NMR 1 J(HD) coupling in HD as a function of interatomic distance in the presence of an external magnetic field

Abstract

A theoretical study has been made of the dependence of the 1 J(HD) coupling in HD on the interatomic distance R in the presence of a static uniform magnetic field B 0. The behaviour of all coupling terms arising from Ramsey's magnetic electron-nucleus interactions, Fermicontact (FC), spin-dipolar (SD) and paramagnetic (PSO) and diamagnetic (DSO) spin-orbital interactions is analysed qualitatively for large R. It is concluded that the PSO, DSO and SD terms become negligibly small as R increases. Detailed calculations were carried out for the FC term following two different approaches: detailed full CI calculations within a non-perturbative approach; and explicit diagonalization of the Hamiltonian operator restricted to the subspace spanned by the 1Σ+;g and the 3Σ+;u states. Within the approximations considered, the FC term of 1 J(HD) is found to be independent of B 0 and to increase by several orders of magnitude, in agreement with previous results by Bacskay, G. B., 1995, Chem. Phys. Lett., 242, 507, until a critical distance R(B 0) is reached, beyond which it almost vanishes. The quenching of the coupling at R(B 0) is due to the splitting of the 3Σ+;u state in the presence of the field B 0. The stronger the field the shorter is R(B 0).