Signs of deuteron quadrupole coupling constants from COSY-2D spectra of solids

Abstract

It is shown how the signs of the quadrupole coupling constants (QCCs) of deuterons can be determined from the multiplet structures of the cross peaks in COSY-2D spectra of deuterons in molecular crystals or any other ordered sample. Multiplets arise as a result of dipolar couplings between pairs of deuterons. The 21) multiplet of a cross peak of a dipolar-coupled pair of deuterons consists of a 3 × 3 array of component lines. If the mixing pulse of the COSY sequence is a 90° pulse the multiplet is insensitive to the signs of the deuteron QCCs. If, however, the mixing pulse is a 54°44′ pulse only four of the nine components are strong. These are located in one of the four corners of the 3 × 3 array. In which comer of the 3 × 3 array the four strong peaks appear depends on the relative signs of the dipolar and quadrupolar splittings D, Δω Q1 and Δω Q2. This can be used as a fingerprint for the relative signs of D, D, Δω Q1 and Δω Q2. The experimental conditions of the procedure are explored in an experiment on a single crystal of fully deuterated potassium oxalate monohydrate.