Abstract
High-energy electromagnetic radiation scattering techniques havebeen used to measure the structural differences between fourisotopic samples of methanol (CH3OH, CD3OD, CH3ODand CD3OH). The first series of experiments employed roomtemperature and ambient pressure. The carbon-oxygenintramolecular bond length was measured and found to depend morestrongly on the isotopic substitution at the hydroxyl site thanat the methyl sites. The oscillations in the isotopic differenceof the x-ray structure factor, ΔSX(Q), are shown atroom temperature to be about 2% as large as theoscillations in the total structure factor. Our uncertaintiesare an order of magnitude smaller than those of previous gammaray measurements (Benmore C J and Egelstaff P A 1996 J. Phys.: Condens. Matter 8 9429-32). A second series ofexperiments was carried out at -80 °C at its vapourpressure in order to study the significant temperaturedependence of these effects. The ΔSX(Q) difference at-80 °C is shown to be up to three times larger than theroom temperature difference. These studies showed that isotopicstructural differences in methanol may be represented astemperature shifts that vary as a function of thermodynamicstate and substitution site.
Published Version
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