Index of content:
Volume 20, Issue 11, 01 November 1952
20(1952); http://dx.doi.org/10.1063/1.1700264View Description Hide Description
Alternate expressions for the second virial coefficient of a gas having a Lennard‐Jones 6–9 potential are derived to cover the temperature range where the known power series expansion in θ=ε/kT is inconvenient for numerical computations. For θ≥2 the second virial coefficient can be expressed as a combination of Bessel functions of imaginary argument plus a small correction term. This formulation and an asymptotic expression derived from it are used to tabulate numerical values of the second virial coefficient in the range 2≤θ≤100.
20(1952); http://dx.doi.org/10.1063/1.1700265View Description Hide Description
For low temperatures, the second virial coefficientof a gas which follows a Lennard‐Jones 6—s potential,where θ=ε/kT, can be represented byIn two previous studies, formulas for β n (9) and β n (12) have been presented. In this paper, the relation for Gs (θ) is developed for the general case, using the method of steepest descents, and the first three coefficients β0(s), β1(s), and β2(s) are computed. The use of a Hooke's law potential and the quasi‐ideal gas hypothesis yields the correct leading term in Gs (θ), but results in errors in β1(s) and β2(s).
20(1952); http://dx.doi.org/10.1063/1.1700266View Description Hide Description
The reaction of Hg(3 P 1) with ethylene at room temperature has been re‐investigated. Special attention was paid to the effects of the concentrations of ethylene and mercury on the reaction velocity. The results are in general agreement with a mechanism which requires the excited ethylene, produced initially, to decompose both in the gas phase and on the wall. The results are also compatible with the suggestion that a significant fraction of the quenching collisions between ethylene and Hg(3 P 1) leads to the formation of metastable (3 P 0) atoms.
20(1952); http://dx.doi.org/10.1063/1.1700267View Description Hide Description
The reaction of Cd(3 P 1) with propane has been investigated at 300°C under such conditions that the rates of production of hydrogen and methane are independent of time. The quantum yield of hydrogen production, when corrected for incomplete quenching, is close to unity and is approximately independent of the substrate pressure. The production of methane can be accounted for by the decomposition of propyl radicals. The ratio CH4/H2 increases with decreasing pressure of propane; if this ratio varies as I a −½ (as is the case when the methyl radicals are produced by the thermal decomposition of propyl radicals), the increase may be ascribed to the decreasing absorbed intensity at lower pressures.
20(1952); http://dx.doi.org/10.1063/1.1700268View Description Hide Description
The production of metastable (3 P 0) mercury atoms in the quenching of mercury resonance radiation has been investigated with N2, H2, C2H4, C2H6, O2, and CO2. Metastable atoms, by virtue of their ability to induce the emission of electrons from a nickel surface, were detected with the first four gases; none was detected with O2 and CO2.
20(1952); http://dx.doi.org/10.1063/1.1700269View Description Hide Description
A study has been made of recoil halogen species ejected from gaseous ethyl bromide and iodide after neutron capture. The results demonstrate that a fraction of the radio‐halide fragments carry a positive charge. The fraction charged is 12 percent for the 4.4‐hr Br80m , 25 percent for the 36‐hr Br82, and 50 percent for the 25‐min I128. The corresponding estimate for the 18‐min Br80 is very approximately 18 percent. The positive charges are attributed to internal conversion processes in the stabilization of the compound nucleus formed by neutron capture. The fraction of positive recoil ions is interpreted as the minimum fraction of neutron capture processes which are followed by an internal conversion process. A comment is made upon the possible significance of the ions in the study of chemical reactions induced by radiative neutron capture.
A study of the 18‐min Rb88 from β‐decay of the 2.8‐hr Kr88 was made using the procedures and equipment employed in the halogen experiments. The results show that all Rb88 atoms are positively charged as expected.
20(1952); http://dx.doi.org/10.1063/1.1700270View Description Hide Description
Work on the microwave spectra of CH3Cl, SiH3Cl, GeH3Cl, CH3Br, SiH3Br, and GeH3Br, performed at this laboratory and others, is summarized, and preliminary reports of work at this laboratory are expanded. Structural parameters, dipole moments, and quadrupole coupling constants obtained from analysis of these spectra are tabulated and discussed, and a unified picture of the bonding in these series of molecules, based on the derived quantities, is presented.
20(1952); http://dx.doi.org/10.1063/1.1700271View Description Hide Description
The cyclobutane molecule has been found by electron diffraction to have the following bond distances and bond angles: C–C, 1.568±0.02A; C–H, 1.098±0.04A; ∠HCH, 114±8°. On the average the ring is nonplanar, with dihedral angle 20° (+10°, −20°), but the equilibrium symmetry may be either D 2d (puckered ring) or D 4h (planar ring with low rigidity leading to large amplitude of out‐of‐plane bending). This point is discussed in connection with earlier spectroscopic work. The long bond distances found in four‐membered rings are contrasted against the short distances in three‐membered rings, and the strain energies, bond distances, and HCH angles of cycloalkanes are discussed in terms of modern valence concepts. It is suggested that the potential energy arising from a repulsion of the nonbonded carbon atoms may contribute significantly to the apparently anomalously high strain energy of cyclobutane. The repulsive force associated with such a potential is shown to account satisfactorily for the long C–C distances.
20(1952); http://dx.doi.org/10.1063/1.1700272View Description Hide Description
Cyclopropene, C3H4, has been investigated by the electron diffraction method. The cyclic structure is confirmed and the following interatomic distances and angles are found: C–C, 1.525±0.02 A; C=C, 1.286±0.04 A; 〈C–H〉, 1.087±0.04 A; ∠H–C–H, 118° (assumed); ∠C=C–H, 152±12°.
20(1952); http://dx.doi.org/10.1063/1.1700273View Description Hide Description
The absorptionspectrum of hydrogen sulfide in the region from 5000 to 5250 cm−1 has been measured and the rotational fine structure analyzed. The structure can be accounted for as arising from two vibrational transitions yielding a type A band centered at 5147 cm−1 and a type B band centered at 5145 cm−1. The excited state constants giving the best fit are type A band, A *=10.04, B *=8.68, C *=4.61 cm−1; type B band, A *=10.08, B *=8.68, C *=4.59 cm−1.
The frequencies and rotational band types indicate that these bands are the (n σ, n π, n δ)=(110) (type A) and the lower component of the resonating pair (020) (200) (type B).
20(1952); http://dx.doi.org/10.1063/1.1700274View Description Hide Description
The sorption kinetics for the system polyvinyl acetate‐acetone have been investigated both above and below 30°C, the second‐order transition temperature for the pure polymer. At 30, 40, and 50°C, the diffusion obeys Fick's law with a concentration‐dependent diffusion coefficient. With increasing acetone concentration the value of the diffusion coefficient increases strongly, and the energy of activation for diffusion decreases. At each temperature below 30°C, diffusion is Fickian only for sorption and desorption experiments where the solvent concentration is above a certain critical value. It was found, by comparison with the results of volume‐temperature measurements on the system polyvinyl acetate‐acetonyl acetone, that the temperature corresponding to a given critical concentration is the second‐order transition temperature for this polymer‐solvent mixture. Evidently, the changes which occur at the second‐order transition have a pronounced influence on the diffusion process.
20(1952); http://dx.doi.org/10.1063/1.1700275View Description Hide Description
The infrared spectra of NF3 and PF3 have been investigated with a prism instrument in the range 250 cm−1 to 5000 cm−1. The fundamental frequencies are for NF3, ν1(A 1)=1032 cm−1, ν2(A 1)=647 cm−1, ν3(E)=905 cm−1, and ν4(E)=493 cm−1; and for PF3, ν1(A 1)=892 cm−1, ν2(A 1)=487 cm−1, ν3(E)=860 cm−1, and ν4(E)=344 cm−1. Force constants as well as thermodynamic functions are calculated for both molecules.
20(1952); http://dx.doi.org/10.1063/1.1700276View Description Hide Description
The Raman spectra of chloroacetyl chloride, bromoacetyl chloride, and bromoacetyl bromide have been measured in the solid and liquid states. The infrared absorption spectra of these substances have also been measured in the liquid and the gaseous states. From the experimental results it has been concluded that there are two rotational isomers in the liquid and gaseous states and only one of them persists in the solid state. The temperature dependence of the intensity of the infrared absorption in the gaseous state has also been studied, and the energy difference between these two isomers has been found as 1.0±0.1 kcal/mol for bromoacetyl chloride and 1.9±0.3 kcal/mol for bromoacetyl bromide.
The calculation of the normal vibrations and of the product rule has been made for various configurations of rotational isomers, and it has been shown that the more stable form is the trans form (or nearly this one) with regard to the two halogen atoms. The less stable form is considered to have an azimuthal angle between the two carbon‐halogen bonds of about 150°.
Kinetics of Decomposition of Nitric Oxide at Elevated Temperatures. II. The Effect of Reaction Products and the Mechanism of Decomposition20(1952); http://dx.doi.org/10.1063/1.1700277View Description Hide Description
The effects of nitrogen and oxygen on the kinetics of decomposition of nitric oxide have been investigated. In the temperature region in which the heterogeneous mechanism prevails (at T<1000°K) the presence of nitrogen has a marked retarding influence on the reaction rate of nitric oxide due to poisoning of the surface. On the other hand, the addition of oxygen results in a marked increase in the rate of decomposition of nitric oxide over the entire temperature range studied. At high concentrations of oxygen the following empirical rate expression obtains,with an activation energy of 78.2 kcal for the rate‐determining step. It is apparent therefore that the decomposition of nitric oxide is autocatalytic. On the basis of these experimental observations a mechanism is proposed involving a chain propagated by the atomic species formed in the reaction.
20(1952); http://dx.doi.org/10.1063/1.1700278View Description Hide Description
The absorption bands of the oxygen molecule in the extreme ultraviolet region were studied using a 3‐meter grazing incidence vacuum spectrograph. Two new progressions of bands were found in the region between 1200A and 1290A (one of which is considered to be a member of the Rydberg series converging to the first ionization potential of the oxygen molecule). There were also observed a few short continua near the short wavelength end of the Schumann‐Runge absorption continuum. The behavior of three strong and diffuse bands, at 1200∼1290A, were studied at pressures ranging from 0.01 to several mm of Hg. Assuming the diffuseness of these bands as being due to predissociation, the existence of oxygen atoms in 1 S metastable states in the upper atmosphere is briefly discussed.
20(1952); http://dx.doi.org/10.1063/1.1700279View Description Hide Description
The electron‐impact‐induced dissociations of cyclopropane are determined from the appearance of potentials of the several ions formed. In general, the dissociations involve a considerable amount of atomic rearrangement, and the evidence points to the opening of the carbon ring in the formation of the C3 ions. The energy required to convert cyclopropane to ethylene and methylene is found to 77 kcal/mole, from which it is estimated that the C–C bond dissociation energy in cyclopropane is at least 50 kcal/mole. The unexpectedly good agreement of the values of the heat of formation of an ion formed by electron impact from several different sources is noted, and a question is raised as to the role of activation energies in the electron‐impact dissociations of polyatomic molecules.
20(1952); http://dx.doi.org/10.1063/1.1700280View Description Hide Description
The vapor heat capacities of ethyl alcohol have been measured, as a function of pressure, at 368, 422, and 476°K. From the variation of the heat capacity with pressure, together with vapor densities calculated by the Clapeyron equation, an equation of state for ethyl alcohol has been obtained. This equation has been used to extrapolate the measuredheat capacities to the ideal gas state and likewise to correct the observed entropy.
The infrared spectra of vapor C2H5OH, C2H5OD, and liquid C2H5OD are presented and a vibrational assignment is obtained which is sufficiently reliable for the statistical calculation of the thermodynamic properties.
Comparison of the observed and statistically calculated heat capacities and entropies shows that, with a barrier to internal rotation of the CH3 group of 3000 calories, the rotation of the OH group is hindered by a barrier between 0 and 1200 calories. Most satisfactory agreement is obtained for CH3 and OH barriers of 3300 and 800 calories, respectively. Furthermore, comparison of the observed and calculated equilibrium constants for the reactionsupports the selection of fundamental frequencies and internal rotation barriers.
20(1952); http://dx.doi.org/10.1063/1.1700281View Description Hide Description
The individual absorption coefficient curves of NO2 and N2O4, separated by means of a mechanical analog differential analyzer are presented. Beer's law is assumed to be applicable to the system. The range 2400–5000A is covered. A discussion of the apparently continuous nature of the N2O4 absorption is included.
20(1952); http://dx.doi.org/10.1063/1.1700282View Description Hide Description
The infrared spectra of solid decaborane and of decaborane in a solution of carbon disulfide as well as the Raman spectrum of the solution have been recorded. A rough selection of fundamental frequencies is made; this, together with the molecular parameters from x‐ray data, is used for calculating S 298.16 0 of the gas, for which a value of 83.85 eu is obtained. This figure compares with that derived from thermodynamic measurements, namely, 87.36 eu.
20(1952); http://dx.doi.org/10.1063/1.1700283View Description Hide Description
The semiclassical Franck‐Condon principle is shown to be related to the more rigorous (``exact'') quantum‐mechanical perturbation formula in the following ways: (1) the Franck‐Condon formula can be derived from the ``exact'' formula by using a mean value approximation or by neglecting certain commutators; (2) if the electric dipole moments are treated as approximately independent of position, the Franck‐Condon and the ``exact'' absorption (or emission) spectrum have the same zeroth, first, and second moments, i.e., the same integrated spectrum, mean absorption frequency, and breadth; (3) the errors in higher moments than the second become relatively unimportant at high temperatures. If the electron‐nuclear interaction is sufficiently strong the errors are unimportant even at absolute zero.
The use of a quasi‐molecular description in a many particle problem is found to be possible only if the masses or stiffnesses are allowed to be temperature dependent.
A detailed analysis is made of the case in which the energy difference between the two electronic states is a linear function of the vibrational coordinates—and the latter are describable by normal modes. ``Exact'' formulas for the absorption and emission spectrum are obtained.