Volume 8, Issue 2, 01 February 1940
Index of content:
8(1940); http://dx.doi.org/10.1063/1.1750618View Description Hide Description
The infra‐red spectrum of methylphenylacetylene between 500 and 2300 cm—1 has been measured with the aid of a prism spectrometer. The results are compared with the Raman spectrum of this compound, previously measured by the authors. The results are inconclusive as regards the assignment of the fundamental whose overtone, according to Badger's hypothesis, is responsible for the resonance splitting of the frequency near 2230 cm—1.
8(1940); http://dx.doi.org/10.1063/1.1750619View Description Hide Description
The third and fourth harmonics of the N–H stretching frequency in hydrazoic acid, at 9547.31 and 12,412.19 cm—1, respectively, have been studied photographically under high dispersion. The rotational structure has been well resolved and completely analyzed, to yield the rotational constants in the ground and excited states. The effective moments of inertia in the ground state have been combined with other information to determine the structure of the molecule; the best values of the molecular parameters are:
Normal Vibrations of Chains of Similar and Similarly Situated Dynamical Systems and the Infra‐Red Spectrum of Undecane8(1940); http://dx.doi.org/10.1063/1.1750620View Description Hide Description
Theory indicates that the normal modes of vibration of chain molecules fall into two classes; end vibrations in which the amplitude falls off exponentially from the ends towards the middle, and chain vibrations in which it varies harmonically as in a standing wave. The transition from one class to the other takes place via chain vibrations with a small number of nodes of amplitude along the chain. For a long chain we expect only those chain vibrations to show up in the infra‐red spectrum for which the phase of the electric moment is constant along the chain.
These considerations have been applied to predict the vibration spectra of the straight chain paraffins, assumed to consist of a zigzag chain of carbon atoms each carrying two hydrogen atoms in a plane perpendicular to the chain and alternately above and below it.
The infra‐red spectrum of undecane has been measured from 1 to 15μ on a prism spectrometer, the positions of 31 bands being determined. Accepted values of the interatomic distances and angles were assumed and force constants were adjusted to fit four of the fundamental frequencies to observed bands. Bands were observed near all the other fundamental frequencies predicted certainly to occur (as chain vibrations) and near one out of three that should possibly occur (as end vibrations near chain vibrations with few nodes). All but three of the observed bands could be accounted for as fundamentals, harmonics, or simple combination frequencies.
8(1940); http://dx.doi.org/10.1063/1.1750621View Description Hide Description
Displacements, estimated intensities, and depolarization factors are listed for the main lines of diethyl ether, di‐n‐propyl ether, di‐isopropyl ether, di‐n‐butyl ether, di‐isobutyl ether, di‐n‐amyl ether, and di‐isoamyl ether. All the frequencies in the 2900 cm—1 region are polarized, except the one near 2970 cm—1 which is, without exception, highly depolarized.
8(1940); http://dx.doi.org/10.1063/1.1750622View Description Hide Description
The absorption coefficient of nitrogen dioxide in the visible spectrum has been measured at pressures up to 70 mm Hg with a 40A spectrophotometer slit. Beer's law is obeyed in this region. The transmission as measured when using a tungsten source, is the same as that oftained with either a high or low pressuremercury arc, except at the 4339–4358A group of mercury lines, where the absorption coefficient was found to be 15 percent greater with the mercury source. The absorption coefficient curve obtained with either a 40A or 15A slit is essentially sinusoidal in appearance, the absorption maxima and minima generally differing by about 10 percent in intensity. The maxima are separated by 700±100 cm—1. They appear to be due, not to the ground state of the molecule, but to groups of excited levels which are uniformly separated.
8(1940); http://dx.doi.org/10.1063/1.1750623View Description Hide Description
With a view to obtaining the internuclear distances and dissociation energies of individual bonds in polyatomic molecules purely from a knowledge of force constants the consequences of assuming that the potential energy of any di‐atom may be expressed in the form V=—α/rm +β/rn have been further investigated. In addition to giving a relation between internuclear distance and force constant of the form suggested empirically by Badger, this assumption leads to a relation between force constant (ke ), internuclear distance (re ) and dissociation energy (De ) of the form De =(kere 2)/mn. It is found that such a relation does exist between those quantities for series of diatomic molecules belonging to the same row in the periodic table, provided one uses an ``effective'' internuclear distance re—dij . This was also used by Badger in his relation of force constant to internuclear distance and the values of dij obtained by the two different methods are in reasonably good agreement. The values obtained for the product mn are 4, 6.2, 6.2 and 10.8 for the respective series LiH to FH, Li2 to F2, Na2 to Cl2 and K2 to Br2. For the hydrides it would seem that —α/r+β/r 4 is the correct form with β varying along the series. It is also shown that this function leads to a relation between the shift in frequency δv and the change in bondenergy δD in the formation of a hydrogen bond.
8(1940); http://dx.doi.org/10.1063/1.1750624View Description Hide Description
The exchange reaction of bromine and radioactive hydrogen bromide in the gas phase has been found to fall just short of reaching equilibrium in two minutes. The very rapid rate of exchange would seem to be accounted for best by a chain reaction involving bromine atoms.
Spectroscopic Evidence for Hydrogen Bonds: Comparison of Proton‐Attracting Properties of Liquids. II8(1940); http://dx.doi.org/10.1063/1.1750625View Description Hide Description
Forty‐two different organic liquids are rated according to their proton‐attracting power by comparing the strength of the hydrogen bonds which they form with heavy methyl alcohol. The classes of liquids studied are: aldehydes, ketones, esters, ethers and amines. The amount of perturbation which the different solvents cause in the OD vibrational band of the CH3OD is taken as a measure of the strength of the deuterium bridges formed with the CH3OD. The study is a continuation of a previous work in which twenty‐six similar liquids were studied, and the results agree with those of the former study in showing that according to proton‐attracting power the different classes are in the order: esters<aldehydes and ketones<ethers <amines. From the study it is possible to observe the effects of unsaturation, substitution, and other structural variations on the electron donor power of the O or N atom to which the OD group forms a bond. It is shown that the strength of the deuterium bonds formed with CH3OD bears a close relation to the basicities of the solvents, to their solubilities for other proton donor solutes, and to their reactivity with other compounds. There appears to be no correlation between the dipole moments of the solvents and the strengths of the bonds formed with the CH3OD.
8(1940); http://dx.doi.org/10.1063/1.1750626View Description Hide Description
A three‐dimensional gas is pictured in contact with a liquid, forming at the interface a mobile monolayer. The density of the monolayer is maintained in equilibrium with the pressure of the gas. An equation is deduced giving as a function of temperature, the gas pressure which is just sufficient to initiate condensation in the monolayer. The only physical parameters involved in the relationship are the mass of the molecule and the heat of evaporation per molecule from the completely clustered monolayer. The fatty acids which exhibit monolayers with negligible external gas pressures, must have heats of evaporation greater than about 100×10—14 erg. Molecules as small as 20 atomic mass units and heats of evaporation less than about 75×10—14 erg should require pressures of the order of 10—2 atmosphere. An adsorption isotherm equation is found for monolayer concentrations less than the saturation value. Its form is similar but not identical with Langmuir's isotherm for immobile monolayers.
8(1940); http://dx.doi.org/10.1063/1.1750627View Description Hide Description
Equations are derived for the entropy of long chain compounds in the gaseous state at 25°C. (1) The translational entropy, computed classically, varies with chain length according to the relation St=a+b ln n. (2) The entropy of rotation of the molecule as a whole, calculated statistically, assuming either a ball‐like molecule or absolutely random kinking, is also linear with respect to ln n. (3) The entropy of internal vibrations, assumed (following Pitzer) to be an additive function of contributions associated with the various types of bonds and bond angles present, obeys the equationSiv=a+bn. (4) The entropy of internal randomness, for randomly‐kinked molecules with no rotation, with hindered rotation, or with completely free rotation, is likewise linear in n. The equation deduced for long chain paraffins, containing but one adjustable constant (connected with the degree of hindrance of the rotation about the C–C bonds) agrees quite well with values deduced from specific heat data for short chain paraffins.
8(1940); http://dx.doi.org/10.1063/1.1750628View Description Hide Description
The problem of directed valence is treated from a group theory point of view. A method is developed by which the possibility of formation of covalent bonds in any spatial arrangement from a given electron configuration can be tested. The same method also determines the possibilities of double and triple bond formation. Previous results in the field of directed valence are extended to cover all possible configurations from two to eight s, p, or d electrons, and the possibilities of double bond formation in each case. A number of examples are discussed.
8(1940); http://dx.doi.org/10.1063/1.1750629View Description Hide Description
The theory of the first paper of this series is extended to include reactions at electrode surfaces. The resulting expression for the rate of an electrodereaction includes both activation controlled and diffusion controlled reactions. The problem of the effect of stirring rate on reaction rate is discussed. The results are applied to the theory of reactions at ``floating'' electrodes, e.g. the solution of metals in acids. It is shown that the reaction rate expressions at such electrodes are of a very complex form, but can be approximated in special cases. It is found that the rate of such a reaction will in general depend not only on the concentration of the principal reactants, but also on the concentration of every ion in the solution.
8(1940); http://dx.doi.org/10.1063/1.1750630View Description Hide Description
A theory of phase changes due to hindered molecular rotation in crystals is developed on the basis of classical statistical mechanics. It is demonstrated that local hindrance of relative rotation of neighboring molecules in the lattice can produce a non‐uniform distribution in orientation below a certain critical temperature. The theory provides a semi‐quantitative description of the behavior of the hydrogen halides in certain of their lambda‐transitions, with a relative torque potential of the form (ε/2) cos γ for a pair of neighboring molecules, the axes of which are inclined at an angle γ to each other. The barrier height ε is estimated to be between 200 and 300 cal./mole for hydrogen iodide and hydrogen bromide.
8(1940); http://dx.doi.org/10.1063/1.1750631View Description Hide Description
Following upon the general theory in Part I, a considerable simplification is here introduced in the treatment of the case where the grain centers of the new phase are randomly distributed. Also, the kinetics of the main types of crystalline growth, such as result in polyhedral, plate‐like and lineal grains, are studied. A relation between the actual transformed volume V and a related extended volume V 1 ex is derived upon statistical considerations. A rough approximation to this relation is shown to lead, under the proper conditions, to the empirical formula of Austin and Rickett. The exact relation is used to reduce the entire problem to the determination of V 1 ex, in terms of which all other quantities are expressed. The approximate treatment of the beginning of transformation in the isokinetic range is shown to lead to the empirical formula of Krainer and to account quantitatively for certain relations observed in recrystallization phenomena. It is shown that the predicted shapes for isothermal transformation‐time curves correspond well with the experimental data.
8(1940); http://dx.doi.org/10.1063/1.1750632View Description Hide Description
The metallic character of the crystals of silver sub‐fluoride was studied in terms of the magnetic susceptibility. It was found that the conduction electrons contribute a considerable diamagnetism which was related especially to the anisotropy of the crystals.
8(1940); http://dx.doi.org/10.1063/1.1750633View Description Hide Description
Crystals of hydrated europium chloride possess structures in their absorptionspectrum which are faint but accurate repetitions of the intense patterns arising from electronic transitions in in the europium ions. These repetitions occur on both sides of the intense patterns at intervals which are ascribed to oscillations of the lattice, thermally as well as optically excited oscillations. The spectra of aqueous solutions of europium chloride and also of europium nitrate closely parallel the structures in the spectrum of the crystals. In the region where the crystals absorb, the solutions absorb also. The structures in the spectra of the solutions are somewhat more diffuse than the corresponding structures in the spectra of the crystals. Especially is this true for the structures at the intervals corresponding to lattice vibrations.