Herzberg-Teller

Hizhnyakov V and Tehver I 1988 Transform method in resonance Raman scattering with quadratic Franck-Condon and Herzberg-Teller interactions J. Raman Spectrosc. 19 383-8... 

Figure 6-6a. b- anil c-polarizcd absorption speclra of single crystal at 4.2 K. O and O" arc two Herzberg-Teller false origins as discussed in the text (Section 6.4.1). The most intense vibrational modes are indicated. 

We assign the peaks al 18486 cm 1 (O ) and 18657 cm 1 (O") of Figure 6-6a to vibronic levels acting as false origins which are generated by Herzberg-Teller... 

In the present simulation we apply a simple model consisting of two vibrational modes in the relevant system. The first one will contribute to the Stokes shift as well as to the Herzberg-Teller correction, while the second one only to the Stokes shift. Next, we will assume a mutual coupling of the modes in the bilinear form Q Qi for the excited state. This type of coupling is usually omitted in literature. The Hamiltonian 77s is written as... 

In the Herzberg-Teller method [22] for accounting for induced vibronic intensities, the transition moment M°e between the ground e" and excited e electronic states is expanded as a Taylor s series in the normal coordinate Q for anitsymmetric mode k... 

Figure 2.11 combines the Herzberg-Teller coupling scheme of Figure 2.9 with the level patterns and symmetries expected for the double minimum potential of Figure 2.10 and presents an overall view of the inversion levels, their vibronic symmetries, and the rotational band types. For the lower So state, the equispaced V4" manifold of levels (0o, 4i, 42,. ..) bear the vibronic symmetries A], Bi, A],. .. whereas the corresponding levels in the Si state (0°, 41, 42,. ..) are A2, B2, A2,. The transitions between the ground state zero point level, 00,... 

The 10a,1 band, as well as many bands built on it, and also the 10a , band obtain their intensity by the Herzberg-Teller vibronic coupling mechanism discussed in Section 7.3.4.2(b). 

The expressions on the right sides of Eq. (6.1-5) now involve only vibrational wavefunc-tions (vi, Vf, Ve) whereas the electronic wave functions appear in M, which is the pure electronic transition moment connecting the ground with the excited electronic state e. M is a function of nuclear coordinate and can be expanded into a Taylor series about the equilibrium position (Herzberg-Teller expansion) ... 

The vibronic theory of the RR effect distinguishes two major intensity enhancement mechanisms that play a dominant role in the RR spectra (i) Franck-Condon (FC) principle and (ii) Herzberg-Teller (FIT) vibronic coupling, which have quite different properties. The FC scattering mechanism involves displacement of the potential minima of the ground and excited electronic states along a vibrational normal... 

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