Isotope effects on the carbon-hydrogen bond orientation of methyl iodide in nematic phase

Deuterium substitution which results in no change in molecular symmetry is demonstrated to produce negligible change in the orientation parameter (Ssub(CD)) of methyl iodide dissolved in nematic phase. Previous indirect estimates of quadrupolar coupling constants (Qsub(D)), which have assumed Ssub(CD) = Ssub(CH), are high in relation to those obtained by a direct method. This discrepancy is attributed to geometric distortion caused by dissolution of the probe molecule in nematic phase and not to the inequality of orientation parameters. (author)