Unraveling molecular vibrational energy pathways by laser diagnostics and computer simulations

Chemical reactions occur due to energy accumulation in specific vibrational intramolecular degrees of freedom (dofs). Thus, vibrational energy redistribution among different dofs inside a molecule as well as intermolecular vibrational energy transfer to external dofs is of particular importance for chemical reactions. In many cases these processes take place on a picosecond time scale such that short pulse lasers may be used to excite vibrations and analyze microscopic vibrational processes in a media. The process of photodissociation of organic peroxides carbon dioxide is formed with a broad vibrational energy distribution disposed mainly in the bend and symmetric stretch vibrational degrees of freedom. The highest frequency asymmetric stretch mode seems to remain unexcited because in all the solvents its vibrational relaxation is very slow. Comparatively fast vibrational cooling of CO₂ is insured by the Fermi resonance between the bend and symmetric stretch vibrations and proceeds through V-V near resonant energy transfer to solvent molecules.