Infrared spectrum, negative frequencies

The four normal modes of vibrations of a pyramidal XY3 molecule are shown in Fig. 2.8. All four vibrations are both infrared- and Raman-active. The G and F matrix elements of the pyramidal XY3 molecule are given in Appendix VII. Table 2.3a lists the fundamental frequencies of XH3-type molecules. Several bands marked by an asterisk are split into two by inversion doubling. As is shown in Fig. 2.9, two configurations of the XH3 molecule are equally probable. If the potential barrier between them is small, the molecule may resonate between the two structures. As a result, each vibrational level splits into two levels (positive and negative) [560]. Transitions between levels of different signs are allowed in the infrared spectrum, whereas those between levels of the same sign are allowed in the Raman spectrum. The transition between the two levels at u = 0 is also observed in the microwave region (v = 0.79 cm ). 

Spectroscopic evidence confirms the fact that the two Meisen-heimer compounds (36), that formed from s-trinitroanisole and eth-oxide ion and that formed from s-trinitrophenetole and methoxide ion, are identical. The two products give identical infrared t45) and visible spectra (46). The infrared spectrum is characterized by a shift in the N-0 symmetrical stretching frequency from 1343 cm. in s-trinitroanisole to 1291 cm. in the product and a shift in the N-0 asymmetrical stretching frequency from 1552 to 1492 cm. b These differences can be attributed to increased negative chai on the nitro groups and are consistent with the proixtsed structure 111. 

For a reasonable set of the parameters the calculated far-infrared absorption frequency dependence presents a two-humped curve. The absorption peaks due to the librators and the rotators are situated at higher and lower frequencies with respect to each other. The absorption dependences obtained rigorously and in the above-mentioned approximations agree reasonably. An important result concerns the low-frequency (Debye) relaxation spectrum. The hat-flat model gives, unlike the protomodel, a reasonable estimation of the Debye relaxation time td. The negative result for xD obtained in the protomodel is explained as follows. The subensemble of the rotators vanishes, if u —> oo. 

Many other interaction energies come from the electromagnetic frequency spectrum. They can come from outside of the ultraviolet, visible, and infrared frequency ranges. All that is required is an element of the model protein in water that is able to take up the energy. The dipole moment of the peptide group with its positive end at the NH and its negative end at the oxygen of the CO provides one site of inter-... 

Figure 3 A far infrared scan of methanol a pressure of about 10 Pa of methanol and a frequency modulation of 2.5 MHz were used to record the spectrum. Both sidebands are shown the lines which are positive on the left are those in the increasing frequency sideband and vice versa for those which are negative on the left. The frequencies are in megahertz.

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