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FIZIKA A 14 (2005) 2, 219 - 224
 
ASYMMETRIC PROFILE OF THE TOTALLY SYMMETRIC STRETCHING BAND IN RAMAN
SPECTRA OF BIS(TRIMETHYLSILYL)ACETYLENE
VLASTA MOHAČEK-GROŠEV and KREŠIMIR FURIĆ
Ruđer Bošković Institute, POB 180, 10002 Zagreb, Croatia
Received 26 January 2005; Accepted 28 November 2005
Online 7 December 2005
The asymmetric band profile of the triple C = C stretching Raman band in
bis(trimethylsilyl)acetylene was decomposed into a higher and a lower wavenumber part,
each described as one half of a Lorentzian bandshape with its own halfwidth (Ghigh and Glow), but with common band centre and maximum point. Ghigh and Glow were fitted at seventeen different temperatures ranging
from 110 K to 323 K (the melting point occurring roughly at 290 K). It was found that
lower wavenumber side of the band was considerably broader than the higher wavenumber
side, throughout the whole temperature interval chosen. This unexpected crystal-band
asymmetry, present together with the "normal" phonon spectrum, seems to indicate
a freezing of orientational disorder of methyl groups, while molecular centres of mass
remain positioned on the Bravais lattice - like in the case of the so called glassy
crystals. The asymmetry of the band above 290 K suggests the existence of a nonisotropic
liquid state.
PACS numbers: 78.30.-j, 61.43.-j, 63.30.-e, 63.50.rx
UDC 535.375.5, 532.74, 539.194
Keywords: Raman spectra, bis(trimethylsilyl)acetylene, low temperature, disorder,
glassy crystal
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