On the density dependence of the rotational dynamics of carbon dioxide and its 17O quadrupole coupling constant

Abstract

¹⁷ O quadrupole relaxation rates 1/T₁ of carbon dioxide are measured as a function of the fluid density at T=25 and 46°C. In order to derive both the correlation time τ₂ for the reorientational motion of the CO₂ molecule and its dependence on the fluid density, we combine these experimental data with ab initio calculations of the nuclear quadrupole coupling constant C_QF and its density dependence. These calculations show that the coupling is constant over the range of the experimental phase points and that the asymmetry parameter can be neglected. The resulting correlation times τ₂ are compared with those calculated from viscosity data via the Einstein–Debye equation and with those obtained from the extended diffusion (J-diffusion) model. The models give in limited density ranges only a qualitative description of the experimentally found behaviour.