The dynamic properties of liquid 3He

The dynamic structure factor S(q, omega) appropriate to the interpretation of neutron scattering measurements on 3He is studied within two theories that together cover the range of wavevectors down to the Fermi wavevector kF. Both theories express the dynamics in terms of the isothermal susceptibility chi (q) and the longitudinal frequency omega l(q). These quantities are estimated from precise X-ray measurements and a Lennard-Jones potential. An intermediate q theory is used to investigate omega q in the vicinity of the main peak in the static structure factor. omega q passes through a minimum at q=1.75 AA-1 where it has a value of some 0.4 meV. The magnitude, and to a lesser extend the position, of the minimum, is shown to be a sensitive function of the particle potential. Using a Lennard-Jones potential with De Boer and Michels parameters the authors obtain a quantitive interpretation of preliminary neutron scattering data by Scherm et al. (1974). S(q, omega does not show a narrow, intense peak indicative of a collective mode for q approximately kF.