Out-of-plane rotation

In order to maximize throughput it is necessary to scan several samples simultaneously within the same imaging sequence. To this end a multi-compartment tubular holder, placed within a volume coil, was used which enabled up to 14 rat heads and 5 rabbit heads in parallel to be imaged (Fig. 1). The tubular holders were custom-made and were constructed from commonly available specimen tubes which were cut to size and glued together. The closed ends of the tubes are conical in shape which aids with the positioning of the sample as an ink spot on the snout of each fetus is aligned with the tip of the cone to control out-of-plane rotation. 

The structure of this complex is shown in Fig. 9. Ab initio calculations of the three-body potential determined the relative importance of each term. They showed [78,79] that the total three-body interaction is very anisotropic with respect to the in-plane and out-of-plane rotations of HC1 within the cluster (see Fig. 10). It is instructive to have a closer look at the composition of this three-body term. 

In-plane and out-of-plane rotational dynamics of CigRB at the toluene/water interface was evaluated using time-resolved TIR fluorescence spectroscopy [27]. The known transition dipole moment for the absorption of rhodamine B(RB) at about 530 nm (So Si) is almost parallel to that for the emission at about 570 nm (Si -> So) [28]. Time-resolved in-plane fluorescence anisotropy (r[Pg.213]

A single crystal X-ray diffraction analysis has been carried out on the bromo-substituted isocorrole derivative 2.269. This analysis revealed a somewhat non-planar macrocyclic structure (Figure 2.2.2). The non-planarity in 2.269 was presumed to arise primarily as the result of NH steric interactions present within the core of the macrocycle. As a consequence of these interactions, the two pyrroles of the dipyrrylmethene-like end of the macrocycle each twist by 23° in opposite directions out of the mean macrocyclic plane. This out-of-plane rotation of two pyrrole rings is in contrast to that observed in a typical corrole structure. In this latter case, three of the pyrrole rings are nearly coplanar, and one of the pyrroles is rotated out of plane but only by 8-10°... 

Methyl substitution of the outer aromatic rings does not significantly affect the spin density distribution (Table 2), unless the substituents are in the ortho positions, where they maximize the steric repulsion with the proton bound to the carbon adjacent to the nitrogen atom.14 The decrease of the para-hydrogen hfs constant upon ortho mono-(6+ ) and ortho disubstitution (9+ )is to be attributed to out-of-plane rotation of the substituted aryl rings caused by steric hindrance. 

There have been a number of investigations involving the study of nitroolefins as useful intermediates in the synthesis of energetic materials. A characteristic of many of them is a large twist about the double bond. Interest in the structural characteristics that accompany the rotation motivates a discussion of details. As would be expected, the rotation out of the normal planar conformation is associated with spatial crowding. Rgure 14 illustrates some of the largest out-of-plane rotations that have been measured and, in one case, calculated for crowded ethylenes [25j. 

Two conformers were detected in the microwave spectrum. Confoimer 1 exists in the siX-trans configuration with Cs symmetry, conformer II at higher energy has C symmetry and results from an out-of-plane rotation of the ethyl group. 

An intuitive description of the unusual perylene anisotropy decay is shown in Figure 12.11. When perylene is excited at a wavelength with tq = -0.2. the emission moments are symmetrically distributed in the laboratory x-y plane, and the horizontal intensity is greater than the vertical intensi (ro < 0). Because the in-plane rotaticm is more rapid th wthe out-of-plane rotation, the effect at short tj mes is to rotate the emissi on dipoles (Hit of the x-y plane toward the vertical axis. This results in the transient anisotropy values above zero (Figure 12.10). At longer times, the slower oul-of-plane motions also contribute to depo larization, and the anisotropy decays to zero (Figure 12.11). 

Figure 12.11. Effects of st in iiaiie rotation and slower out-of-plane rotation on the anisotropy decay of peiylene v th tq s -0-2. Revised and iqxinted, with permission, from Ref. 13, Academic Press. Inc.

The wavelength-dependent shifts in the differential polarized phase curves can be understood in terms of the comrifautions of various rotations to the anisotropy decay. As reasoned in our discussion of Figures I2.S and 12.6, both the in-plane and out-of-plane rotations are expected to contribute when rg = 0.4. Hence, the data for 3SI- and 442-nm excitation represent a weighted average of Di and Di- For rg vaiues near -0.2, one expects the in-plane rotation to be dominant (Hguie 12.11). This effect can be seen in the data for 281-nm excitation, for which the maximum value of A (absolute value) is shifted toward higher modulation frequencies. Finally, for rg values near... 

Another procedure is to average over initial H2O states of different parity. Fig.l4 shows relative populations of A-doublet states for different initial rotational states of H2O, averaged over two initial rotational states of H2O. For J=6, for example, the contributions from the states 6oe and 610 are summed, modelling an in-plane rotation (upper panel). If the contributions from 6go and 6gi are summed an out-of-plane rotation is modelled (lower panel). The words "inplane and "out-of-plane have to be used with care, because H2O is an asymmetric rotor. Nevertheless, the essential part of the rotation will be in-plane for the upper and out-of-plane for the lower part of Fig.l4. 

For initial out-of-plane rotations the situation is different. If there is a preference at all, it is for the tt -A-doublet state The simple adiabatic argument becomes completely wrong, because it predicts always a preference of the II"-A-doublet state, independent of the motion of the nuclei. 

Figure Relative population of A-doublet states for different initial parent motion. Above "in-plane rotations with different initial total J. Below out-of-plane rotations with different initial total J. The results are obtained by averaging over two states of different parity in the parent molecule.

The selective population of A-doublet states is exclusively determined by the parent motion and the absorption step. The origin for the selectivity is conservation of the unpaired pir-lobe relative to the direction of initial nuclear rotation. In contrast to the adiabatic picture, it is not simply electronic symmetry that is conserved. The selectivity depends sensitively on the motion of the parent molecule (initial in-or out-of-plane rotations) as well as on the coupling of the electronic motion in the products. Each rotatonal state of the parent molecule leads to another A-doublet distribution. 

An out-of-plane rotation, thermally activated at 75-100 meV, with an increasing number of molecules involved, depending on temperature above 210 K the maximum ratio is 60% above 270 K. This combination of two rotational motions, one being temperature independent, has already been observed for water molecules around a small cation in lamellar silicates . 

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