engleski

Spectroscopic arguments for a new crystal phase of glycolaldehyde

In an attempt to elucidate the nature of glycolaldehyde dimer solid phases further, low temperature Raman spectroscopy was employed and phonon spectra recorded in the temperature interval from 10 K - 300 K. It seems probable that the a phase of glycolaldehyde dimer belongs to P21/n space group with Z = 2, the same crystal class in which 1, 4-dioxane and DL-glyceraldehyde crystallize. Studying the temperature dependence of glycolaldehyde dimer a phase low frequency Raman bands, one observes an increase in the number of phonons from six to thirteen when the sample is cooled below 80 K. We suggest that a phase transformation into a new phase g takes place, with the number of molecules per unit cell probably equal to Z = 4. Normal coordinate analysis was performed for glycolaldehyde dimer with two equatorial as well as for dimer with two axial hydroxyl groups, in order to predict the number of internal modes falling in the phonon region. If there were any centrosymmetric dimers with two axial hydroxyl groups present, than a band around 150 cm-1 would have been expected in Raman spectrum, which was not observed. This is thus far the strongest argument in favour of hypothesis that the phase a consists of dimers with two equatorially placed hydroxyl groups.

glycolaldehyde ; dioxane ; Raman ; infrared ; crystal structure ; glyceraldehyde

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