Volume 41, Issue 5, 01 September 1964
Index of content:
41(1964); http://dx.doi.org/10.1063/1.1726047View Description Hide Description
By a method developed earlier, the second quantum correction to the phase shift in a collision between particles with spherically symmetric potentials is obtained. This expression, along with the classical limit and the first quantum correction developed earlier, is used to obtain the classical limit and the first and second quantum corrections to the transport cross sections Q (1) and Q (2). In these expressions the potential function is not restricted to monotonic functions; the results apply to a potential with an attractive minimum.
41(1964); http://dx.doi.org/10.1063/1.1726048View Description Hide Description
Diimide has been prepared by decomposition of hydrazine with a microwavedischarge, and the infrared spectrum of the solid and gas obtained. The spectrum of the solid at liquid nitrogen temperature agrees with the planar structure predicted for diimide, and the molecule appears to be principally in the cis form. Frequency assignments of the observed bands have been made. The structure of the molecule in the gaseous state cannot be unambiguously determined from the spectrum.
41(1964); http://dx.doi.org/10.1063/1.1726049View Description Hide Description
The elastic and reactive scattering of K by HCl and HI has been measured at several relative energies in experiments with crossed molecular beams. The interpretation follows that presented previously for K+HBr, with some improvements. For both systems the measurements on K show rainbow scattering, and from it parameters have been calculated for the exp‐six potential. From the elasticscattering at large angles and a two‐body model for it, the probability of reaction is deduced as a function of the potential energy at the distance of closest approach of the reactants.
For K+HCl the potential parameters are ε=0.45±0.02 kcal/mole and rm =3.2±0.3 Å for α=12 (assumed). The activation energy is 0.55±0.1 kcal/mole, as determined from the threshold of the probability of reaction, and is probably just the change in zero‐point energy for this endothermic reaction. There are indications that the probability of reaction increases when the potential energy is sufficient for the product KCl to be formed in excited vibrational states. The application of the two‐body model at the thresholds of formation of KCl allows another determination of rm which is in good agreement with the value obtained from the rainbow scattering. The total reaction cross section as obtained from the probability of reaction is 3.9 Å2 at Ē=2 kcal/mole. No measurements could be made on KCl.
For K+HI the potential parameters are ε=0.67±0.02 kcal/mole and rm =4.2±0.2 Å for α=12 (assumed). The activation energy of this exothermic reaction is 0.2±0.1 kcal/mole as determined from the threshold of the probability of reaction. The total reaction cross section as a function of relative energy has been obtained from measurements on KI and from the probability of reaction deduced from the elasticscattering. These two measures of the amount of KI produced agree within a factor of 2, which is the reproducibility of the measurements on KI. At a relative energy of 2 kcal/mole the total reaction cross section is 28 Å2.
41(1964); http://dx.doi.org/10.1063/1.1726050View Description Hide Description
The term E 3, proportional to the cube of the density in an expansion of the internal energy in powers of the density, has been evaluated for the Percus—Yevick, hyperchain, Born—Green—Yvon, Kirkwood, and Meeron equations. The potential used is a square well having a hard‐core diameter a and an attractive diameter 2a. A certain thermodynamic requirement of the E 3 is investigated and it is found that the hyperchain, Born—Green—Yvon, and Meeron equations give the best result, in contrast to fourth virial coefficient studies, in which the Percus—Yevick equation gives the best result. On the basis of these calculations, it seems that the use of virial expansions are of little use in the elucidation of the relative merits of liquid theories.
41(1964); http://dx.doi.org/10.1063/1.1726051View Description Hide Description
A low‐temperature infrared study of the photolysis products of CF2N2 in inert matrices has yielded the three vibrational fundamentals of the species CF2, at 668, 1102, and 1222 cm—1. Supplementary ultraviolet observations have confirmed the presence of CF2 in high concentration. Detection of the stretching fundamentals of 13CF2, present in natural abundance, has permitted an estimate of the FCF angle. The thermodynamic properties of CF2 have also been estimated. CF2 appears not to react with CO or with CO2 in a matrix environment.
41(1964); http://dx.doi.org/10.1063/1.1726052View Description Hide Description
The process of thermal evaporation has been studied on (0001) cleaved zincsurfaces. The effects on the evaporated surface structures due to zinc vapor understauration, impurities, and crystal dislocations were investigated. For undersaturation ratios between 0.29 and 0.006, evaporation proceeded primarily from localized surface regions resulting in shallow conical evaporation pits. The number density of these evaporation pits was in good agreement with the dislocation density determined by chemical etching. It was concluded that the step sources responsible for the evaporation pits were dislocations terminating at the surfaces. The theory of evaporation from dislocation sites predicts a critical undersaturation similar to that observed experimentally. The interferometrically measured evaporation‐pit slopes increased with vapor undersaturation in agreement with the theory of Cabrera and Levine near the critical undersaturation. The data extended further into the region of higher undersaturations. The effects of surface impurities were studied by admiting oxygen into the evaporation cell. For a constant vapor undersaturation, the evaporation pit slopes increased at the higher oxygen pressures. This increase could be explained qualitatively as a result of adsorbed impurities.
41(1964); http://dx.doi.org/10.1063/1.1726053View Description Hide Description
The properties of the europium benzoylacetonate laser are described in detail. The effect of an extremely high absorption constant is demonstrated by comparing outputs obtained from cells 0.47 cm and 0.10 cm in diameter. The outputs are quite different as revealed by a study of far‐ and near‐field patterns, relaxation oscillation, and spectral output. Computed and measured thresholds are compared with those of ruby crystals. Measurements of the energy output of the laser and an estimate of the losses in the resonator are reported.
41(1964); http://dx.doi.org/10.1063/1.1726054View Description Hide Description
The analysis of the absorptionspectrum of Er3+ in LaF3 is extended into the ultraviolet region to 2000 Å. A number of fluorescence lines recently observed in the region from 3000 to 25 000 Å is also reported. Based on the best over‐all agreement between the predicted ``free‐ion'' 4f 11 SLJ states and 21 experimentally observed levels for Er3+ in LaF3, one finds a set of atomic wavefunctions for the ion based on F 2 = 435.7 cm—1, F 4 = 67.21 cm—1, F 6 = 7.388 cm—1, and ζ = 2350.8 cm—1. Laser experiments are described and the details of coherent emission found at 1.61 μ are presented.
41(1964); http://dx.doi.org/10.1063/1.1726055View Description Hide Description
Polarized infrared spectra of polyacrylonitrile, poly‐α‐deuteroacrylonitrile, poly‐β,β‐dideuteroacrylonitrile and poly‐α,β,β‐trideuteroacylonitrile have been measured in the region from 4000 to 200 cm—1. β,β‐dideuteroacrylonitrile was prepared by the hydrogen re‐exchange reaction of α,β,β‐trideuteroacrylonitrile with H2O in the presence of CaO. The calculations of the normal vibrations of polyacrylonitrile and these three polydeuteroacrylonitriles have been made, assuming a syndiotactic planar zigzag chain as the most simple model for calculation. The calculation was made by the use of the GF‐matrix method with the Urey—Bradley force field. The results show fairly good agreement between the observed and calculated frequencies. The assignments of the bands are given and discussed.
41(1964); http://dx.doi.org/10.1063/1.1726056View Description Hide Description
A survey of the trends in acetone decomposition in the range from the near‐ultraviolet photolysis to gamma radiolysis has been made using a xenon discharge (1470 and 1295 Å) and a krypton discharge (1236 and 1165 Å) for room temperature photolysis. The variation of the ratios to CO of products as a function of acetone pressure and wavelength has been noted. Analysis of the mixed products from mixtures of acetone and acetone‐d 6 presents evidence for methyl radicals in the production of ethane, of hot methyl radicals in the production of methane and of hydrogen atoms in the production of hydrogen. Deviation from the H2—D2 equilibrium indicates molecular hydrogen elimination. The conclusions are confirmed by scavenger studies using propylene, iodine, and oxygen, as well as by the effects of added xenon and neon. The results are consistent with the existence of two excited states of acetone, the higher state eliminating either H or H2; the lower state, methyl. The far‐ultraviolet photolysis appears to be closer in over‐all behavior to the gamma radiolysis than to the near‐ultraviolet photolysis and the trend of the decomposition may be explained by the increase in energy of the radiation.
41(1964); http://dx.doi.org/10.1063/1.1726057View Description Hide Description
The Raman spectrum of polycrystalline methyl iodide has been studied at 77° and 195°K, and the difference between the Raman and infrared spectra has been discussed. All of six frequencies due to lattice vibrations have been found, and their assignments have been given. The heat capacity of crystalline methyl iodide at various temperatures has been calculated from the spectral data obtained and compared with the observed values of crystalline methyl bromide.
41(1964); http://dx.doi.org/10.1063/1.1726058View Description Hide Description
A variation‐perturbation method is employed for the calculation of the magnetic shieldingtensor for the nuclei of a series of diatomic molecules (H2, Li2, N2, F2, LiH, HF, LiF). The SCF—LCAO—MO functions of Ransil are used as unperturbed solutions and polynomials are introduced to represent the orbital perturbations. For certain nuclei (e.g., F in HF, N in N2), special perturbation functions are required to account for the pi‐orbital nodes. Although no total shielding measurements are available, the paramagnetic contributions can be compared with those calculated from spin—rotational constants. Good agreement is found for H2, H in LiH and HF, Li and F in LiF, but larger errors appear for the other nuclei. Estimates for the shielding anisotropy Δσ N and average shielding 〈σ N 〉 of some of the nuclei are given that should be accurate to ±10%. Since relative chemical shifts for H, Li, and F in several molecules can be obtained from these results, some experimental tests of the theory by standard NMR measurements are possible.
41(1964); http://dx.doi.org/10.1063/1.1726059View Description Hide Description
The formulation and results of a dynamical quasiclassical calculation of the reactive scattering of K+CH3I to yield KI+CH3 are reported. With a Blais—Bunker interaction potential UB and the approximation that the CH3 group can be treated as a single atom, Hamilton's equations of motion are solved to determine collision trajectories as a function of initial conditions. By appropriate Monte Carlo averaging over certain of the initial variables, the desired attributes of the reactive scattering are evaluated; these include the total reaction cross sectionSr, the differential reaction cross section σ r (Θ), the partitioning of the exothermicity of the reaction among the degrees of freedom of the products, and the distribution of angular momentum between the products molecule (J′) and relative orbital motion (L′). A detailed examination is made of the relation between the results obtained from two‐dimensional (2‐D) and from three‐dimensional (3‐D) trajectories. It is found that, although Sr and the energy partitioning are similar in the 2‐D and 3‐D cases, the form of σ r (Θ) and the angular momentum distribution are different. Comparison with the crossed molecular‐beam data available for this system shows that the 3‐D calculation with the potential UB yields a reasonable reaction‐energy distribution, but total and differential cross sections in disagreement with the experimental information; i.e., Sr equals 400 Å2 instead of the measured value of 7 Å2, and σ r (Θ) is independent of angle instead of being strongly peaked in the backward direction. An analysis of the scattering trajectories shows that the erroneous results derive from the neglect in the interaction potential of an attenuation factor that decreases the K, I attraction for an I atom that is part of a CH3I molecule. Introduction of such a three‐body term yields cross sections and energy distributions in qualitative agreement with the experimental data. Additional measurements are required to test the theoreticalangular momentum distribution.
41(1964); http://dx.doi.org/10.1063/1.1726060View Description Hide Description
The γ‐ray radiolysis of C3H8–C3D8 mixtures and of CD3CH2CD3 has been investigated as a function of applied electrical field up to voltages necessary to cause secondary ionization. In the saturation current region, those products which in previous studies were ascribed to ethyl and vinyl ions remain constant with a change in field strength, while products which were originally attributed to the decomposition of neutral excited propane molecules are seen to increase about fivefold before the onset of secondary ionization. The inferred yields of C2H5 + and C2H3 + per ion pair at a propane pressure of 3 cm are 0.40 and 0.08, respectively. These values compare favorably with those deduced from the fragmentation of propane within 10—10 sec as calculated by Vestal, Wahrhaftig, and Johnston on the basis of the quasiequilibrium theory of mass spectra.
The modes of decomposition of the neutral excited propane molecules formed by electron impact are the same as those observed in the vacuum‐ultraviolet photolysis at 1470 and 1237 Å. From the isotopic analysis of the products formed in the radiolysis of CD3CH2CD3 at high field strengths, it can be concluded that the average energy imparted to the neutral propane molecule by electron impact is larger than 10 eV, indicating that superexcited states of propane may be produced in the radiolysis. A value of 0.3±0.1 can be ascribed to the ratio of the number of neutral excited molecule decompositions to the number of ion pairs produced in the direct radiolysis of propane in the absence of an electrical field.
41(1964); http://dx.doi.org/10.1063/1.1726061View Description Hide Description
The reactions of O atoms with NO and NO2 have been studied using a mass spectrometer to directly measure the O‐atom partial pressure. The results obtained are as follows:
These reactions are discussed in terms of the general mechanism
The rates of the elementary reaction steps have been calculated from the over‐all rate constants and previous results on the isotopic exchange rates of 18O with O2, NO, and NO2.
41(1964); http://dx.doi.org/10.1063/1.1726062View Description Hide Description
Ultrasonic absorption measurements were made in sodium—potassium alloys at temperatures from 20° (or mp) to 150°C. The measured absorption was found to be higher than the classical absorption. In liquid sodium the bulk viscosity is attributed to structural relaxation and the ratio of bulk/shear viscosity is 3. In the alloys, in addition to structural relaxation, a second relaxation loss was observed at temperatures below 80°C. This loss was greatest for an alloy of composition near 33 at.% of K, and is attributed to the slow adjustment of the equilibrium 2Na+K⇌Na2K.
41(1964); http://dx.doi.org/10.1063/1.1726063View Description Hide Description
The thermal decomposition of nitrous oxide has been studied in the temperature region from 1500° to 2200°K. Shock‐tube techniques, employing the region behind the initial shock waves, were used. Argon, nitric oxide, and oxygen were used as diluents with 2% nitrous oxide in order that the temperature may remain practically constant during the reaction. The nitric oxide—nitrous oxide reaction appears to be bimolecular with a rate constantk 3=2.0×1014 exp[— (50 000/RT)]. The argon—nitrous oxide and oxygen—nitrous oxide reactions appear to be bimolecular at low concentrations but become unimolecular at higher concentrations. The maximum activation energy, 55 700 kcal, in the argon—nitrous oxide mixtures was obtained for the highest concentration, 1.50×10—4 mole/cc. It is shown that the decomposition occurs via the triplet states of nitrous oxide.
41(1964); http://dx.doi.org/10.1063/1.1726064View Description Hide Description
The high‐resolution emission spectra from microcrystals of three new europium benzoylacetonate chelates, EuB4HP, EuB4HM, and EuB4HD, are presented and discussed in terms of the ligand field symmetries. It is established that the ligand fields about the Eu3+ in these compounds must be of one of the point symmetries C 1, C 1h , C 2, or C 2v ; however, the exact symmetry in each case cannot be determined from the evidence presented. The emission spectra of EuB4HP and EuB4HM are found to be identical, indicating that the ligand field magnitudes and symmetries are the same for these cases. The emission spectra of EuB4HD, on the other hand, is considerably different, indicating that the magnitude and/or the symmetry of the ligand field in this compound must be different from the other chelates. A vibronic energy level for EuB4HP, probably corresponding to an europium molecular vibrational mode, was determined to be 37 cm—1 above the 5 D 0 energy level, and 33 cm—1 above the 7 F 0 energy level. A general tendency is noted in these spectra for the lines terminating on the higher ligand energy levels to be shaded toward longer wavelengths. This may be attributed to the greater number of vibronic states which are closer and more thoroughly mixed with the higher‐lying ligand field states.
41(1964); http://dx.doi.org/10.1063/1.1726065View Description Hide Description
The decay of spin polarization of optically pumped cesium atoms at room temperature in the inert buffer gases helium, neon, and argon, has been investigated at different buffer gas pressures. It has been found that the decay of the spin polarization is not a simple exponential but can be described as the sum of two exponentially decaying modes, which are interpreted as two diffusion modes. The diffusion coefficients for cesium in helium, neon, and argon are found to be 0.37, 0.24, and 0.19 cm2/sec, and the collision depolarization cross sections are 2.5×10—24, 8.4×10—24, and 26×10—24 cm2, respectively.
41(1964); http://dx.doi.org/10.1063/1.1726066View Description Hide Description
The thermodynamic functions for the isotopic exchange reaction H2O+D2O=2HDO in the gas and liquid states are computed from recent experimental data. They differ from previously published values. Excess functions for liquid mixtures of the waterisotopes are derived. For ideal solutions of the waterisotopes, these functions can be evaluated numerically. The calculated excess enthalpy of mixing is in agreement with the experimental heat of mixing. The possibility of nonideal behavior of isotopic watersolutions is discussed.