Other Molecular Spectroscopic Properties: ROA, NMR, ECD

Prezentace na téma: "Other Molecular Spectroscopic Properties: ROA, NMR, ECD"— Transkript prezentace:

1 Other Molecular Spectroscopic Properties: ROA, NMR, ECD

2 (Vibrational) Raman Optical Actvity (V)ROA
Spectra from Charles University, Prague

3 ROA - history 1960/1970 – theoretical predictions
1973 first ROA - Barron, Bogaard, Buckingham 1980/90s usable ROA computations 2005 commercial ROA 2015 ROA of molecule with atoms calculated

4 ROA - physics Two-photon process Beyond dipole w w ’

5 ROA Measurement

6 ROA - calculation N4 Small rigid non-polar molecules
Polar molecules ... solvent model Flexible molecules ... conformational weighing N4 Large molecules ... ab initio limit

7 ROA - calculation Small rigid non-polar molecules
Polar molecules ... solvent model Flexible molecules ... conformational weighing Large molecules ... ab initio limit Bio-molecules, surfaces ...

8 ROA in Gaussian: Simple
freq=ROA DFT e.g. B3LYP/6-31G** usually works GIAO used by default need to optimize geometry first (as for IR, Raman, VCD)

9 NMR

10 Molecule in a Magnetic Field

11 Molecule in a Magnetic Field
Energy Magnetic Field shielding tensor Isotropic samples (solutions) – isotropic shielding Chemistry: NMR (chemical) shift:

12 NMR Shielding Computations
Energy

13 NMR Shielding Computations
Gaussian: NMR keyword HF level OK, DFT similar GIAO as default

14 NMR Spin-Spin Coupling Constants

15 Spin-Spin Coupling Constant Computations
Energy spin-spin coupling tensor isotropic samples: rotational average

16 Four Terms of Spin-Spin Coupling Constant Computations
Gaussian: NMR=SpinSpin HF not enough DFT ok

17 (Electronic) Circular Dichroism (E)CD
Excited electronic states needed Quantum Chemistry: FCI, CIS, CISD, MCSCF, CAS, CASSD, .... Most frequent: TDDFT

18 ECD Simulations Gaussian: TD=(nstates=20, singlets)
GIAO not used -> prefer gradient formulation Other programs (Dalton, etc.) – GIAO possible Accuracy: very variable, also for ORD

19 Rem.: Solvent Models dipolar approximation (L. Onsager, 1936)
cavity/dielectric models cluster/MM/QM models Gaussian: SCRF=(PCM, CPCM, etc.)

20 Rem.: Solvent Models Combination of models – various accuracy levels

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