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 distances as found by crystal structure analysis for phosphorus and arsenic are approximately the same as the atomic separations obtained for the gas molecules, showing in addition that these distances do not change greatly when the bond angle decreases from 100° to 60°.