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  • 1
    Electronic Resource
    Electronic Resource
    Coupling the methyl group in acetamide to phonons: a consistent view of tunnelling and lattice dynamics (1994)
    Springer
    The European physical journal 94 (1994), S. 69-77 
    Details
    ISSN: 1434-6036
    Keywords: 63.20 ; 63.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Inelastic neutron spectra of acetamide-h5 and acetamide-h2 have been measured at different temperatures below 40K and with high energy resolution in the energy range up to 15 meV. A lattice dynamical model on the basis of atom-atom potentials and electric charges obtained from first principles calculations describes the spectra well if soft internal molecular modes are included. The model is used to reproduce the temperature dependence of the tunnelling transition of the methyl group. For this purpose the density of states is split into that of an isolated rotor in a static field and that of the phonon bath. The effects of the rotor-phonon coupling are evaluated in second order perturbation theory. The broadening of tunnelling lines comes out correctly when the atom atom potentials taken from literature are scaled down by 20%. To get the shift right the strength of the coupling to the lattice needed to be different for the A type symmetry state from that for the E type state. The coupling with the low frequency phonons appears to be very weak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307656
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamical aspects of self-organized (macro) molecular systems investigated by neutron spin-echo spectroscopy (1997)
    Springer
    Colloid & polymer science 106 (1997), S. 112-117 
    Details
    ISSN: 1435-1536
    Keywords: Neutron spin-echo ; relaxation dynamics ; molecular aggregates ; microemulsions ; block copolymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Neutron spin-echo (NSE) spectroscopy is a tool to close the gap between light scattering and more conventional neutron spectroscopies. It may also be viewed as an augmentation of small-angle scattering with inelastic, dynamical information. Using a microemulsion system as example for a system of molecular aggregates and a block-copolymer system forming macromolecular aggregates, it is shown what type of dynamics is observable by NSE-spectroscopy. The lamellar phase of a SDS-pentanol-water microemulsion allows for the investigation of different layer modes (undulation, peristaltic mode) the dynamics of which are determined by elastic properties of the interface layers and by the friction due to fluid flow between the layers. Platelet-like aggregates of polyethylene-polyethylenebutylene (PE-PEP) copolymers formed upon cooling a decane solution exhibit a polymeric brush of PEP-hairs on their surface. The fluctuation dynamics of this brush determined by a balance of solvent friction and entropie restoring forces has been observed by NSE spectroscopy. Besides, the direct dynamical information the NSE data allow for the separation of static scattering due to the average structure from the scattering contributions due to mobile fluctuating parts of the sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01189503
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