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Publications in Scientific Journals:

C. Mitterdorfer, J. Bernard, F. Klauser, K. Winkel, I. Kohl, K. Liedl, H. Grothe, E. Mayer, T. Loerting:
"Local structural order in carbonic acid polymorphs: Raman and FT-IR spectroscopy";
Journal of Raman Spectroscopy, 43 (2012), 108 - 115.



English abstract:
Two different polymorphs of carbonic acid, a- and b-H2CO3, were identified and characterized using infrared spectroscopy (FT-IR) previously. Our attempts of determining the crystal structures of these two polymorphs using powder and thin film X-ray diffraction
techniques have failed so far. Here, we report the Raman spectrum of the a-polymorph,compare with its FT-IR spectrum and present band assignments in line with our work on the b-polymorph [Angew. Chem. Int. Ed. 48 (2009) 2690-2694]. The Raman spectra also contain
information in the wavenumber range ~90-400 cm-1, which was not accessible by FT-IR spectroscopy in previous work. While the -polymorph shows Raman and IR bands at similar positions over the whole accessible range, the rule of mutual exclusion is obeyed for the b-polymorph. This suggests that there is a center of inversion in the basic building block of b-H2CO3, whereas there is none in a-H2CO3. Thus, as the basic motif in the crystal structure we
offer the cyclic carbonic acid dimer containing a center of inversion in case of b-H2CO3 and a catemer-chain or a sheet-like structure based on carbonic acid dimers not containing a center of inversion in case of a-H2CO3. This hypothesis is strengthened when comparing Raman
active lattice modes at < 400 cm-1 with calculated Raman spectra for different dimers. In particular, the intense band at 192 cm-1 in b-H2CO3 can be explained by the inter-dimer stretching mode of the centrosymmetric RC(OHO)2CR entity with R=OH. The same entity
can be found in gas-phase formic acid (R=H) and in b-oxalic acid (R=COOH) and produces an intense Raman active band at very similar frequency. The absence of this band in a-H2CO3 confirms that the difference to b-H2CO3 is found in the local coordination environment and/or monomer conformation rather than on the long range.


"Official" electronic version of the publication (accessed through its Digital Object Identifier - DOI)
http://dx.doi.org/10.1002/jrs.3001


Created from the Publication Database of the Vienna University of Technology.