Serdecznie zapraszamy na Seminarium Wydziałowe, w trakcie którego profesor Yukihiro Ozaki z Kwansei Gakuin University (Japonia), doktor honoris causa Uniwersytetu Jagiellońskiego, wygłosi wykład zatytułowany:
"Anharmonicity and NIR spectroscopy"
Seminarium odbędzie się w poniedziałek 10.12.2018 r., o godzinie 10:00, w sali A0-04, na Wydziale Chemii.
Investigations of entire NIR spectra based on quantum chemical calculations remained very rare because of the markedly increased complexity of theoretical description of the anharmonic effects. The formalism of quantum harmonic oscillator allows only transitions between neighbor vibrational levels due to orthogonality of eigenfunctions of harmonic oscillator. Thus, it is impossible to describe overtone modes by harmonic approximation. Furthermore, the quantum harmonic formalism, which does not include mode coupling, cannot describe combination modes. Therefore, any theoretical approaches applicable to NIR spectroscopy must be beyond harmonic approximation.
For this purpose, one can find a few comprehensive anharmonic approaches. The vibrational self-consistent field (VSCF) approach is a variational approach, one of the first widely implemented anharmonic methods. Further developments of the method have brought about, such as perturbation corrected VSCF (PT2-VSCF), which addresses the above problem. These improvements, however, increased the computational cost significantly. The vibrational configuration interaction (VCI) approach, which describes the coupling adequately and is highly accurate, is another possibility. Second-order vibrational perturbation (VPT2) theory combines good accuracy and resource affordability. Unfortunately, it had the typical shortcoming of incorrect description of tightly coupled modes, i.e., vibrational resonances, and thus, to address these issues generalized VPT2 approach (GVPT2) has recently been introduced. This approach may be utilized for general theoretical NIR studies of even complex molecules.
By using GVPT2 we have succeeded in calculation NIR spectra of many compounds including long-chain fatty acids.