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Content archived on 2024-06-16

Real-time study of chemical events by ultra-fast IR measurements: unimolecular conformational dynamics and solute solvent interactions

Final Activity Report Summary - ULTRA-FAST/IR (Real-time study of chemical events by ultra-fast IR measurements: unimolecular conformational dynamics and solute solvent interactions)

In this project a modern laser spectroscopic measurement setup was developed which was subsequently used to investigate fundamental dynamical processes of molecules in liquid and solid state. The developed ultrafast infrared laser spectrometer can be used to record the infrared spectrum of a studied system with a time resolution of four hundred femtoseconds (0.0000000000004 s).

Infrared spectrum of a substance is like a molecular fingerprint and it can be used to identify a compound. It is also very sensitive to the molecular structure and interactions with the environment, and thus can be used to study structural changes in molecules. The rates of chemical reactions and other photophysical and photochemical phenomena depend on how energy is dissipated and relaxed. Studies of the energy relaxation/dissipation dynamics are therefore of crucial importance to understand chemical processes. The built setup was used to investigate energy relaxation processes in transition metal complexes in liquid phase, in particular, Fe(acac)3 and Cr(acac)3. Molecules were excited by UV laser pulses after which the transient IR spectrum was used to monitor the state of the system as a function of time. In both cases the vibrational energy relaxation timescales were directly measured and a model for the full electronic and vibrational energy relaxation chain was constructed revealing new important information on their relaxation dynamics.

Another target of investigation was a copper compound Cu(dmphen)2 which has been proposed to be a potential candidate for a "molecular switch". An important property of the molecule is that it changes its structure when it is excited with light. New information on the mechanisms of this light induced structural change was obtained in this project.

One more compound studied in this project was formic acid (FA) and its dimer. FA is the simplest carboxylic acid and it is a very important molecule in nature and in industry. FA exists in two structurally different forms and they can be interchanged by infrared irradiation. On the other hand, the dimerisation of carboxylic acid provides a mechanism for "molecular recognition" which determines the 3-dimensional structure of many macromolecules. The energy relaxation dynamics of monomeric and dimeric FA were studied in low temperature rare gas matrices.