The perpendicular orientational relaxation time (τ⊥) of the nitrate ion was determined as a function of concentration by the Raman line shape analysis (ν1 stretch) in aqueous LiNO3 and KNO3 solutions in the range of 0.2–1 M and by the nuclear magnetic resonance (NMR) T1 measurement (14N) in MNO3 (M=Li, Na, K, and Cs) solutions in the range of 0.02–1 M; the parallel orientational relaxation time (τ∥) was also determined by the NMR measurement for the solutions enriched in 17O. Both τ⊥ and τ∥ increase linearly with increasing concentration up to 1 M; the limiting values of τ⊥ and τ∥ were 1.25 and 1.9 ps, respectively. The slope increases with the surface charge density of the countercation except for Li+. These trends are predicted in very dilute solutions by the continuum theory developed in the previous paper. The anomalous behavior of Li+ was explained in terms of its strong hydration.
ouf-of-plane deformations. The calculated Ca-C,-C6-H angle is 1.41°and the Q-Ca-C^-H^angle is 0.63°. The phenyl ring of the C, internal rotational saddle point conformer is aldo distorted. The calculated Ca-C,-C2-C3 angle is 179.68°.The earlier HF/6-31G torsional potential18 was obtained under the constraint that the phenyl ring and the vinyl group maintain planarity. In order to compare our HF/6-31G* results with this HF/6-31G potential, the geometries of the twisted energy minimum and the perpendicular saddle point conformers were reoptimized under the planarity constraint using the 6-31G* basis set. The energy increments by imposing the planarity constraint for the twisted and perpendicular conformers are only 0.037 and 0.007 kcal/mol, respectively. The planarity restrictions only affect the calculated bond distances by less than 0.001 Á and valence angles by less than 0.1°. Charge Distribution. Despite the dependence of the Mulliken population analysis on the employed basis set,33 it is of interest to see the changes of charge distribution with the change of geometry. Total electron densities and Mulliken overlap populations for the planar, the twisted, and the perpendicular saddle point conformers in the 6-31G* basis set are given in Table V.The increase of the twist angle causes an increase of the electron densities on C, and Cn and a decrease of those on C6 and Cs, as for the HF/6-31G calculations.18 The calculated dipole moments for the planar, the twisted, and the perpendicular conformers are 0.163, 0.147, and 0.016 D, respectively. The calculated dipole moment for the planar conformer is close to the value of 0.159 D given by the HF/6-31G calculation. The calculated dipole moment for the twisted conformer agrees well with the experimental value of 0.12 ± 0.03 D measured in the liquid phase34 and of 0.122 ± 0.001 D in the gas phase.8
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