Other Molecular Spectroscopic Properties: ROA, NMR, ECD

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

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 10000 atoms calculated

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

ROA Measurement

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

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

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)

NMR

Molecule in a Magnetic Field

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

NMR Shielding Computations Energy

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

NMR Spin-Spin Coupling Constants

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

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

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

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

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

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

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