Volume 36, Issue 3, 01 February 1962
Index of content:
36(1962); http://dx.doi.org/10.1063/1.1732573View Description Hide Description
Measurements have been made of the electron spin resonancespectra of irradiated polyethylene filaments with various draw ratios. The feature of the spectra is that the doublet splitting in each component of a quintet structure depends on the degree of molecular orientation in filaments. This can be ascribed to σ‐proton anisotropy in alkyl radicals mainly trapped in irradiated polyethylene.
From the information about CH radicals of irradiatedorganic crystals and the molecular orientation of polymers, the relation between the doublet splitting D and the degree of molecular orientation f is obtained as follows:for the high‐density polyethylene, consisting predominantly of the crystalline regions, and the spin density of the central carbon atom of the radical is 0.70.
36(1962); http://dx.doi.org/10.1063/1.1732574View Description Hide Description
Quantitative calculations of the absorption frequency, transition moment length, and polarization of the first strong absorption band in the series of compounds C6H5N=N(C6H4N=N) x C6H5 have been successfully carried out using a model employing delocalization of electronic excitation energy rather than delocalization of electrons. It is found that the compounds can be treated as azo‐perturbed phenyl groups interacting with both an electrostatic force and through conjugation. Because of the electrostatic part of the interaction, there results a demonstrable heat of single bond isomerization in phenylazo‐β‐naphthalene, its conformational isomers possessing different colorband spectra.
The n—π* transition in the azo dyes is shown to be, in all probability, the low‐frequency component of two previously degenerate n—π* bands which have split. The intensity and polarization of the formally forbidden, low‐frequency n—π* band can be explained by assuming a mixing of the n—π* band with the strong, low‐frequency band responsible for the color in azo dyes.
A high‐frequency band found at 44 kk (the symbol kk used throughout this paper stands for kilokayser or 103 cm—1) having a constant intensity throughout the series of dyes investigated has been shown to be isolated within the end phenyl groups.
Effect of Temperature on the Structure of Gaseous Molecules. Molecular Structure of PCl3 at 300° and 505°K36(1962); http://dx.doi.org/10.1063/1.1732575View Description Hide Description
The molecular structure of PCl3 has been studied by electron diffraction from the vapor at nozzle temperatures of 300° and 505°K. Both the size of the molecule and the displacement of the atoms during molecular vibration are found to be significantly greater at the higher temperature: The P–Cl and Cl···Cl distances are longer by 0.3 and 0.4%, respectively, and the rms amplitudes associated with these distances are greater by a striking 19 and 31%. Both the increased size of the molecule and increased amplitudes are in very good agreement with prediction from simple theory. The results at 300° and 505°K, respectively, are r P‐Cl=2.039±0.0014 A and 2.045±0.0016 A; r Cl···Cl=3.130±0.0026 A and 3.142±0.0038 A; <Cl–P–Cl=100.27±0.09° and 100.40±0.16°; l P‐Cl=0.0501±0.0013 A and 0.0594±0.0017 A; l Cl···Cl=0.0834±0.0023 A and 0.1097±0.0035 A. The interatomic distances given are ra values obtained from the third cycle of least‐squares refinement of intensity curves and differ from the equilibrium values re by small amounts; the lij values differ similarly from the le values. The estimated standard errors include standard deviations derived from the least‐squares procedure, estimates of correlation among the data, uncertainty in the constants of the experiment, and uncertainty in the factors employed in the data reduction.
36(1962); http://dx.doi.org/10.1063/1.1732576View Description Hide Description
Using the mean square amplitudes of vibration obtained from gaseous electron diffraction experiments at 300° and 505°K together with the normal vibration frequencies, a reasonable set of values has been derived for the potential constants of the general quadratic function The values in millidynes/A are, with estimated standard errors, .
36(1962); http://dx.doi.org/10.1063/1.1732577View Description Hide Description
By the use of projection operators a series of approximations to the perturbed problem is generated, the first of which turns out to be the second‐order Brillouin‐Wigner theory. This connection is used to show that the latter is in certain cases either an upper or a lower bound to the correct energy.
36(1962); http://dx.doi.org/10.1063/1.1732578View Description Hide Description
The direct photolyses of CH2CD2 and trans‐CHDCHD were carried out at room temperature in the vacuum ultraviolet region. Kr, Xe, and Hg resonance radiations were used for photolyses. Products at the Kr lines were mainly hydrogen, acetylene, ethane, and n‐butane. The ratio of acetylene/hydrogen was 2.8±0.2 at 1236 A. The photolysis of CH2CD2 gives 40% H2, 40% HD, and 20% D2. The acetylene was 12% C2H2, 62% C2HD and 26% C2D2. The relative amounts of H2, HD and D2 depend upon whether a hydrogen molecule is eliminated from two (type I process) or one (type II process) carbon atom. The remaining vinylidene rapidly rearranges to acetylene.
The photolysis of trans‐CHDCHD gives 17% H2, 73% HD, and 10% D2. This shows that hydrogen is formed from the trans as well as from the cis position and that the isotope effect for the type I process is slightly smaller than that for the type II process. Nearly free rotation of the molecule in its excited state is suggested. The percentages of the hydrogen isotopes produced are almost independent of exciting wavelength in both isotopic ethylenes. A comparison is made with Hg(3 P 1)‐sensitized photolysis.
Vacuum Ultraviolet Photochemistry. III. Primary Processes in the Vacuum Ultraviolet Photolysis of Water and Ammonia36(1962); http://dx.doi.org/10.1063/1.1732579View Description Hide Description
Water and ammonia have each been photolyzed in the absence and presence of C2D4 which served to scavenge H atoms. Wavelengths used were: for ammonia, 1849 and 1236 A; for water, 1236 A. Under conditions where H atoms are efficiently scavenged by C2D4, the production of H2 signifies a primary photochemical process giving molecular H2 directly. It is found that at 1849 A, ammonia decomposes almost entirely to H+NH2. At 1236 A, two primary processes are observed.Process (a) is about ⅙ as probable as process (b). At 1236 A, the photolysis of water proceeds via two primary processes.The probability of process (c) being three times that of process (d). It is suggested that primary process (d) constitutes a reasonable photochemical mechanism for hydrogen formation in the earth's upper atmosphere.
36(1962); http://dx.doi.org/10.1063/1.1732580View Description Hide Description
An attempt was made to determine the absorption coefficient δ a for electrons incident on MgO and irradiated MgO for the impacting energy range, 0.2 ev through the conduction band (about 7.3 ev). It was found that electron trapping was so severe that the crystals would not thermally discharge at temperatures below 350°C. Consequently, the charged crystals were neutralized by a less satisfactory technique, high energy electron bombardment. δ a was reproducible only at energies less than 4 ev. Sharp slope changes were observed at about 1.80 and 3.00 ev. These ``lines'' correspond to luminescence spectra obtained for catalytic recombination of N on MgO. Since slow electrons have been observed to interact predominantly with crystal defects, the data support the suggestion that defects can play a dominant role in catalytic reactions.
36(1962); http://dx.doi.org/10.1063/1.1732581View Description Hide Description
The infrared spectrum of sulfur trioxide was obtained under prism resolution in the gaseous state and in xenon matrices at liquid‐nitrogen temperature. In both cases a satisfactory vibrational assignment of the monomeric SO3spectrum could be made on the basis of a simple D 3h symmetry model. The observed gas phase fundamentals were v 3(e′) = 1391, v 4(e′) = 529, and v 2(a 2″) = 495 cm—1. The matrix fundamentals were essentially the same as those of the gas phase except that the v 2(a 2″) mode was shifted to 464 cm—1. A normal coordinate treatment of the SO3 molecule was carried out and potential constants were determined for both Urey‐Bradley and simplified valence force fields. Three weak absorption bands of S3O9 were also detected in the gas‐phase spectrum. From the temperature and pressure variation of the intensities of these bands it was estimated that for the trimerization reaction at 298°K, Kp was approximately 1 atm—2 and ΔH 298° was approximately 30 kcal/mole of S3O9. The values of the thermodynamic properties of monomeric SO3 were computed for the ideal gaseous state using the rigid rotor harmonic oscillator approximation at 1 atm from 100° to 1500°K.
36(1962); http://dx.doi.org/10.1063/1.1732582View Description Hide Description
The reaction rate has been calculated for a vibrationally excited diatomic molecule to be de‐excited by collision with another atom or molecule, the second particle carrying away the excess vibrational energy as kinetic energy. The quantum mechanical distorted wave method has been used in the ``modified wave number'' approximation, and the large amplitude of the vibrational motion is taken into account both in the choice of vibrational wave functions (Morse functions) and in the interaction potential. The calculation is performed for the processfor the vibrational transitions v = 5 to v′ = 4, 3, 2, 1, 0, and for v = 2 to v′ = 0 and v = 1 to v′ = 0, for the temperature range 300–6000°K. The results show clearly that in a situation of this kind the collisional de‐excitation of the molecular vibration proceeds in steps v—v′ = δv = 1, rather than δv>1.
36(1962); http://dx.doi.org/10.1063/1.1732583View Description Hide Description
Electron affinities of negative atomic ions were obtained in a previous paper [H. R. Johnson and F. Rohrlich, J. Chem. Phys. 30, 1608 (1959)] by isoelectronic extrapolation using a four‐term approximation formula. Recently, Edlén [B. Edlén, J. Chem. Phys. 33, 98 (1960)] simplified this procedure, using only three terms and improved experimental input data. The theoretical justification of this procedure lies in the assumption that these formulas are the beginning terms of a perturbation series which is at least semiconvergent. Therefore, a four‐term formula should give better results than a three‐term formula. It is shown here that the experiments indicate that this is not likely to be the case, thereby raising strong doubts about the justification of this method.
An alternative method is therefore suggested. Here, the regularity pattern of the ionization potentials as a function of Z (fixed degree of ionization) is extrapolated. This is therefore an extrapolation of the results of a ``horizontal analysis.'' The method requires one experimental affinity for each p shell as long as sufficiently precise data on ionization potentials of highly ionized atoms (fourth and higher spectrum) are not available. The results agree within experimental error, except for the most recent value of C— which is about 10% too low.
36(1962); http://dx.doi.org/10.1063/1.1732584View Description Hide Description
The motion of small suspended particles in a gas or gas mixture containing gradients of temperature, pressure, or composition is derived as a special case of the Chapman‐Enskog kinetic theory of gases, by formally treating the suspended particles as large molecules. Gas molecules colliding with the suspended particles are considered to rebound elastically, but a fraction f rebound in random directions and the remainder rebound specularly. The results check, in an indirect way, the calculations of Waldmann by a momentum transfer method on a slightly different model, in which the randomly rebounding molecules also have a random distribution of speeds. Significantly different results are predicted by the two models only in the presence of a temperature gradient (thermal diffusion), which has interesting implications concerning thermal diffusion in polyatomic gases.
36(1962); http://dx.doi.org/10.1063/1.1732585View Description Hide Description
The absorptionspectrum of VCl4 vapor from 400 to 23 000 cm—1 was determined. A system of bands with maximum absorption coefficient at 9000 cm—1 is attributed to ligand field splitting of the 2 D ground term of the free V (V) ion. The three‐component structure of this band is attributed to Jahn‐Teller splitting of the excited state. Simple calculations of the expected splitting are offered in support of this assignment.
36(1962); http://dx.doi.org/10.1063/1.1732586View Description Hide Description
A method used previously for obtaining the departure from steady‐state kinetics with one reactive intermediate is extended to chain reactions with two or more intermediates or radicals. This method is applied to the H2–Br2reaction and to the pyrolyses of methane, ethane, and acetaldehyde. It is found that serious departures from steady‐state conditions occur in the experimental range of ethane decomposition and H2—Br2reaction. The departure is serious for all such processes in the very fast reaction, high‐temperature region.
Using a hypothetical reaction scheme with characteristics similar to those of most chain reactions, approximate equations are obtained for the initial transients connected with the build up of radicals. The relationship between steady‐state departure, both during and after the transient period, and the cumulative extent of reaction are explored for this reaction.
36(1962); http://dx.doi.org/10.1063/1.1732587View Description Hide Description
The energy levels of a rigid asymmetric rotor containing one or more quadrupolar nuclei and subject to an electric field are discussed for the case in which the Stark effect energies are larger than those arising from quadrupole coupling effects.
The theory is applied to quantitative Stark effect measurements on COCl2 35 and CH2CCl2 35. The dipole moments determined by this method are 1.17 and 1.34D, respectively.
Theory of the Anomalous Heat Capacity in Solid Hydrogen and Deuterium at Low o‐Hydrogen and p‐Deuterium Concentration36(1962); http://dx.doi.org/10.1063/1.1732588View Description Hide Description
The theory of the anomalous heat capacity for low concentrations of ortho hydrogen in the solid state has been extended by a calculation based on the angular potential energy between adjacent molecules. The effects included were (1) the chemical or valence energy, (2) the electrostatic quadrupole‐quadrupole energy, and (3) the inverse sixth‐power dispersion energy. The expression used for the first type of interaction was derived theoretically by de Boer, while gas‐phase experimental parameters were used to evaluate the second two types of interaction in connection with a theoretical estimate of the anisotropy of polarizability of the hydrogen molecule.
It was found that only electrostatic quadrupole‐quadrupole interactions had to be considered at one atmosphere, but at higher pressures, the valence forces became important. The case of three ortho hydrogen molecules in a row was also treated in the quadrupole approximation. The heat capacity predicted by this model was somewhat different from that predicted for isolated ortho‐ortho pairs. The theory was compared with available one atmosphere data on ortho hydrogen and para deuterium at low concentrations in the solid. The results depend not only on the total ortho concentration but also on the relative concentrations of isolated ortho molecules, isolated pairs of ortho molecules, and more complicated configurations. Nakamura's suggestion (that an additional term in the anomalous heat capacity proportional to the ortho concentration is needed to explain the data) seems to be supported by the analysis, although additional data would be desirable.
36(1962); http://dx.doi.org/10.1063/1.1732589View Description Hide Description
The equilibrium, B2O3(c, 1) + BF3(g) = (BOF)3(g), was studied in the temperature range of 330–1000°K by means of transpiration. The heat of reaction employing crystalline B2O3 was found to be 7.6 kcal/mole; while the liquid B2O3 yielded a ΔHr of 2.4 kcal/mole. These lead to a value of —567.8±0.5 kcal/mole for ΔH f298°K of (BOF)3(g) and a value of 88.7±2 cal/deg/mole for S 298 of (BOF)3(g). Partial pressure studies employing mixtures of argon and BF3 indicated that dissociation of the trimer (BOF)3(g) is negligible in the temperature range investigated.
36(1962); http://dx.doi.org/10.1063/1.1732590View Description Hide Description
Reversible changes due to gas adsorption in spectra of powdered zinc oxide were observed. In the range 2000∼1200 cm—1, CO2 gave increases in absorption at 1640 and 1430 cm—1 on adsorption at 20°C and at 1570 and 1380 cm—1 at 200°C. These results could be interpreted by assuming that CO2 adsorbed at 20°C is combined with surface oxygen, but that at 200°C bonded to surface zinc. Another change, a decrease in the conduction‐electron absorption of the solid, was found in the case of adsorption at 200°C. Similar decreases by adsorption of O2, C2H4, and H2 (of opposite sign) are reported. Correlation between the adsorbed state of CO2 and influences of the adsorption on electrons in the solid is discussed. Some data on adsorption velocities and adsorbed quantities of CO2 are given.
36(1962); http://dx.doi.org/10.1063/1.1732591View Description Hide Description
The photostationary concentration of ions in gaseous nitric oxide has been measured using a Langmuir probe. The ion concentration depends on the square root of the ion production rate, which indicates that ions and electrons disappear predominately by dissociative recombination. In addition, the rate of decay of the electron concentration in the gas after interruption of the ionizing radiation has been measured. The data indicate that the ion‐electron dissociative recombination rate constant is no greater than 2×10—6 cm3/ion sec, and may be as low as 4×10—7 cm3/ion sec.
Mass Spectrometry of Ions in Glow Discharges. I. Apparatus and Its Application to the Positive Column in Rare Gases36(1962); http://dx.doi.org/10.1063/1.1732592View Description Hide Description
An apparatus is described which samples and analyzes ions from a glow discharge. Results are given for the positive column of discharges in argon, krypton, and mixtures of the two, at pressures between 0.4 and 1.0 mm and current densities in the range 0.035 to 0.105 ma/cm2. In general, the results are in reasonable agreement with those of other workers, but some differences are noted.
The results appear to favor the formation of A2 + by the reaction Ar*+Ar→A2 ++e, but it is not possible to rule out conclusively the three‐body process Ar++2Ar→Ar2 ++Ar. Traces of hydrogenous impurities (especially water) appear to interfere with molecule ion formation.
The formation of ArH+ from impurities is also studied and the results suggest that it may be formed from any or all of Ar+, Ar2 + or Ar*. Experiments in which 1.25% hydrogen is added to the argon suggest that ArH+ is not formed mainly by the reaction of Ar+ with H2 but that the reaction of metastable argon atoms with hydrogen atoms should be seriously considered.
The visible structure of a striated positive column is found to be reflected in the ion concentrations which vary differently for different ions. The effect seems to be related to fluctuations in the potential gradient which may be enhanced by the formation of negative ions.