Conference on the Physics of the Condensed State

Abstract

In the light of new absolute measurements of triple-differential cross sections for electron-impact ionization of helium we re-examine the various forms of the Coulomb T -matrix in the plane-wave impulse approximation. At higher energies the regularized form is supported by the measurements of Pochat et al while the Ford form is supported by the older, conflicting, measurements of van Wingerden et al. A revised calculation of the second-order Faddeev-Watson approximation is presented and compared with the measurements of Pochat et al.

Effect of the lattice vibrations on the rotational excitations in solid hydrogen

“…Since in solid H, the average longitudinal sound velocity is twice the average transverse sound velocity (Bezuglyi and Minyafaev 1967), the effect of the phonons is to flatten the pair distribution function in the direction perpendicular to the equilibrium separation of the molecules. The short-range correlations, on the other hand, force the pair distribution function to become non-centrosymmetric, since these correlations are important only when the molecules approach one another very closely and the [6.11] A2E, = -1.0 x ~O-,E, repulsive overlap forces are dominant.…”

“…These velocity measurements have been carried out on polycrystalline samples (Bezuglyi and Minyafaev 1967), giving vi(O OK) = 2200 m/s and u,(O OK) = 1160 m/s. Preliminary calculations of the phonon dispersion curves using the time-dependent Hartree approximation (Mertens and Biem 1969) are in agreement with these measurements.…”