Volume 9, Issue 11, 01 November 1941
Index of content:
9(1941); http://dx.doi.org/10.1063/1.1750841View Description Hide Description
The wave numbers of 112 absorption bands of pyrimidine vapor in the 2700–3300A region have been determined. The bands have been classified qualitatively into four categories as to their intensity. Assignments of individual bands into a number of series have been made and all prominent series were found to have spacings of approximately 1014 cm—1. Other characteristic frequencies are 613, 669 and 680 cm—1.
9(1941); http://dx.doi.org/10.1063/1.1750842View Description Hide Description
The infra‐red spectrum of diborane has been studied on a prism spectrometer from 400 to 4000 cm—1. Absorption occurs over much of the region investigated. A reliable and complete analysis of the infra‐red and Raman spectra of diborane must await further work, but two alternative tentative analyses of the main features are presented which are in accord with the heat capacity of gaseous diborane from 100 to 300°K. One of these analyses is based on the assumed existence of a singlet electronic state at 412 cm—1 above the ground state and requires the potential barrier to internal rotation within the molecule to be of the order of 15,000 calories per mole. The alternative analysis assumes that no electronic state lies less than 1600 cm—1 above the ground state and requires a potential barrier of about 5000 calories per mole. Both analyses assume an ethane‐like structure for the diborane molecule.
9(1941); http://dx.doi.org/10.1063/1.1750843View Description Hide Description
In order to test the mercury vapor content of the air in a laboratory, the absorptionspectrum of this vapor is compared with a set of calibrationspectra. With a simple apparatus (``medium size'' quartz one‐prism spectrograph) vapor pressures far below the toxic limit can be determined.
9(1941); http://dx.doi.org/10.1063/1.1750844View Description Hide Description
The Gibbs adsorption relation between surface tension and concentration is applied to new data on the equilibrium pressure of spreading of oil drops containing long‐chain alcohols. It is found that the graph of pressure against concentration is an hyperbola and an empirical formula is fitted to the measurements for each alcohol. There is derived an equation of state of the polar molecules adsorbed at the oil‐water interface. It is then shown that the interfacial monolayer is a stable mixed film made up of polar and non‐polar molecules, the latter being components originally of the oil. It is pointed out that these conclusions may be significant in the interpretation of film phenomena such as are involved in the stabilization of emulsions and the structure of cell membranes.
9(1941); http://dx.doi.org/10.1063/1.1750846View Description Hide Description
Assuming that the ions in solution near a charged wall are subjected only to electrostatic and kinetic forces, it is shown that the potential gradient normal to the wall is determined principally by the valence and concentration of the ion of opposite charge to the wall. Assuming that the valence and concentration of this ion determine the effect of the salt on the electrokinetic potential of the wall, the surface potential of the wall and the thickness of the immobilized liquid layer are calculated from electrokinetic potential data. Salts of ``normal'' ions (NaCl, BaCl2, etc.) cause relatively small changes in the surface potential and thickness of the immobilized layer at a glass surface and these changes occur only at very low salt concentrations. Salts containing ``abnormal'' ions (H+, OH—, La+++, etc.) produce larger changes and the change continues over a much wider concentration range. The extreme effectiveness of salts like AlCl3 and ThCl4 in lowering negative electrokinetic potentials cannot be accounted for by the higher valence of the ions.
9(1941); http://dx.doi.org/10.1063/1.1750847View Description Hide Description
A previously developed method of calculating the thermodynamic functions of a mixture is further examined. For a lattice which is large in at least two dimensions it is shown that the largest eigenvalue of the fundamental matrix is doubly degenerate over a finite temperature range, and within this range a separation into phases takes place. An approximation to the phase boundary which is valid at low temperatures is obtained.
The Partition Functions of Molecules with Internal Torsion I. Single Asymmetric Top Attached to Rigid Framework9(1941); http://dx.doi.org/10.1063/1.1750848View Description Hide Description
Crawford's method of treating ``pseudo‐rigid'' molecules is extended to the case involving an asymmetric top. The exact classical kinetic energy for a molecule consisting of a rigid framework to which asymmetric tops are attached is given. From this the quantum‐mechanical operator is derived for the case of one top of small moment of inertia and of small asymmetry. The energy matrix for the molecule is obtained from the operator; and by use of a perturbation method, the partition function for translation, over‐all rotation and internal rotation, correct to the second order, is obtained from the matrix. This includes effects due to translational and angular momentum couplings.
9(1941); http://dx.doi.org/10.1063/1.1750849View Description Hide Description
The absorptionspectrum of C6H5Cl at 2750–2400A has been studied in the first order of a 3 m gratingspectrograph. The band system corresponds to an electronic transitionA 1→B 1 (monochlorobenzene has the symmetry C 2v ) with the transition moment lying in the molecular plane perpendicular to the C–Cl bond. In agreement with this assignment to an allowed transition the 0,0 band appears strongly. Several progressions have been found involving various totally symmetrical vibrations. Besides this ``allowed'' part of the spectrum there appear ``forbidden'' bands which are due to the excitation of a non‐totally symmetrical vibration of suitable symmetry. This vibration corresponds to the one (ε g + 606 cm—1) whose excitation is responsible for the appearance of the benzene spectrum. The analysis is supported by comparison with the absorption of solid monochlorobenzene at —259°C.