Molecular hydrogen in nematic liquid crystals. Unusual isotope effects

Phenotypic Plasticity of Capitulum Morphogenesis in Microseris pygmaea (Asteraceae: Lactuceae)

“…It isassumed that the interaction of an external efg Fzz with the molecular quadrupole moment of the hydrogen molecule is solely responsible for the orientation of the solute. The range of sample values for the efg Fzz includes the available estimates of the external efg present in various nematic liquid crystal solvents from NMR experiments employing molecular deuterium as a probe molecule [1][2][3][4][5]28]. A number of observations that have been made before in these studies--using a gas-phase molecule model with additional simplifying assumptions about the internal and rotational motions--are confirmed by the much more advanced calculations presented here.…”

“…If in a similar vein it is assumed that the averaging over intramolecular and reorientational motions can be carried out separately in equation (14) This value is about 0.5% lower than the previous value of -24"59 [3][4][5]. This difference is essentially due to the fact that we obtain consistently lower…”

“…For molecular deuterium a value of -24.59 for BID at 298 K has been used previously as an indication for the absence of an external efg in a nematic solvent [3][4][5]. If in a similar vein it is assumed that the averaging over intramolecular and reorientational motions can be carried out separately in equation (14) This value is about 0.5% lower than the previous value of -24"59 [3][4][5].…”

“…Such studies have brought to light that in nematic liquid crystals the presence of a non-zero average electric field gradient (efg) is important [1][2][3][4][5]. The interaction between these efg's and the solute molecular quadrupole moments provides the predominant contribution to the degree of orientation of hydrogens and its isotopomers and is far from negligible in the case of other solutes.…”

Monte Carlo simulations of zero electric field gradient liquid crystal mixtures

“…Estimates of the average electric ®eld gradient, F ZZ , experienced by D 2 [2,3] have been determined from deuterium NMR. Experiments on larger methyl-and chloro-substituted benzenes indicate that these larger solutes experience an F ZZ of the same sign but reduced magnitude compared to that observed for D 2 [4±6].…”