Volume 42, Issue 3, 01 February 1965
Index of content:
42(1965); http://dx.doi.org/10.1063/1.1696065View Description Hide Description
The Raman and infrared spectra of crystalline CS2 have been observed at low temperatures. The Raman band 2ν2 and the infrared band ν3 have been found to split into two components, while no splitting has been seen for the Raman band ν1. That the rule of mutual exclusion holds for the Raman and infrared spectra of crystalline CS2 indicates the inversion symmetry of the molecule is preserved even in the crystal. A dipole—dipole coupling model for the intermolecular interactions in the crystal explains the band splitting.
Two low‐frequency Raman bands have been observed and assigned to the lattice vibrations of rotational mode.
42(1965); http://dx.doi.org/10.1063/1.1696066View Description Hide Description
The secondary spectra arising from ionic reactions in propane at several mean ion energies are reported. The results are compared with computed values taken from results obtained by the elegant techniques developed by Lindholm. From the comparison a calculation is made for the secondary spectrum obtained by bombarding C3H8 with C2H4 + ions. Experiments using mixtures of C2D4 and C3H8 lead to an observed secondary‐ion spectrum which is in good agreement with that calculated. A significant number of ionic fragments in the secondary spectrum appear to be formed by endothermic processes. It is assumed that translational energy supplies the required energy. Some appearance‐potential measurements support this assumption. There appears to be some evidence for CH3 — transfer when C3H8 is bombarded either by C2H5 + or C2H4 +. In both cases there is also a competing H— transfer process.
42(1965); http://dx.doi.org/10.1063/1.1696067View Description Hide Description
The specific reaction rates for reactions between ions and molecules when both the reacting partners have thermal energy only have been determined for several systems. These rates have been determined by using a combination of a pulsed ionizing beam followed by a variable time‐delay ion‐extraction pulse. The results are compared with the field strength dependent values obtained in the same source operated in the conventional manner. The apparent thermal rate constant for the reaction CH4 ++CH4→CH5 ++CH3 is 9.6×10−10 cm3 molecule−1 sec−1, but after correction is made for detector discrimination, the value becomes 17.0×10−10 cm3 molecule−1 sec−1. For the field strength dependent values the magnitude of the ionizing current has a strong effect upon the observed specific reaction rate. Operation under conditions where the ionizing current is 0.1 μA led to reproducible values for the specific reaction rates.
42(1965); http://dx.doi.org/10.1063/1.1696068View Description Hide Description
Although neither hydrazine nor water supercool to a large extent, their mixtures do. Aqueous solutions of hydrazine may be strongly supercooled and stabilized as rigid glasses. The values of the glass‐transformation temperatures determined during warmup depend on the warmup rate, permitting the evaluation of mean values of the relaxation times characterizing the motions that are frozen in below such temperatures. The supercooled mixtures crystallize during warmup at temperatures that also depend on the warmup rate. The duration of the crystallization process exhibits a one‐to‐one correspondence with the temperature at which it occurs. The logarithm of the process duration varies linearly with the inverse of the absolute temperature permitting the evaluation of activation energies. Application of the theory of absolute reaction rates leads to the determination of entropy barriers. The correlation observed with the equilibrium phase transformations permits an interpretation of the processes of supercooling and crystallization during warmup. Detailed experimental results are discussed.
Entropy, Internal Energy, and Heat Capacity of MnCl2 between 0° and 4.2°K in Magnetic Fields to 100 kG42(1965); http://dx.doi.org/10.1063/1.1696069View Description Hide Description
The thermodynamically reversible isothermal change of entropy of MnCl2 with magnetic field directed along the b magnetic axis has been measured calorimetrically. At 1.498°K (∂S/∂H)T is positive below 7.5 kG, then negative to magnetic saturation. At 1.333°K, (∂S/∂H)T is negative below 4.5 kG, then positive to 9.25 kG, after which it is negative to saturation. The isothermal entropy change with field has also been measured by a two‐step process, in which: (1) the internal‐energy change was obtained by combining calorimetric measurements with irreversible magnetic work; (2) combining the internal‐energy change with reversible measurements of magnetic work. Measurements of heat capacity in constant fields have been repeated to improve accuracy and to apply a severe test of magnetothermodynamic reversibility by series of measurements made after varied approaches to the starting conditions. The entropy, internal energy, and heat content have been given over the range 0–4.2°K and 0–100 kG, and there are evidently no transition points in the entire area investigated, although gradual changes in magnetic structural types undoubtedly occur. Some values of the heat capacity at constant magnetic moment have been calculated.
42(1965); http://dx.doi.org/10.1063/1.1696070View Description Hide Description
An electron diffraction structure determination for ethane and deuteroethane has been carried out to study the magnitudes of primary and secondary deuterium isotope effects on bond lengths. Mean parameters and estimated standard errors for C2H6 were rg (C–H) = 1.1122±0.0012 Å, lg (C–H) = 0.0760±0.0010 Å, rg (C–C) = 1.5340±0.0011 Å, lg (C–C) = 0.0496±0.0010 Å, and ∠CCH = 111.0±0.2°. Corresponding parameters for C2D6 were rg (C—D) = 1.1071±0.0012 Å, lg (C—D) = 0.0668±0.0010 Å, rg (C–C) = 1.5323±0.0011 Å, lg (C–C) = 0.0517±0.0010 Å and ∠CCD = 111.0±0.2°. Shrinkage corrections have not been made for bond angles. A primary deuterium isotope effect of 0.0050±0.0006 Å was found for the carbonhydrogen bond. A possibly significant secondary effect was observed in which the C–C length in ethane exceeded that in deuteroethane by Δrg (1) = 0.0016±0.0007 Å. Some aspects of secondary isotope effects are discussed briefly.
42(1965); http://dx.doi.org/10.1063/1.1696071View Description Hide Description
The infrared spectrum of NO2, suspended in oxygen and argon matrices at helium temperature, is described. The spectra are similar to those previously reported, but many new absorptions are observed as well. The absorptions are assigned among the molecular species NO2, stable N2O4, and three unstable forms of N2O4.
42(1965); http://dx.doi.org/10.1063/1.1696072View Description Hide Description
Paramagnetic resonance measurements are reported in solid solutions of quinoline, and of isoquinoline in durene under irradiation with ultraviolet light at 77°K. The fine structure of the magnetic resonancespectrum observed at 9.2 Gc/sec may be described by the spin Hamiltonian, with S = 1. D, E, and the principal values of g are reported for each molecule. The principal axis systems of the zero‐field tensorsD are found to be displaced from the molecular axis system of durene in the host crystal in both the quinoline and isoquinoline doped crystals. The D axis systems are found to be rotated about an axis perpendicular to the molecular plane of durene. The principal axis systems of D and g are found to be the same within experimental error for the quinoline phosphorescent state. Hyperfine structure is observed in both molecules, and is assigned to coupling with protons in the 1, 4, 5, and 8 ring positions in quinoline, and in the 1, 4, 5, and 8 ring positions in isoquinoline. The normalized spin density at these positions is approximately equal to 0.23 in both molecules, assuming that the hyperfine coupling tensors for doublet‐state π radicals are applicable to triplet‐state molecules.
The phosphorescent states of quinoline and isoquinoline are interpreted to result from π—π* excitations. The decay constants of the isomers were found to be 0.80±0.02 and 0.95±0.1 sec, respectively.
Preliminary measurements on the phosphorescent state of cinnoline are consistent with the interpretation of this as an n—π* triplet state.
42(1965); http://dx.doi.org/10.1063/1.1696073View Description Hide Description
Thermal diffusion column transport coefficients were measured for mass 28—mass 29 carbon monoxide in a 7.32 m long, hot‐wire column. The three coefficients which characterize column performance were independently evaluated at wire temperatures of 350° and 500°C from the results of both static and flow separation experiments at various pressures. If the value of the thermal diffusion factor at 288°K for carbon monoxide is assumed to be 0.0054, good agreement is obtained between the experimental coefficients and those predicted from existing theory with shape factor integrals based on the Lennard‐Jones 12–6 potential.
42(1965); http://dx.doi.org/10.1063/1.1696074View Description Hide Description
Yttrium chloride is monoclinic with C 2 point symmetry at the site of a Y3+ ion. The point symmetry is approximately octahedral. The absorption and fluorescence spectra of Er3+ in YCl3 are used to find the energy levels of Er3+. The Zeeman effect and the excitation of fluorescence are studied. Assuming a cubic field, the Stark splittings of the Z and Y groups are used to obtain the crystalline field parameters:
The cubic field gives approximate agreement with the experimental data and explains the clustering of Stark components which is characteristic of rare‐earth ions in YCl3. The total Stark splitting of the free ion levels of a rare‐earth ion is larger in YCl3 than in LaCl3. The centers of gravity of the excited levels of Er3+ are higher in LaCl3 than in YCl3, and this shift increases with increasing wavenumber.
42(1965); http://dx.doi.org/10.1063/1.1696075View Description Hide Description
Compact formulas are derived for one‐ and two‐electron multicenter energy integrals between an orthogonal basis of isotropic harmonic oscillator (Gaussian) functions in Cartesian coordinates. Up to four centers are considered. Overlap and kinetic energy integrals are given in closed form, but the potential energy integrals require a one‐dimensional numerical quadrature. A technique due to Smirnov was used to obtain all formulas.
42(1965); http://dx.doi.org/10.1063/1.1696076View Description Hide Description
The TaO and TaO2 molecules vaporizing from tantalum oxide at 2270°K have been trapped in neon and argon matrices at 4° and 20°K and studied spectroscopically in the infrared, visible, and near‐ultraviolet regions. TaO spectra exhibit the three electronic transitions observed in the gas and analyzed by Premaswarup and Barrow. The matrix spectra lead to a probable revision of the 4155 Å gas transition, indicating that TaO has a 2Δ r ground state. In all, 16 electronic transitions from the X level have been distinguished by 18O substitution and most of the upper‐state vibrational frequencies determined. Two electronic transitions of TaO2 in a neon matrix occur at 8607 Å (strong) and 6159 Å (weak). The bending frequency in the upper state dominates both of the band systems and indicates that the O–Ta–O angle undergoes a large change in the transitions. The infrared spectrum of TaO2 exhibits two bands, suggesting that the molecule is bent in the ground state. Vibrational frequencies in the ground state are assigned as follows: TaO, 1020 cm−1 (corroborating the gas value); TaO2, v 1″=971 cm−1, v 2″=?, v 3″=912 cm−1. A molecular orbital scheme for each of these molecules is proposed leading to X 2Δ r for TaO and X 2 B 1 for TaO2.
42(1965); http://dx.doi.org/10.1063/1.1696077View Description Hide Description
Matrix elements which are diagonal with respect to the cubic field are given for the crystal‐field and spin—orbit Hamiltonians for the transition metald‐electron configurations. A multiplication factor, the free‐ion reduced matrix element, is not included in the tables given.
42(1965); http://dx.doi.org/10.1063/1.1696078View Description Hide Description
The crystal structures at 298°K of MnCl2·2H2O and FeCl2·2H2O have been refined by means of three‐dimensional differential syntheses using diffractometer single‐crystal x‐ray‐intensity data. The crystal structures of these isomorphic compounds consist of polymeric chains of metal and chlorine ions arranged in a near‐square planar configuration with each chlorine ion shared by two metal ions. The water molecules which fill the remaining octahedral positions about the metal ion link adjacent chains, paralleling the c axis, by hydrogen bonds.
42(1965); http://dx.doi.org/10.1063/1.1696079View Description Hide Description
The infrared (400–4000‐cm−1) and ultraviolet (5000–2200‐Å) absorption spectra of NiF2 and NiCl2 molecules isolated in an Ar matrix at 14°K have been observed. Sharp systems of absorptions near 780 cm−1 for NiF2 and 520 cm−1 for NiCl2 can be assigned to the antisymmetric stretching fundamental of the isolated molecules. Most of the vibrational splittings of the more abundant isotopic species have been resolved. Absorptions due to dimers and to other as yet uncharacterized species also appear. Evidence supports the hypothesis that NiF2 and NiCl2 are linear. No ultraviolet absorptions have been observed for NiF2, but the intense absorption previously observed for NiCl2 between 3650 and 2750 Å has been found to have extensive vibrational structure, probably contributed by the symmetric stretching mode of the upper state.
42(1965); http://dx.doi.org/10.1063/1.1696080View Description Hide Description
Accurate values of the parallel and perpendicular components of g‐factor and hyperfine coupling tensor were determined for [CrOCl n ]—(n−3) where n=4 and 5, by the ESR line shape analysis. It was shown by a molecular orbital treatment that these magnetic parameters can be explained consistently by taking into account of an excited electronic configuration in which an electron in a filled orbital is excited to the half‐filled level. An assignment of a hitherto unexplained visible absorption band was proposed on the same ground.
Molecular Vibrations of Quinones. II. Infrared Spectra (Solution and Vapor) of p‐Benzoquinone and p‐Benzoquinone‐d 442(1965); http://dx.doi.org/10.1063/1.1696081View Description Hide Description
Infrared spectra of quinone and quinone‐d 4 have been obtained for both vapor phase (4000–650 cm−1) and solution (4000–75 cm−1). The vapor spectra are analyzed in terms of the band contours expected for transitions polarized along the three axes corresponding to the principal moments of inertia.
Molecular Vibrations of Quinones. III. Preparation and Infrared Spectra (Solution and Vapor) of p‐Benzoquinone‐d 1, p‐Benzoquinone‐2,5‐d 2, p‐Benzoquinone‐2,6‐d 2, p‐Benzoquinone‐18O2, and p‐Benzoquinone‐d 4‐18O242(1965); http://dx.doi.org/10.1063/1.1696082View Description Hide Description
Three specifically deuterated quinones, p‐benzoquinone‐d 1, ‐2,5‐d 2, and ‐2,6‐d 2, have been prepared by a scheme involving (1) the formation of the dibenzyl ether of the appropriate bromohydroquinone, (2) reaction of this bromoether with n‐butyl lithium, (3) introduction of deuterium by solvolysis of the lithium derivative in D2O, (4) cleavage of the ether with sodium in liquid ammonia, and (5) oxidation of the specifically deuterated hydroquinone by chromic oxide in buffered acetic acid.Infrared spectra have been obtained for the three compounds both in solution (4000–75 cm−1) and in vapor phase (4000–300 cm−1). The band contours of the vapor spectra are analyzed and discussed.
In addition, p‐benzoquinone‐18O2 and quinone‐d 4‐18O2 have been prepared by exchange of quinone and quinone‐d 4 with H2 18O. Solution spectra (4000–300 cm−1) are reported.
Molecular Vibrations of Quinones. IV. Raman Spectra of p‐Benzoquinone and Its Centrosymmetrically Substituted Isotopic Derivatives and Assignment of Observed Frequencies42(1965); http://dx.doi.org/10.1063/1.1696083View Description Hide Description
The Raman spectra of p‐benzoquinone, quinone‐d 4, quinone‐18O2, quinone‐d 4‐18O2, and quinone‐2,5‐d 2, excited by the helium radiation 5875.6 Å, are reported, together with semiquantitative measurements of the intensities and qualitative observations on the state of polarization of the Raman shifts. The results are fully consistent with the D 2h symmetry of the four molecular species mentioned first, the last one belonging to the point group C 2h . A tentative assignment for all Raman‐active fundamental vibrational modes of the investigated compounds is given.
Molecular Vibrations of Quinones. V. Normal Coordinate Analysis of p‐Benzoquinone and Its Isotopic Derivatives42(1965); http://dx.doi.org/10.1063/1.1696084View Description Hide Description
The frequencies of the normal vibrations of ordinary, monodeutero‐, 2,5‐dideutero‐, 2,6‐dideutero‐, and tetradeutero‐p‐benzoquinone as well as ordinary and tetradeutero‐p‐benzoquinone‐18O2 have been calculated by using a quadratic potential function of the valence‐force field type with all the important cross terms. For the out‐of‐plane vibrations, Anno and Sadô's force constants have been used. For the planar vibrations, two sets of force constants have been tried. One of the sets was obtained from the force constants in benzene, hexafluorobenzene and ethylene with proper considerations and modifications. In the second set, the diagonal and off‐diagonal constants among the CC and the CO stretches have been obtained by the method of Coulson and Longuet‐Higgins, the other constants being the same as in the first set. Further calculations have been tried in order to improve the results by adjusting a few of the force constants in such a way that some of the frequencies well established by experiment are reproduced by the calculation. Only the results for ordinary and tetradeutero‐p‐benzoquinone are given in the present paper; the results for other isotopic quinones are tabulated in Part VI of this series, in which the assignment of vibrational frequencies to modes of vibrations is discussed.