Herzberg-Teller vibronic

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 transition A - X is electronically forbidden and the absorption spectrum is based on a Herzberg-Teller vibronic false origin, (Too + V5O = 2.963 eV precise value of V5 is not known. 

The radiative rate constants are governed by Herzberg-Teller vibronic mixing. The transition is principally induced by Au = 1... 

Bacon, A.R. and Hollas, J.M. (1985) Duschinsky effect caused by Herzberg-Teller vibronic coupling of two b2 vibrations in the Si-So systems of benzonitrile and phenylacetylene. Chem. Phys. Lett., 120, 477. 

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 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 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... 

The vibrational satellite structures that occur in the emission and excitation spectra (e.g.see Figs. 13 to 15) result from different vibrational activities, namely from vibronic or Herzberg-Teller activity, as introduced in this section, and from Franck-Condon activity, as discussed in the next section. 

Fig. 17. Vibronic coupling mechanisms (Herzberg-Teller couplings). The purely electronic transition between the excited state I (triplet substate) and the ground state 0 (Sq) is spin and symmetry forbidden, i.e. no intensity is found at the electronic origin I. Two mechanism are proposed. Coupling route (a) is probably more important for vibrations of metal-ligand character, while mechanism (b) preferentially induces satellite intensities by internal ligand vibrations. The electronic state S is a singlet, for which an electronic transition is dipole forbidden to the electronic ground state Sq. On the other hand, the state S , represents a singlet that carries sufficient transition probability. For detailed explanations see the text...

The delayed emission spectrum is very similar to the time-integrated emission spectrum measured at T = 1.3 K. (Compare the Figs. 22b to 13.) Therefore, this delayed spectrum is similarly assignable as described in Sects. 4.2.1 and 4.2.4. In particular, all vibrational satellites that are marked in Fig. 22 b represent false origins. Their intensities are vibronically (Herzberg-Teller) induced. Also this delayed emission spectrum does not reveal any intensity at the position of the electronic origin I. °... 

Fig. 25. Emission spectra (time-integrated) of (a) Pt(2-thpy-hg)2 and (b) Pt(2-thpy-dg)2 dissolved in n-octane (Shpol skii matrix) at a concentration of 10 mol/1. Ag c = 457.9 nm. The wavenumber scale gives the separation from the respective electronic origin I (set to zero). For both compounds, origin I does not carry any emission intensity. All vibrational satellites that correspond to fundamentals are false origins, i. e. they are vibronically (Herzberg-Teller) induced. Several vibrational modes of the perprotonated compound are correlated to those of the perdeuterated one, they are connected by dotted lines. The spectrum (a) corresponds to the one reproduced in Fig. 13. (Compare Ref. [23])...

Fig. 29. Energy level diagram for Pt(2-thpy)2 dissolved in n-octane. The electronic origin line I (0-0 transition) is not observed at zero magnetic field. The corresponding triplet substate I is radiatively deactivated via vibronic (HT = Herzberg-Teller) mechanisms. (Compare Fig. 13.) The emission lifetime given refers to T=1.3 K. The emissions from the triplet substates II and III are intense at the electronic origins and show vibrational Franck-Condon (FC) satellites. (Compare Fig. 14.) The lifetime of the Sj state of 50 fs is determined from the homogeneous linewidth of the Sq Si electronic transition at T = 1.3 K. (Compare Fig. 28)...

In centrosymmetric molecules, HRS gains intensity via Herzberg-Teller term (the first vibronic B-term), indicating that IR-active modes and silent modes are enhanced. In the case of non-centrosymmetric molecules, however, Franck-Condon mechanism (A-term) dominantly contributes to the enhancement. Moreover, the mutual exclusive rules between HRS and RS are broken, and hence, some of RS-active modes selectively appear in the spectra. In the case of plasmonic enhancement, the spectral appearance is more sensitive to molecular orientations at the metal surface because of the surface selection rules [25]. 

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