Theory of resonance raman scattering by degenerate modes due to renner-teller interactionin porphyrins
✍ Scribed by Willem Siebrand; Marek Z. Zgierski
- Publisher
- Elsevier Science
- Year
- 1979
- Tongue
- English
- Weight
- 322 KB
- Volume
- 63
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
Resonance Raman spectra and excitation profiles associated with Renner-Teller coupIing in square molecules are ar&ysed theoretically and an experiment is proposed to warch for this effect in metalioporphyrins-One of the most successful applications of resonance Raman spectroscopy to date has been the unraveling of vibronic coupling patterns in metatloporphyrins [I -6]_ The basic Dab symmetry of these moIecuIes, sometimes weakly broken by substituents, leads to (pseudo-) Jahn-Teller coupling within the manifolds of (pseudo-) degenerate states-Two such (E-type) states are known to give rise to prominent absorption bands, nameIy 3 weak, low-energy "Q" band and a strong higher-energy "B" (or Soret) band-Since these states derive from the same pair of degenerate z-orbit&, they are susceptible to Hetzberg-TeIIer coupling, a mechanism which transfers transition moment from the B to the Q band. As a resuit the Q band shows a broad feature (~3 band) which is bmicaIIy z superposition of induced O-l bands of nontotaiIy symmetric modes_ Such Herzberg-Teileractive modes can belong to the representations al, aI, bt and b2_ The last two _representations are ako Mm -Teller active. The corresponding coupiings have been recognized and their reiative contributions to resonance firnan spectra and excitation profiles have been assessed for several porphyrins [3-51. There is, however, a third type of vibronic coupIing which rematins to be detected in these systems, namely Renner -TeiIer coupling [7,8] within each degenerate state through degenerate (e-type) modes of vibration_ This coupiing differs from Mm-Teller coupling through " Issued as XRCC Xo. f?396_ * NRCC Research &sociate_