Progression of bands

Other than some solution chemistry very Uttle indeed is known about CBr2 and CI2 or about mixed dihalocarbenes. Tyerman 5 6- has observed the band spectrum of CFC1 between 3736—3466 A. Its main feature is a progression of bands with an average spacing of 386 cm 1. He also observed that, in contrast with CF2, CFC1 reacts with 02 at room temperature. 

Fig. 3. Progression of bands in the spectrum of CH20. Successive bands are separated by one quantum of the CO stretching frequency, y2, the 1A2 (excited) state. The vertical coordinate shows the relative intensity observed under low dispersion. The electronic origin (not shown) is 125 cm-1 to the red of the first member of the progression.

The UV spectrum of matrix-isolated cyclic-S20 contained a progression of bands with intervals of about 580 cm"1. This agrees with earlier IR data, which showed vasSO at 574.9 cm-1.640 The radical C1SO was detected by FTIR spectroscopy, with (vS=0) centred at 1162.9 cm-1.641... 

The spectrum of chlorine dioxide (0C10) is characterized by a well developed progression of bands covering parts of the ultraviolet and visible regions (280 to 480 nm). Cross sections were measured by Wahner et al.(1987) and by Hubinger and Nee (4994). The lifetime of OCIO against photolysis is only a few seconds. 

The continuous appearance of the B—X absorption spectrum indicates that H2O molecules in their B state also dissociate rapidly, on a timescale shorter than that of a vibrational period. The diffuse progression of banded features has been ascribed to a small fraction of the dissociating molecules being trapped for about one vibrational period prior to O—H bond fission... 

As to the determination of molecular constants, the spacings of rotational lines in the infra-red, visible, or ultra violet give information about the moments of inertia. This is frequently precise enough to serve for the unequivocal identification of the species responsible for the absorption or emission. The progression of bands in the visible yields, when enough terms are determinable to allow a satisfactory extrapolation, a value for the dissociation energy. The vibration-rotation bands of the short infra-red yield direct information about the frequencies of molecular vibration. Long infra-red and short radio waves provide values for rotations and yield moments of inertia. 

Progression of bands in solid state spectra, probably due to wagging and/or bending mode of vibration of the C—H bonds of methylene groups. The number of bands in the progression is indicative of chain length. 

Based on the fact, that doping-induced bands come from collective phonons in the doped Id-lattice, phonon dispersion curves have been calculated for different values of I [39]. For long, but finite, doped chains, k K) phonons become the so-called "translational modes", k phonons may form a progression of bands, with rapidly decreasing infrared intensity, just like the case of long, but finite, n-alkanes. These modes are generally called in the literature "shape modes". 

It should be mentioned that in the expanded region of 1150-1350 cm (Fig. 9), there is a progression of bands, corresponding to the CH2 wagging and indicative of all-trans arrangement of straight hydrocarbon chain (90). This is consistent with the models in Figure 4 proposed from the XRD data. 

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