Temperature-Dependent Chemical Shifts in the NMR Spectra of Gases

Abstract

It is found that the chemical shifts of various gaseous compounds, using gaseous methane as a standard, vary with temperature. The slopes of chemical shift versus temperature at 50°C are tabulated for several compounds. This effect is ascribed to excitation of vibrational modes of the molecules, the protons in the excited molecules being differently shielded than the protons in the ground vibrational states. The data are interpreted to yield approximate chemical shifts associated with the excitation of various types of modes. NMR isotopic shifts are discussed on the basis of these data.