High resolution nuclear magnetic resonance spectroscopy in liquids and gases at pressures up to 2500 bar: II. Density dependence of the proton magnetic shielding constants in the nonpolar gases methane and ethylene

The density dependence of the proton magnetic shielding constant σ in methane and ethylene has been investigated experimentally using a high resolution spectrometer which operates with hydrostatic pressures between 0 and 2500 bar. At a constant temperature of 29.2°C a nonlinear dependence of σ on the density ? has been observed for both CH₄ and C₂H₄ in density intervals from 0–575 amagat and 0–475 amagat, respectively. Using the same apparatus the diamagnetic molar susceptibilities of the two gases have also been determined. The experimental results are discussed theoretically by comparing the observed variations of the shielding constants to the values calculated with theoretical models taken from literature.