Rotation bands, notations

In this section we first introduce the quanmm numbers, notations and conventions usually associated with the description of rotational bands. Then we look at transitions within rotational bands and classify rotational bands according to their K quantum number. We then mm our attention to the influence the... 

As in the infrared spectrum, overtone bands with Ac > 1 are possible, but have much weaker intensity and are usually not observed.) The A/= -2, 0, and +2 branches of a vibration-rotation Raman band are called O, Q, and S branches, respectively, in an extension of the P, Q, R notation used in infrared spectra. 

The so-called coordinate, or international, notation refers to the mutual orientation of the coordinate axes and symmetry elements [11], The notation always starts with the letterp, referring to the translation group. Axis a is directed along the band, axis b lies in the plane of the drawing, and axis c is perpendicular to this plane. The first, second, and third positions of the symbol after the letter p indicate the mutual orientation of the symmetry elements with respect to the coordinate axes. If no rotation axis or normal of a symmetry plane coincides with a coordinate axis, the number 1 is placed in the corresponding position in the symbol. The coincidence of a rotation axis,... 

Figure 4.1 illustrates some of the El selection rules on rotational and vibrational structure in electronic band spectra. The observed rotational selection rule, AJ = +1 (the laser-excited level with J = 50 fluorescences only to lower levels with J" = 49 or 51) is reminiscent of that in vibration-rotation spectra of molecules with no component of electronic angular momentum along the molecular axis (Chapter 3). The R- and P-branch notations in Fig. 4.1 are identical in meaning to those used in vibration-rotation spectra. In marked contrast, there is no apparent selection rule on Av = v — v" lines terminating in... 

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