Index of content:
Volume 40, Issue 2, 15 January 1964
40(1964); http://dx.doi.org/10.1063/1.1725106View Description Hide Description
Some recent data on the shock‐wave compression of sodium chloride are used to obtain the equation of state and the volume dependence of some thermodynamical functions in the pressure range from 50 to 800 kilobars. Various possible expressions for the free energy are assumed and the results are discussed and compared between themselves and with the available experimental data. It is found that the data are not sufficient to make a decision in favor of any of the assumptions, because in all the cases the agreement with the available data is very good.
Hyperfine Structure in the Microwave Spectrum of HDO, HDS, CH2O, and CHDO : Beam‐Maser Spectroscopy on Asymmetric‐Top Molecules40(1964); http://dx.doi.org/10.1063/1.1725107View Description Hide Description
Hyperfine structure in the 220→221 rotational transition of HDO at 10 278.2 Mc/sec and HDS at 11 283.8 Mc/sec, and in the 211→212 rotational transition of CH2O at 14 488.6 Mc/sec and CHDO at 16 038.1 Mc/sec, has been investigated with a high‐resolution beammasermicrowave spectrometer.Linewidths of 5 kc/sec have been obtained. The hyperfine Hamiltonian for an arbitrary number of nuclei with quadrupole, spin—rotation, and spin—spin interactions is discussed, and the matrix elements of the Hamiltonian and the intensities of hyperfine transitions calculated in terms of the tabulated 6j coefficients. Quadrupole and spin—rotation constants and bond lengths which have been determined are, for the 220 state of HDO: (eqJQ)D = 79.3±0.3 kc/sec, C H = —43.47±0.11 kc/sec, C D = —2.33±0.02 kc/sec; for the 221 state of HDO: (eqJQ)D = 79.6±0.3 kc/sec, C H = —43.63±0.13 kc/sec, C D = —2.20±0.02 kc/sec; for the 220 state of HDS: (eqJQ)D = 42.9±0.4 kc/sec, C H = —25.03±0.13 kc/sec, C D = —0.47±0.02 kc/sec; for the 221 state of HDS: (eqJQ)D = 43.3±0.4 kc/sec, C H = —25.45±0.13 kc/sec, C D = —0.22±0.02 kc/sec; for CH2O: C H (211) — C H (212) = 2.26±0.13 kc/sec, C H (211) = 0.65±0.50 kc/sec, 〈1/r HH 3〉—⅓ = 1.898±0.017 Å; for CHDO: (eV ξξ Q)D = 170.0±2.0 kc/sec (where V ξξ is the second derivative of the electrostatic potential along the CD bond), C H (211) — C H (212) = 2.42±0.50 kc/sec, C D (211) — C D (212) = 0.25±0.10 kc/sec, C H (211) = 0.2±1.0 kc/sec, C D (211) = 0.13±0.20 kc/sec, and 〈1/r HD 3〉—⅓ = 1.88±0.10 Å. The V ξξ calculated from the deuteron quadrupole coupling constants are, for HDO: 1.56×1015 statvolt/cm2; for HDS: 0.76×1015 statvolt/cm2; and for CHDO: 0.83×1015 statvolt/cm2.
40(1964); http://dx.doi.org/10.1063/1.1725108View Description Hide Description
The spectra of chromium acetylacetonate and several derivatives have been recorded at 77° and 4°K. The structure in the 12 000–15 000 cm—1 region has been assigned to vibronic components of 2 E←4 A 2 and the 2 T 1 state located. The effect of ligand halogenation on the trigonal field splitting is small.
40(1964); http://dx.doi.org/10.1063/1.1725109View Description Hide Description
The BF3 complexes of ethyl ether, ethyl sulfide, and triethylamine were studied. Isotopic equilibrium constants for the reactions were measured at several temperatures for each of the three systems. Vapor pressures of the ethyl sulfide complex, and rates of exchange of boron between BF3 and BF3·Et3N were also determined.
40(1964); http://dx.doi.org/10.1063/1.1725110View Description Hide Description
For the case of nonadiabatic, steady‐state crystallization in a supercooled liquid, the class of possible interface shapes, consistent with the interface kinetic restrictions, is examined. For transformations obeying isotropic kinetics, the allowed class of crystal—liquid interfaces consists of denumerable combinations of dendrites and cells. For transformations obeying nonisotropic kinetics, certain classes of kinetic laws preclude the satisfaction of a steady‐state process. However, other classes of nonisotropic kinetic laws permit a steady‐state process. For the latter case, the allowed steady‐state interface shapes are of the same class as those permitted for the case of isotropic kinetics.
40(1964); http://dx.doi.org/10.1063/1.1725111View Description Hide Description
Free evaporation of rhombic sulfur is shown to give rise solely to S8 vapor molecules, whereas the sublimation of an allotropic form (Engel's sulfur) produces only S6 vapor molecules. The vapor composition characteristic of equilibrium can be produced by mixing any allotropic form of sulfur with commercial Al2O3, which evidently catalyzes the transformation among sulfur species. The evaporation coefficients of S6 and S7 molecules from a rhombic sulfur surface have been measured. The behavior of other allotropes (Sμ, Sπ) is described as observed by mass spectrometry.Mass spectra of S6 and S8 molecules have been determined directly as a function of temperature and that of S7 deduced from a vapor mixture of S6, S7, and S8. Ionization efficiency curves and appearance potentials of the major ionic species are reported. Paramagnetic resonance measurements have been used to help elucidate the mechanism of catalysis.
40(1964); http://dx.doi.org/10.1063/1.1725112View Description Hide Description
A cryostat is described in which magnetic susceptibility measurements may be made by an audio‐frequency mutual induction technique at temperatures down to 0.35°K. Below 2°K the specimens are in direct contact with liquid He3. Results of measurements on several compounds are presented. The powdersusceptibility of has been found to obey a Curie—Weiss law. Both powdered Co(CH3COO)2·4H2O and powdered Ni(CH3COO)2·4H2O are observed to be paramagnetic to the lowest temperatures attained; the former salt does not exhibit the anomaly at 0.6°K found in earlier studies employing a magnetic cooling technique. The powdersusceptibility of Mn(HCOO)2·2H2O suggests the existence of significant coupling among many of the Mn++ moments, but no evidence was found of a cooperative transition above 0.56°K.
40(1964); http://dx.doi.org/10.1063/1.1725113View Description Hide Description
The kinetic data of Rollefson and Faull for the iodine‐catalyzed decomposition of acetaldehyde are summarized, and the RF mechanism of the reaction is critically reviewed. A new mechanism for the iodine‐catalysis reaction is presented. Properties predicted from the new mechanism are compared with the observed reaction rates, reaction orders, and the unusual experimental behavior of the reactive system. Excellent agreement is found. The reaction is initiated by an iodine atom attack on acetaldehyde to abstract a hydrogen atom and produce hydrogen iodide and an acetyl radical. The rate‐determining step for the reaction is the decomposition of the acetyl radical, which is a unimolecular pressure‐dependent decomposition. The characteristic falloff of the rate of decomposition in the later stages of reaction is shown to be the result of this pressure dependence. The mechanism is also applied to the iodine‐catalyzed decomposition of propionaldehyde. Satisfactory agreement with observed reaction orders and reaction rates is obtained. From these data the decomposition kinetics of the propionyl radical is predicted to be pressure‐dependent at normal experimental pressures.
40(1964); http://dx.doi.org/10.1063/1.1725114View Description Hide Description
Absolute infrared intensities have been measured for ν2 and ν3 of CS2 in the solid phase. Path lengths were measured by counting interference fringes as the solid is condensed onto a cold window. The index of refraction of the solid film is estimated from the intensity of the fringe pattern on different windows of known index of refraction. The problem of choosing a suitable background is discussed. Although two different kinds of films were formed, the intensities were identical within experimental error. The intensities found for ν2 and ν3 were 850±100 and 80 000±14 000 darks, respectively. These values are quite comparable to the intensities found in liquid CS2, and are both higher than found in the gas phase. Hence, the intensity sum rule does not hold for this crystal. The observed intensification is compared with that predicted from the simple field effect, using an elliptical cavity, and found to agree quite well. Hence, we conclude that CS2 molecules do not interact strongly in the crystal in ways which affect the intensity. The ``ideal'' behavior is tested further in a comparison of the observed frequency shift with that calculated from the Kirkwood—Bauer—Magat theory; again the agreement is quite good for ν3 where the predicted shift is large. For ν2, with a smaller predicted shift, the agreement is poor, indicating that other forces are at least as large.
Finally, the infrared spectra and x‐ray powder pattern are used in combination to estimate the crystal structure. Both are consistent with an orthorhombic space group D 2h 12, with two molecules per unit cell (a=5.45, b=8.16, and c=3.74 Å). Although this space group is not determined uniquely, the crystal splitting was calculated from the dipole—dipole model, assuming that the structure was approximately correct in locating the molecules. The calculated splitting for ν3, where it is large, agrees very well with the observed splitting; for ν2, where the calculated dipole—dipole splitting is small, the agreement with experiment is poor.
40(1964); http://dx.doi.org/10.1063/1.1725115View Description Hide Description
Infrared spectra of gaseous digermane and of digermane‐d 6 were recorded under medium resolution from 4000–250 cm—1 and the Raman displacements were obtained photoelectrically from 100–2600 cm—1 for the liquid state. The 12 fundamental frequencies for each molecule were assigned to the normal modes and digermane was shown to have the D 3d ethanelike structure.
The rotational structures of the eu fundamentals of Ge2H6 and the ν8 fundamental of Ge2D6 were resolved and analyzed. Results from the zeta sum rule confirmed the hindered rotator structure and four combination bands were used to estimate the barrier hindering internal rotation as 1490±200 cal/mole.
40(1964); http://dx.doi.org/10.1063/1.1725117View Description Hide Description
The gaseous infrared spectra of CH2N2, CHDN2, CD2N2, and CH2N15N have been examined between 230 and 4000 cm—1 under medium resolution. Band positions have been measured for all the distinguishable parallel features. Nearly all of the perpendicular fundamentals have been resolved and analyzed. The [A″—½(B″+C″)] rotational constants derived are: CH2N15N, 8.747±0.015 cm—1; CD2N2, 4.253±0.01 cm—1; CHDN2, 5.72±0.1 cm—1. These data combined with that given earlier for the CH2N2isotope, show that the averaged distance of the hydrogen atoms from the molecular axis (in CH2N2 and in CH2N15N) is 0.9580±0.0006 Å and of the deuterium atoms (in CD2N2) is 0.9560±0.001 Å.
In contrast to earlier studies, we were able to find no evidence for the presence of a tautomeric form of diazomethane in the samples studied.
40(1964); http://dx.doi.org/10.1063/1.1725118View Description Hide Description
Infrared spectra of pure solid diazomethane and diazomethane in nitrogen or argon are given here for the molecules CH2N2, CD2N2, CHDN2, and CH2N15N. These data combined with the gas‐phase spectra reported earlier provide a basis for a reassignment of the vibrational spectrum. The vibrational potential function, centrifugal distortion constants, Coriolis coupling constants, and thermodynamic functions of diazomethane have been calculated. The out‐of‐plane hydrogen bending force constant is found to be unusually low, 0.045×10—11 erg rad—2. This is about one‐fifth of that for ethylene and about one‐half of that for ketene. The observed divergence of the energy levels of the out‐of‐plane hydrogen bending mode shows that there must be a large positive quartic contribution to the potential function for this motion.
40(1964); http://dx.doi.org/10.1063/1.1725119View Description Hide Description
Absorption coefficients of oxygen have been measured in the 1060–580‐Å wavelength region using a continuum background at a bandwidth of 0.5 Å. The background light source is a repetitive discharge through helium which produces the Hopfield continuum. Absorption bands and underlying dissociation and ionization continua are observed throughout this wavelength region. The continuum rises linearly from ≲20 cm—1 at the first ionization threshold (1026.7 Å), to about 300 cm—1 at 840 Å where the continuum begins to rise more sharply. Toward shorter wavelengths, there are three maxima in the continuum at about 800, 720, and 610 Å with approximate k values of 850, 850, and 1000 cm—1, respectively. The absorption bands appear diffuse, probably due to pre‐ionization, and maximum k values of up to 1700 cm—1 are found. Dissociation and ionization processes responsible for the continua are discussed, and comparison is made with previous absorption coefficient measurements.
40(1964); http://dx.doi.org/10.1063/1.1725120View Description Hide Description
The electron mobility of charge carriers in copper phthalocyanine has been determined to be approximately two orders of magnitude greater than that in metal‐free phthalocyanine. This difference can be interpreted in terms of the electron spin resonance results and the intermolecular copper‐nitrogen overlap. The electron spin resonance of copper phthalocyanine magnetically diluted in metal‐free phthalocyanine has been measured in single crystals. The hyperfine structure of the nitrogen ligands, as well as that of the copperhyperfine structure, is clearly resolved. An analysis of the data in terms of molecular orbitals suggests a scheme of strong out‐of‐plane π bonding with the π orbitals of the phthalocyanine ring and almost no in‐plane π bonding. This brings about an inversion of the usual positions of the copperEg and B 2g orbitals. This strong π bonding predicts that in metallo‐organic compounds of this type, the organic π‐electron delocalization is increased to include the central metal atom, and properties dependent on this delocalization should be altered when copper is used. The increased delocalization of the π‐electron orbitals gives rise to larger intermolecular π wavefunction overlap resulting in a greater mobility for charge carriers in copper phthalocyanine.
40(1964); http://dx.doi.org/10.1063/1.1725121View Description Hide Description
The electronic spectra of the tris‐ (dithioloxalato) complexes of Cr III and Co III are reported and interpreted in terms of the simple crystal field picture. The magnetic susceptibility of the analogous Fe III compound is reported as a function of temperature, and interpreted by means of the theory of Figgis; this leads to an estimate of the parameters describing the covalency and axial field in the compound. Dithioloxalate is not a strong ligand, in the spectrochemical sense, but it does lead to an exceptional lowering of the electron—electron repulsions of the central metal ion.
40(1964); http://dx.doi.org/10.1063/1.4755936View Description Hide Description
An analysis of the optical and magnetic properties of trivalent vanadium complexes is given on the basis of the ligand-field model. The calculation of g values and magnetic susceptibility is outlined, using eigenstates of the "zero magnetic field" Hamiltonian, including trigonal field and spin-orbit terms. This enables the results of magnetic resonance experiments to be interpreted without the use of a spin Hamiltonian, in cases where the optical spectrum has been measured. The example of vanadium corundum is discussed in some detail. The dependence of energy levels on the parameters B, C, Δ, v, v ′, and ζ is used to determine these parameters from the absorptionspectrum. Values of the magnetic constants of vanadium corundum are obtained as g ∥= 1.919, g ⊥= 1.719, and D=7.9 cm-1, in excellent agreement with previous experimental results. The paramagneticsusceptibility is predicted in the range lo-300°K.
Many‐Parameter Alternant Molecular Orbital Calculations for Large Cyclic Systems with Closed‐Shell Structure40(1964); http://dx.doi.org/10.1063/1.1725122View Description Hide Description
Computer calculations of the energies for various ring systems with closed‐shell structure have been carried out within the framework of the many‐parameter alternant molecular orbital method. A significant improvement is obtained over the corresponding single‐parameter results. Since the explicit energy minimizations are rather time consuming, some semiempirical relations between the relevant parameters are also discussed.
40(1964); http://dx.doi.org/10.1063/1.1725123View Description Hide Description
Wavefunctions for OH— and H4O++ are presented in the self‐consistent field molecular orbital approximation, using a minimum basis set of Slater‐type atomic orbitals. A wavefunction for H4O++ based on a one‐center model is also included. A comparison is made, for the isoelectronic series OH—, H2O, H3O+, H4O++ of three methods of calculating molecular energies, namely the two methods already mentioned and a valence bond method.
The changing properties of the OH bond in the series are discussed within the self‐consistent field approximation by an analysis of the electron distribution. A good correlation is found between the bond strength and the maximum in the bond of the δ function first introduced by Roux.
40(1964); http://dx.doi.org/10.1063/1.1725124View Description Hide Description
The vibrational symmetry and selection rules for an ethane‐type molecule are re‐examined. It is demonstrated that the kinetic and potential energy matrices can be fully reduced under either D 3h or D 3d . However, the dipole moment and polarizabilitytensors do not, in general, show quite as much symmetry, so that certain infrared and Raman coincidences, forbidden by D 3d selection rules, become allowed.
40(1964); http://dx.doi.org/10.1063/1.1725125View Description Hide Description
The rate at which gaseous ions neutralize each other has been measured in a variety of gases over a relatively wide pressure range. The results indicate that neutralization occurs by parallel bimolecular and termolecular processes. The rate of the termolecular process is sensitive to the nature of the inert gas in which recombination occurs. Two mechanisms for the termolecular process are discussed.