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Advanced Spectroscopy: Computation of Magnetic Vibrational Circular Dichroism

Advanced Spectroscopy: Computation of Magnetic Vibrational Circular Dichroism. Basic idea of working with polarized light : We get m ore information t han with unpolarized one. Example : ROA. Spectra from Charles University, Prague. Chiroptical Methods. Natural Chirality.

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Advanced Spectroscopy: Computation of Magnetic Vibrational Circular Dichroism

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  1. Advanced Spectroscopy:Computation of Magnetic Vibrational Circular Dichroism

  2. Basic idea of working with polarized light:We getmore informationthan with unpolarized one Example: ROA Spectra from Charles University, Prague

  3. Chiroptical Methods Natural Chirality Induced by a Magnet

  4. MVCD Experiment

  5. MVCD Experiment RR (gas) MVCD Pure vibrational (liquid state) MVCD • Theory: • qualitative explanations • “A terms” only • cannot simulate spectra • modern approach needed X not now !

  6. Perturbation of Vibrational States in the Magnetic Field n(+),n(-) nX, nY B (mixing and splitting) but in solution: average energy zero ….

  7. Perturbation of Vibrational States in the Magnetic Field n(+),n(-) nX, nY B (mixing and splitting) How to imagine: nY nX - + but in solution: average energy zero …. -

  8. Perturbation of Vibrational States in the Magnetic Field n(+),n(-) nX, nY B (mixing and splitting) How to imagine: nY n(+) = nX + inY + nX - + but in solution: average energy zero …. m -

  9. Perturbation of Vibrational States in the Magnetic Field - Math

  10. Perturbation of Vibrational States in the Magnetic Field - Math

  11. Perturbation of Vibrational States in the Magnetic Field - Math Second-order perturbation theory:

  12. (cont.) … molecule fixed frame

  13. (cont.) … molecule fixed frame … solution: isotropic (rotational) averages, e.g. “Faraday’s B-term” of Stephens, but for vibrations

  14. … but if Ejk = 0 ? “Dirty” trick: spectral lines always broad,can introduce arbitrary perturbation replace (1/E) by f(E)/2 E < 0

  15. … but if Ejk = 0 ? “Dirty” trick: spectral lines always broad,can introduce arbitrary perturbation replace (1/E) by f(E)/2 E < 0 … no effect |E| > 0: f(E) = . E = 0: Shape does not depend on d

  16. … closer look APT derivatives Equilibrium dipole APT AAT zero AAT derivatives harmonic part ... does not contribute to B-term AAT derivatives are the leading term for MVCD

  17. MVCD working equation APT, from Gaussian directly AAT derivatives, from Gaussian numerically vibrational (harmonic) frequencies, from Gaussian directly

  18. 1,3,5-chlorobenzene and triazine • B3LYP/6-311++G** • signs and relative intensities agree 1440x 1440y 1600x 1600y

  19. tetraphenylporphyrin • B3LYP/6-311++G**/6-31G** • non-degenerate states only, A and B terms in one shot

  20. Summary • We can simulate MVCD • May be useful to assign modes/study molecules • Measurement – MVCD cell

  21. Uveřejněné materiály jsou určeny studentům Vysoké školy chemicko-technologické v Prazejako studijní materiál. Některá textová i obrazová data v nich obsažená jsou převzataz veřejných zdrojů. V případě nedostatečných citací nebylo cílem autora/ů záměrně poškodit event. autora/y původního díla. • S eventuálními výhradami se prosím obracejte na autora/y konkrétního výukového materiálu, abybylo možné zjednat nápravu. • The published materials are intended for students of the University of Chemistry and Technology, Prague as a study material. Some text and image data contained therein are taken from public sources. In the case of insufficient quotations, the author's intention was not to intentionally infringe the possible author(s) rights to the original work. • If you have any reservations, please contact the author(s) of the specific teaching material in order to remedy the situation.

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