Louis R. Maxwell

Electron Diffraction by Gases

The method of electron diffraction is used for determining the C–O–C valence angle (α) in 4,4′ diiododiphenyl ether [(C6H4I)2O] and the molecular structures of phosphorus (P4) and arsenic (As4). The electron diffraction photographs were analyzed by four different methods as follows: (1) Visual measurements, (2) measurements of densitometer records, (3) conversion of densitometer records into relative intensity curves, (4) comparison of transformed intensity curves obtained by multiplying the intensity of scattering by [(1/λ) sin θ/2]2 which produces prominent maxima for measurement. The valence angle α was found to be 118±3° for 4,4′ diiododiphenyl ether, definitely greater than the oxygen valence angle found for simpler types of molecules. Phosphorus and arsenic molecules were found to have a regular tetrahedral structure within the limits of experimental error, the atomic separations being 2.21A and 2.44A, respectively, [methods (1) and (2) were used for the case of arsenic]. The minimum atomic distance...

The Molecular Structure of P4O6, P4O8, P4O10 and As4O6 by Electron Diffraction

Molecular structures of P4O6 and As4O6 were determined from electron diffraction data. P4O6 was found to have the symmetry of the point group Td with an angle P–O–P of 128.5±1.5°, and a P–O distance of 1.67±0.03A. In this structure the phosphorus oxygen distances and the phosphorus valence angles were preserved with resulting deformation of the oxygen valence angle. The separation of the arsenic atoms in As4O6 was found to be 3.20±0.05A. Because of the predominant scattering of the arsenic atoms it was difficult to determine the oxygen valence angle, As–O–As. Values of 120°, 127.5° and 140° gave approximate agreement between the observed and calculated positions of maxima. Electron diffraction photographs obtained from P4O10 differ considerably from those found for P4O6. It was not possible to explain all of the features of the P4O10 diffraction pattern by a model having the symmetry of the point group Td and it is thought that the structure might be one of lower symmetry. Data were obtained on P4O8 which...

X‐Ray and Electron Diffraction of Iodine and the Diiodobenzenes

The crystal structures of 1,3 and 1,4 diiodobenzene were determined from the x‐ray diffraction patterns of single crystals. The separations of the iodine atoms in the molecules were found to be 6.85 and 5.92A, respectively. These values are in agreement with results obtained by analysis of the electron diffraction patterns given by the vapors of these compounds. The most satisfactory explanation of the electron diffraction results for 1,2 diiodobenzene requires the I–C valence directions to be bent by about 10° from symmetrical positions in the plane of the benzene ring. In this molecule the I–I distance was found to be 4.00A, which is approximately the same as the minimum intermolecular iodine distances in crystals of the other isomeric diiodobenzenes. Electron diffraction was obtained from vapors of carbon tetrachloride and iodine. The separation of the iodine atoms in the latter molecule was found to be 2.64A; a value in agreement with band spectra data and with previous crystal structure analysis.

Molecular Structure of Nitrogen Dioxide and Nitric Acid by Electron Diffraction

New electron diffraction photographs have been taken of NO2 extending the region previously investigated to include larger angles of scattering. An interference ring was found at (1/λ) sin ½θ = 0.49 followed by another ring appearing at 0.94 as determined by visual measurements. The outer portion of the pattern consists of two rather broad rings and two well‐defined minima. Theoretical intensities of scattering were computed for various nitrogen valence angles, assuming the positions of the two oxygens to be equivalent. The best fit, and probably the correct structure, gives the angle O–N–O = 130±2° with the N–O distance 1.21±.02A. Photographs were obtained from pure nitric acid vapor at 70°—85°C. The interference maxima were measured visually as far out as the eighth maximum at (1/λ) sin ½θ = 1.83; a prominent minimum was seen at 1.54. Theoretical intensities were computed for various likely models, disregarding the scattering by the hydrogen atom. Good agreement was obtained for a planar model having an...

Electron Diffraction by the Oxides of Nitrogen

Electron diffraction has been obtained by the transmission of electrons (20–35 kv) through molecular beams of N2O, NO2, N2O4 and N2O5. The molecular structure determinations were made by using the complete electron scattering formula including the incoherent scattering. The results can be summarized as follows: (1) Nitrous oxide; for a linear model the separation of the end atoms was found to be 2.38±0.05A in exact agreement with Wierls measurement on this structure. Unfortunately it is impracticable to distinguish between models of the form N – O – N and N – N – O. (2) Nitrogen dioxide; no diffraction rings were observed which is to be expected if the molecule is triangular with the N – O distance 1.15 to 1.3A. (3) Nitrogen tetroxide; the presence of one diffraction ring at (1/λ) sin θ/2 = 0.455±0.01 lead to the conclusion that the N – N distance is 1.6 to 1.7A for the model O2N – NO2. No definite angular relationship between the two planes containing the NO2 groups could be determined. (4) Nitrogen pen...

The Crystal Structure of Polonium by Electron Diffraction

Electron diffraction photographs (λ=0.062A) were obtained from about 10—7 g of polonium that had been volatilized in a stream of hydrogen and condensed over an area of about 3 mm2 on a thin collodion film. Diffraction patterns were also obtained from bismuth and tellurium since it was expected that polonium would have a similar crystal structure. Analysis of these patterns shows that the structure of polonium closely resembles that of tellurium, the lattice being pseudohexagonal with a=4.25A, c=7.06A, or 14.12A, and the calculated density 9.39 assuming 3 Po in the pseudo unit of structure. The true lattice is probably monoclinic with a=7.42A, b=4.29A, c=14.10A and β quite close to 90°, a suggested value being β=92°; the calculated density for 12 Po in the unit of structure is 9.24. A structure, based upon the space group C23–C2, in which each polonium atom has four nearest neighbors gives moderate agreement between observed and calculated intensities of reflection.

An Electrical Method for Compounding Sine Functions

An electrical device is described for evaluating the series ΣAi sin aix. For each term in the series there is constructed one compounding element composed of three coils; a long solenoid acting as a primary (60‐cycle a.c.) within which are mounted two short secondary coils, one a rotor (order of 1/5 r.p.m.) and the other a stator. The mutual inductance between the primary and rotor varies as the sine of the angle aix of rotation while the primary current is held proportional to Ai. The vector sum of the peak voltages induced in the rotor and stator varies about a constant value proportional to Ai sin aix. Thus the variations of the resultant voltage from all of the elements about a constant value are proportional to the sum of the series. A record of the sum is made on photographic paper by means of a vacuum tube voltmeter circuit. Satisfactory tests have been made on a machine containing two elements. The application to structure determinations of gas molecules by electron diffraction is presented.