Temperature-dependent chemical shifts and isotope shifts in the N.M.R. spectroscopy of hydrogen

Abstract

Theoretical values of the nuclear magnetic shielding constant σvJ for each of the molecules H2, HD, HT, D2, DT and T2 in their lower vibrational and rotational levels have been obtained from the results of the preceding paper. Values of the shielding constants of these compounds at temperatures in the range 0–700 K are predicted. Over the range -100 K to +200 K the shielding constant of H2 gas (at low densities) falls by 0·038 p.p.m., an amount that should be measurable. For H2, D2 and T2 there is a significant difference between the shielding constants of the ortho and para modifications at low temperatures. However, only for D2 is it possible for the N.M.R. method, in principle, to obtain a doublet splitting. For hydrogen gas the shielding constant at 300 K is calculated to be 26·297 p.p.m. This is in satisfactory agreement with the experimental value of 26·51 (±0·33) p.p.m. The isotope shift σ(HD)-σ(H2) is calculated to be 0·042 p.p.m. at 300 K. This agrees well with the three independent experimental values of 0·036, 0·038 and 0·040 p.p.m.