Deuteron Magnetic Resonance Study of Potassium Oxalate Monodeuterate

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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%.