Effect of impurity molecules on the low-temperature vibrational dynamics of polyisobutylene: Investigation by single-molecule spectroscopy
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Examples of the temperature dependences of SM linewidths and corresponding fits with Eq. (3) for three tetra-tert-butylterrylene molecules (a) and two dibenzoanthanthrene molecules (b) in amorphous polyisobutylene. The structure formulas of the dyes are shown as insets.
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Energy spectra of the LFMs in amorphous polyisobutylene (molecular weight of 420 000 g/mol) doped with dibenzoanthanthrene (gray histogram, 155 single molecules) and tetra-tert-butylterrylene (hatched histogram, 281 single molecules) as measured by SMS (this study), and the boson peak as measured in pure polyisobutylene by inelastic neutron scattering (solid line) (Ref. 34). Both distributions were rescaled in the following way: In order to highlight the vibrational density of states exceeding the Debye spectrum, the SMS and neutron scattering data have been plotted as , where is the density of states. Moreover, the SMS data were divided by the Bose factor (for details see text). The dashed line shows the contribution of the Debye spectrum (i.e., the sound waves) in the case of the neutron scattering data. The arrow indicates the value of the “effective” LFM frequency in the system TBT/PIB as measured with the photon echo technique (Ref. 4).
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