ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Incoherent neutron scattering (INS) experiments were performed on semioriented samples of n-nonadecane C19H40 and of the selectivity deuterated derivatives CD3–C17H34–CD3 and C2D5–C15H30–C2D5 over a wide temperature range, in particular, over the domain of existence (295–305 K) of the disordered "rotator phase'' RI. From analyses of the inelastic and quasielastic parts of the spectra, we were able to discriminate between motions parallel or perpendicular to the main long-chain axis. In the low frequency region (0–300 cm−1), numerous lattice and internal vibrational modes, showing pronounced polarization effects, were assigned. In the quasielastic regions, large broadenings were observed in the RI phase, providing clear evidences of both fast restricted translational motions along the chain axis and uniaxial rotational diffusions. For the rotational process, we have elaborated and made use of a model of diffusion for a particle in a twofold potential. Finally, the INS spectra of C19H40 in the RI phase and of C23H48 and C24H50 in their RII phases were compared and nicely interpreted within an unique model of "effective potential'' by fitting the barrier heights against rotational diffusion. All these results are discussed and compared to literature data.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457015
