The chemical shift of deprotonated water dimer: Ab initio path integral simulation

The H-1 NMR chemical shift in deprotonated water dimer H3O2- has been studied by ab initio path integral simulation. The simulation predicts that the isotropic shielding of hydrogen-bonded proton increases as a function of temperature by about 0.003 ppm/K. This change is about an order of magnitude larger than that of the nonhydrogen-bonded proton. It is concluded that this is caused by the significant difference in the quantum distribution of proton at high and low temperatures in the low barrier hydrogen bond.