropy of MnCl2 have been evaluated. CoCl2 has a lambda peak in heat capacity at 24.71±0.05°K associated with the cooperative ordering of the magnetic moments of the cobaltous ions. The entropy change associated with this cooperative ordering is R ln2. Smooth values of the heat capacity,entropy,enthalpy, and free energy are tabulated at selected temperatures. The values of the entropy and enthalpy at 298.15°K are: MnCl2, S° = 28.26±0.05 cal deg—1 mole—1, H°–H 0° = 3602±8 cal mole—1; CoCl2, S° = 26.09±0.05 cal deg—1 mole—1, H°–H 0° = 3375±8 cal mole—1.
Heat Capacity and Entropy of CuCl2 and CrCl2 from 11° to 300°K. Magnetic Ordering in Linear Chain Crystals36(1962); http://dx.doi.org/10.1063/1.1732699View Description Hide Description
The heat capacities of CuCl2 and CrCl2 have been measured between 11° and 300°K. The contributions to the entropy and heat capacity arising from the ordering of the magnetic moments are evaluated. Maxima in the heat capacity are found at 23.91±0.1°K for CuCl2 and 16.06±0.05°K for CrCl2. Both compounds show gradual maxima in the magnetic contribution to the heat capacity at higher temperatures. These are interpreted as short‐range one‐dimensional ordering arising from relatively strong antiferromagnetic coupling within the chains of atoms which make up these crystals. At lower temperatures relatively weak interactions between atoms in different chains cause the development of long‐range order. By use of the Ising model to describe interactions within a chain and a molecular field to describe the secondary interactions, an approximate theoretical treatment is given. Smooth values of the heat capacity,entropy,enthalpy, and free energy are tabulated at selected temperatures. The values of the entropy and enthalpy at 298.15°K are: CuCl2, S° = 25.83±0.05 cal deg—1 mole—1, H°–H 0° = 3581±7 cal mole—1; CrCl2, S° = 27.56±0.05 cal deg—1 mole—1, H°–H 0° = 3593±7 cal mole—1. By use of equilibrium data of Doerner and of Sano the standard heat of formation of CrCl2 is calculated to be —94.52±0.4 kcal.