Deuteron Magnetic Resonance Study of Potassium Oxalate Monodeuterate

Abstract

Quadrupole splittings of the Larmor resonance for the deuteron in potassium oxalate monodeuterate (K₂C₂O₄·D₂O) were measured for single crystals at temperatures from −50° to 95°C. The D₂O molecule is stationary at room and lower temperatures. The coupling constant and asymmetry parameter were determined to be 209.7±2.5 kc/sec and 0.090±0.020, respectively. The z field‐gradient axis is within 4.8°±2.0° of parallelism with the O—D bond while the y axis is in the a—c plane and within 4.6°±2.0° of being perpendicular to the DOD plane. The D₂O molecule begins to 180° flip about its DOD bisector at 25°—50°C and higher. The coupling constant and asymmetry parameter of the flipping molecule are 114.2 kc/sec and 0.851, respectively. The z field‐gradient axis is nearly perpendicular to the DOD plane while the y axis is nearly parallel to the D—D vector in its equilibrium position. Both axes are in the a—c plane and rotated away from perpendicularity and parallelism, respectively, by 4.6°±2.0°. The coupling constants of this and three other deuterates differ among themselves and they are markedly lower than the computed and measured values for the isolated D₂O molecule. Reasons for these differences are discussed including hydrogen bond strengths and D₂O motion. For this crystal the field gradient due to nearby ions was estimated on the basis of a simple model and it was found to augment the measured coupling constant by about 9%.