Wavenumber difference

The illustration of various types of vibronic transitions in Figure 7.18 suggests that we can use the method of combination differences to obtain the separations of vibrational levels from observed transition wavenumbers. This method was introduced in Section 6.1.4.1 and was applied to obtaining rotational constants for two combining vibrational states. The method works on the simple principle that, if two transitions have an upper level in common, their wavenumber difference is a function of lower state parameters only, and vice versa if they have a lower level in common. 

Since the Raman scattering is not very efficient (only one photon in 107 gives rise to the Raman effect), a high power excitation source such as a laser is needed. Also, since we are interested in the energy (wavenumber) difference between the excitation and the Stokes lines, the excitation source should be monochromatic, which is another property of many laser systems. 

Equation (7.89) also shows that Dq may be obtained from vlimit since Avatomic is the wavenumber difference between two atomic states, the ground state 2P3/2 and the first excited state 2 P /2 of the iodine atom, known accurately from the atomic spectrum. Thus the accuracy of D, j is limited only by that of vlimit. 

Figure 6 Total flux through a dividing surfiace between donor and acceptor (a plane perpendicular to the longest axis of the molecule) as a function of the position of the surface. The horizontal axis indicates the coordinate along the longest axis of the molecule, in Bohrs, as in Fig. 4, where the surface crosses the pol3rpeptide. The vertical axis is the total flux, which by Eq. (6) is equal to transfer matrix element, measured here in wavenumbers. Different ciurved correspond to different transition states, described in the text.

Since the carbonyl group of stilbazolium betaine possesses two lone pairs in the plane of the quinoid ring, one can have two (11), one (TBSB, 13) or no channels (DTBSB) to approach hydrogen bond-donor solvents, depending on the number of o-tert-butyl groups present in the molecular structure of the (11) derivative concerned. Our group has also shown that, for at least 20 alkanols, the wavenumber difference between the maximum of the first absorption bands for (11) and TBSB, and for TBSB and DTBSB, is virtually identical. 

Second, it is well suited to gain information on molecular states if the fluorescence spectrum excited by a laser on a selected absorption transition is dispersed by a monochromator. The fluorescence spectrum emitted from a selectively populated rovibronic level (f, / ) consists of all allowed transitions to lower levels (i , 7 ) (Fig. 1.51a). The wavenumber differences of the fluorescence lines immediately yield the term differences of these terminating levels J ). 

Flg 2. Calculated ratio of reflected intensity immediately after pump pulse to its equilibrium value, as a function of wavenumber difference between the probe and pump beams (l/ i Straight line indicates... 

Over-deconvolution has another insidious effect when the spectrum is being smoothed simultaneously. When spectra are over-deconvolved, the sidelobes that appear may be smoothed to the point that they are often manifested as apparent shoulders on real bands. The effect of over-deconvolution is that many bands seem to have been resolved. One way of checking for this occurrence is to measure the wavenumber difference between successive shoulders. If this difference is constant, it is more likely than not that the shoulders are due to sidelobes and the deconvolution has been performed incorrectly. 

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