Motion wagging

To the extent that the segmental friction factor f is independent of M, then Eq. (2.56) predicts a first-power dependence of viscosity on the molecular weight of the polymer in agreement with experiment. A more detailed analysis of f shows that segmental motion is easier in the neighborhood of a chain end because the wagging chain end tends to open up the structure of the melt and... 

In addition to the descriptions of group vibrations as stretch and bend (or deformation) the terms rock, twist, scissors, wag, torsion, ring breathing and inversion (or umbrella) are used frequently these motions are illustrated in Figure 6.13. 

Why does an organic molecule absorb some wavelengths of IR radiation but not others All molecules have a certain amount of energy and are in constant motion. Their bonds stretch and contract, atoms wag back and forth, and other molecular vibrations occur. Following are some of the kinds of allowed vibrations ... 

H-wagging modes of the acceptor-H complexes have not been observed in the 600 to 800 cm 1 frequency range as would be ordinarily expected (Cardona, 1983 DeLeo and Fowler, 1989). For the B—H complex, calculations show that an H motion perpendicular to the trigonal axis of the BC configuration does not raise the energy of the complex greatly (Chang... 

The attribution of lines 1 and 2 in n-type GaAs Si is further substantiated by 1) the value of the ratio of the integrated absorptions A (1-H)/Aj(2-H), which is approximately equal to three (a ratio of about two is expected since lines 1-H and 2-H are attributed to doubly and singly degenerate modes respectively), and 2) the r-factor of 1.398 for line 1, explained by the small contribution of the Si atoms to the wagging motion. 

A feature, noted SiGa—SiAs, is also observed in Fig. 17a near 393 cm-1. It is ascribed to two Si atoms on adjacent sites SiGa—SiAs (Theis and Spitzer, 1984). The intensity of this LVM also decreases after deuteration (Fig. 17b). While this donor-acceptor pair should be electrically neutral, it seems, however, it can bind a D atom, resulting in the observation of a D-related line at 704 cm-1 (972 cm-1 in the H-treated sample) this line is not related to deuterium bonded to isolated SiAs as it is not observed in every sample. It is tentatively attributed to the wagging motion of an... 

Figure 4.3 Vibrational modes of a nonlinear triatomic molecule such as H20. Arrows indicate motion in the plane of the paper, + is towards and - away from the observer, (a) symmetric stretching, (b) asymmetric stretching, (c) out-of-plane wagging, (d) out-of-plane twisting, (e) in-plane scissoring, (f) in-plane rocking.

If we accept structure 1 (Scheme 3) as possible, the position of the two CH motions, the symmetrical mode above the asymmetrical mode, would not be in accord with all data of comparable structures. Moreover, the two bending motions observed at 714 and 480 cm are very unlikely due to a rocking or wagging motion of the CH2 group. Hence, structure 1 can be ruled out. 

The vibrational spectrum of LiC2H4 presents some striking similarities to that of ethylene bonded to other metals . The C—C stretching and in-phase CH2 scissoring modes were found to be very strongly IR-activated. The other symmetrical vibrations, CH2 wagging and Li—C stretching motions, were detected at about 700 and 300 cm 48,50 ... 

The NMR spectrum of polycrystalline [PtCl2(C2H4)]2 indicates the presence of a rocking motion perpendicular to the platinum(II)-alkene bond, and a wagging about the carbon-carbon double-bond axis.695 A similar type of motion is observed in the NMR spectrum of single crystals of Zeise s salt.696... 

Figure 3.36 Schematic representation of the w and cr orbitals of CCB, and the wagging motion responsible for the electronic coupling (0 is the wagging angle). The ir orbital is represented perpendicular to the ring plane the a orbital is along the C —Cl axis.

Another example of rubber analysis is the determination of vinyl-butadiene in SBR. A PA-FTIR spectrum of a high-vinyl content SBR is shown in Figure 2.10. This determination by mid-IR methods invariably involves the use of the 910 cm"1 band due to the wagging motion of the pendent vinyl group of 1,2-butadiene. 

---