The intensity of electrons scattered by a gas can be calculated with classical as well as with quantum-mechanical methods. The range of validity of the equations obtained can be found experimentally. Comparison of the calculated and empirical intensity or radial distribution curves allows the determination of the structure and amplitudes of vibration of a molecul. – For example, it has been found that the two bromine atoms in cis-1, 3-dibromocyclobutane occupy equatorial positions. The benzene rings in biphenyl derivatives are inclined at about 45° to each other. In biscyclopentadienylberyllium, the metal atom is not located midway between the two rings.