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Vibrational Levels (vibrational + level)
Selected AbstractsOn the Influence of the Local Environment on the CO Stretching Frequencies in Native Myoglobin: Assignment of the B-States in MbCOCHEMPHYSCHEM, Issue 10 2006Markus Meuwly Prof. Dr. Frequency shifts: The influence of the local electrostatic environment on the ground vibrational level of photodissociated CO in native myoglobin is investigated by performing QM/MM calculations at the DFT level. The distribution of CO frequencies in the FeCO conformation occurs at higher wavenumbers than in the FeOC conformation (see figure). [source] Mechanistic investigation of vibrational fine structure in e-H2 scattering using local complex potential-based time dependent wave packet approachINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2008Manabendra Sarma Abstract The structural features of vibrational excitation cross-sections in resonant e-H2 scattering have been investigated using a time dependent wave packet approach and a local complex potential to describe the 2, H anion. An analysis of the partial contributions to the vibrational excitation cross-sections reveals that all features of the excitation profile result from simple interference between bound vibrational levels of H2 and H. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Heavy atom motions and tunneling in hydrogen transfer reactions: the importance of the pre-tunneling stateJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2010Hans-Heinrich Limbach Abstract Arrhenius curves of selected hydrogen transfer reactions in organic molecules and enzymes are reviewed with the focus on systems exhibiting temperature-independent kinetic isotope effects. The latter can be rationalized in terms of a ,pre-tunneling state' which is formed from the reactants by heavy atom motions and which represents a suitable molecular configuration for tunneling to occur. Within the Bell,Limbach tunneling model, formation of the pre-tunneling state dominates the Arrhenius curves of the H and the D transfer even at higher temperatures if a large energy Em is required to reach the pre-tunneling state. Tunneling from higher vibrational levels and the over-barrier reaction via the transition state which lead to temperature-dependent kinetic isotope effects dominate the Arrhenius curves only if Em is small compared to the energy of the transition state. Using published data on several hydrogen transfer systems, the type of motions leading to the pre-tunneling state is explored. Among the phenomena which lead to large energies of the pre-tunneling state are (i) cleavage of hydrogen bonds or coordination bonds of the donor or acceptor atoms to molecules or molecular groups in order to allow the formation of the pre-tunneling state, (ii) the occurrence of an energetic intermediate on the reaction pathway within which tunneling takes place, and (iii) major reorganization of a molecular skeleton, requiring the excitation of specific vibrations in order to reach the pre-tunneling state. This model suggests a solution to the puzzle of Kwart's findings of temperature-independent kinetic isotope effects for hydrogen transfer in small organic molecules. Copyright © 2010 John Wiley & Sons, Ltd. [source] Degenerate and two-color resonant four-wave mixing applied to the rotational characterization of high-lying vibrational states of formaldehyde (Ã, 1A2),JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006M. Tulej Abstract Degenerate and two-color resonant four-wave mixing techniques (DFWM and TC-RFWM) are applied to determine rotational constants of high-lying vibrational levels in the first excited singlet state Ã(1A2) of formaldehyde. It has been demonstrated that the sensitivity of the spectroscopic technique is applicable to the low-density environment of a supersonic molecular beam and to predissociating transitions displaying low fluorescence quantum yield. In addition, we take advantage of the superior selectivity of the double-resonance method, TC-RFWM, to isolate and assign transitions in the congested region of the (one-color) DFWM spectra. The line positions of 25 well-isolated transitions are determined in the band and yield the rotational constants A, B, C and the origin ,e. The accuracy of the constants is determined by performing the same procedure for the band where literature data is available for comparison. Copyright © 2006 John Wiley & Sons, Ltd. [source] Gaseous Ion Activation Dynamics: The Role of the Bulk Gas in the Racemization of Chiral Oxonium IonsCHEMPHYSCHEM, Issue 10 2004Antonello Filippi Dr. Abstract The kinetics of the inversion of configuration of a family of chiral oxonium ions, that is, O-protonated 1-aryl-1-methoxyethanes [YMe+], were investigated in two different gaseous media (in CH3X with X=F and X=Cl) at 720 torr of pressure and in the temperature range: 25,140,°C. The activation parameters of the [YMe+] inversion reaction were found to obey two different isokinetic relationships (IKR), depending on the nature and the position of the substituents in the oxonium ions and on the nature of the bulk gas employed. The observation of two IKR for the same family of reactions was related to a switchover in the resonant vibrational energy exchange between the reactants' critical mode, active in the transition state (,), and the discrete vibrational levels , of the bulk gas. In CH3F, this vibrational,vibrational coupling switchover concerns the out-of-plane CF,,,HO bending (the , family) and the H3CF stretching (the , family) modes in the proton-bound [CH3F,YMe+] complex. In CH3Cl, the coupling switchover concerns the out-of-plane CCl,,,HO bending (the , family) and the H3CCl methyl group rocking (the , family) modes in the proton-bound [CH3Cl,YMe+] complex. The [YMe+] activation dynamics also determine the inversion dynamics. The [YMe+]ret,[YMe+]invisomerization for the , family involves the same "thermodynamically most favorable" transition state in both the CH3F and the CH3Cl media, whereas the same process for the , family proceeds through different, dynamically favored transition states. [source] | ||||||||||