Volume 12, Issue 1, 01 January 1944
Index of content:
12(1944); http://dx.doi.org/10.1063/1.1723874View Description Hide Description
Because of the extreme complications arising from a direct deductive approach, the theory of the liquid state requires the use of a model involving simplifying assumptions. In this paper an attempt is made to formulate general principles which any such model must follow. The first step is a general discussion of ``communal'' entropy, arising from the sharing of available space by all the atoms. Arguments are advanced to support the contention that for a gas of hard elastic spheres the communal entropy is fully excited in each direction of space, and amounts in all to 3R per mole. The communal entropy of assemblages of atoms exerting normal attractive and repulsive forces (in particular, the Debye solid) is considered. The geometry, the equation of state, and the partition function for an assemblage of hard elastic spheres are considered in detail. By extension of these ideas, allowing for the type of force actually exerted on each other by real atoms, a general form of partition function for a monatomic liquid is set up. This partition function involves a sum of two parts, one corresponding to a vibrational motion expressed in terms of the Debye characteristic temperature of the solid, and the other being a translational term, each part carrying with it its own communal entropy.
12(1944); http://dx.doi.org/10.1063/1.1723873View Description Hide Description
An analysis is made of the collection and definition of a beam of ions by an ion source. It is found that the first slit of the source has no discriminating effect but the second slit does have. This is due to the fact that ions of certain values of initial energy, angle of velocity vector, and position of striking the plane of the first slit cannot get through the second one. An efficiency of collection of a source for ions of a certain initial energy is defined as the ratio of the number with that initial energy that get through the second slit to the number with that initial energy which get through the first slit. An expression for this efficiency is derived and it is applied to rather typical data to show how an abundance ratio obtained by taking the ratio of peak heights may be in error several percent. The method of measuring isotopic abundances is recommended wherein the focusing conditions are changed only by varying the magnetic analyzer field.
12(1944); http://dx.doi.org/10.1063/1.1723876View Description Hide Description
The electron affinity of oxygen atoms for one electron, the negative of the energy change at absolute zero of the reactionhas been determined to be 70.8±2.0 kcal./mole. The method used was to determine the ratio of negative ions to electrons leaving a hot filament surface exposed to oxygen gas at a low pressure.
The Resonance Emission of Cadmium Hydride Bands in Cadmium Photosensitized Reactions of Hydrocarbons12(1944); http://dx.doi.org/10.1063/1.1723877View Description Hide Description
An investigation has been made of the resonance excitation of cadmium hydride bands in mixtures of ethylene or propane with cadmium vapor illuminated with λλ3261 and 2288. With λ3261 no resonance excitation with ethylene could be detected. With propane, CdH bands were emitted with fair intensity, thus proving that the primary process in the cadmium photosensitized reactions of the paraffins isWith λ2288 no resonance emission could be detected, but the results were inconclusive.
An Application of Probability Considerations to the Mechanism of the Photochemical Polymerization of Acetylene12(1944); http://dx.doi.org/10.1063/1.1723878View Description Hide Description
The series of experiments described in a recent paper led to an account of the mechanism of the photochemicalpolymerization of acetylene based upon the hypothesis that this process should be a chain reaction operating by cycles, each of them consisting of three stages, and that chain termination ought to depend upon the probability of formation of an aromatic nucleus among the polymers resulting from each particular cycle. While nothing is known of the intrinsic probabilities of the reactions postulated, the proposed mechanism seemed to offer an opportunity for quantitative treatment by the application of probability considerations. The present paper shows that if the probabilities of the formation of products of the addition and breaking of the easily dissociated single C–C bonds in the unstable products, in the respective stages of reaction, are assumed equal, quantum yields and heats of reaction may be calculated, which are in fair agreement with data found experimentally.