»ã±¨ÌáÒª£º Vibrational, electronic, and resonance spectroscopies play a prominent role for the non-invasive experimental characterization of static and dynamic properties of molecular systems in their proper environmental conditions. However, the interpretation of most experimental spectra is difficult due to their inherent complexity, a task which can be greatly simplified with the help of theory and modelling. In fact, computational spectroscopy has shown to be a valuable tool to help unravel the various contributions to the spectrum, allowing for a better understanding of the underlying phenomena. Moving from the common practice of extracting numerical data from experiment, often with the help of simplified models, to be compared with quantum mechanical (QM) results toward a direct vis-à-vis comparison of experimental and simulated spectra strongly reduces any arbitrariness in the analysis of complex experimental outcomes and allows for a proper account of the information connected to the spectral band-shapes.
In this context, I will present strategies for the setup of a robust and versatile so-called ”virtual multifrequency spectrometer” (VMS) aimed at simulating absorption, emission and scattering spectra over a large energy range (IR, UV-Vis, X-ray). In VMS, anharmonic vibrational spectra including overtones and combination bands are computed through second-order perturbation theory [1-4], while electronic spectra line-shapes are simulated with full account of the vibrational structure and major anharmonic effects [1-2,4-5]. Vibrational effects on the molecular structure and properties are also taken into account, providing a direct link to the rotationally resolved spectra and accurate equilibrium structures of molecular systems of increasing size and flexibility [6]. The input data necessary to compute the spectra are provided by integrated computational approaches [4] built on QM methods, including hybrid QM/QM′ models.
The possibilities such a tool provides to the understanding of vibrational (Infrared, Raman, Vibrational Circular Dichroism) and UV-vis (absorption, emission, Electronic Circular Dichroism) spectra will be highlighted by the study of diverse molecular systems of increasing complexity: from isolated molecules and weakly bonded complexes/clusters to biomolecules or hybrid supra-molecular systems in complex environments [1-6]. It will be shown that computed spectra can profitably complement the data provided by their experimental counterparts, often solving also some interpretative ambiguity, and facilitating to retrieve from experimental outcomes information on structure and basic physico-chemical properties of molecular systems at microscopic level.