Here, the frequency of the light field oscillation is determined by properties of the molecule such as atomic masses and bond strengths, which allows for an identification of the molecule. Like an antenna, the slightly electrically charged atoms in motion then radiate a light field. When the exciting field oscillations are over, the molecule continues to vibrate for a while - just like a swing after the person stops the tilting movements. Something similar happens when the alternating electromagnetic field of a short laser pulse interacts with a molecule, only about 100 trillion times faster: when the alternating field is synchronized with the vibrations between the atoms of the molecule, these vibration modes absorb more and more energy from the light pulse, and the vibration amplitude increases. This gradually adds energy to the swing, so that the deflection of the swing increases over time. It also develops and verifies a detailed quantum chemical model that can be used in the future to quantitatively predict even the smallest deviations from linear behavior.Ī child on a swing sets it in motion with tilting movements of the body, which must be synchronized with the swing movement. The study elucidates the mechanisms that fundamentally determine this energy transfer. Ioachim Pupeza (LMU/Department of Physics, MPQ) show for the first time in theory and experiment how molecules gradually absorb the energy of the ultrashort light pulse in each individual optical cycle, and then release it again over a longer period of time, thereby converting it into spectroscopically meaningful light. Regina de Vivie-Riedle (LMU/Department of Chemistry) and PD Dr. FRS, a laser spectroscopy method in which the electric field of laser pulses repeating millions of times per second is recorded with time resolution after passing through the sample, now provides even deeper insights: scientists led by Prof. Advances in ultrafast laser technology have steadily improved the level of detail in studies of such light-matter interactions. When light impinges on molecules, it is absorbed and re-emitted. The results of measurements using a recently developed frequency domain spectroscopic sensor with a spectral resolution of 1 GHz confirm the MD analysis.Scientists at the LMU and the Max Planck Institute of Quantum Optics (MPQ) have used ultrashort laser pulses to make the atoms of molecules vibrate and have gained a precise understanding of the dynamics of energy transfer that take place in the process. The existence of long lasting relaxation processes opens the possibility to directly observe and study H-bond vibrational modes in sub-THz absorption spectra of bio-molecules if measured with an appropriate spectral resolution. By studying hydrogen bond atomic displacements, it was found that the atoms are involved in a number of collective oscillations, which are characterized by different relaxation time scales ranging from 2–3 ps to more than 150 ps. Two different complimentary techniques are used in this study, one is the analysis of the statistical distribution of relaxation time and dissipation factor values relevant to low frequency oscillations, and the second is the analysis of the autocorrelation function of low frequency quasi-periodic movements. The purpose of this work is to use atomic oscillations in the 0.35–0.7 THz range, found from molecular dynamic (MD) simulations of E.coli thioredoxin ( 2TRX), to study relaxation dynamics of two intra-molecular H-bonds, O⋯H–N and O⋯H–C. The knowledge of relaxation times of atomic oscillations is critical for the successful application of THz spectroscopy for hydrogen bond characterization. Multiple resonance absorption lines have been reported. Sub-Terahertz (sub-THz) vibrational spectroscopy that combines measurements with molecular dynamics (MD) computational prediction has been demonstrated as a promising approach for biological molecule characterization. Since interactions via hydrogen bonds are weaker than covalent bonds, it can be expected that atomic movements involving H-bonds have low frequency vibrational modes. Hydrogen bonds (H-bonds) in biological macromolecules are important for the molecular structure and functions.
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