Medium Effects in NMR. VIII. Temperature and Pressure Dependence of 19F Chemical Shifts in Pure CF4, SiF4, and SF6 Gases and in Gaseous Mixtures

Abstract

Accurate ¹⁹F NMR chemical shift measurements on pure CF₄, SiF₄, and SF₆ gases and their mixtures with other gases have been obtained. These shifts are strictly linear with density like ¹H chemical shifts. In mixtures, the second virial screening coefficient has a linear dependence on concentration within experimental errors. The chemical shifts and second virial screening coefficient exhibit a nonlinear temperature dependence. It is shown that these changes in chemical shifts can be adequately described in terms of the London dispersion field and a field due to repulsion.