Multi-frequency e.p.r. studies of Argonne and Illinois sample bank coals

✍ Scribed by R.B. Clarkson; Wei Wang; D.R. Brown; H.C. Crookham; R.L. Beiford

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 676 KB
• Volume: 69
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(90)90122-7

✦ Synopsis

Eight coals from the Argonne Premium Coal Sample Program (APCSP), and an Illinois No. 6 coal from the Illinois Coal Basin Sample Program (ICBSP) have been investigated, employing a novel very high frequency (VHF) e.p.r. spectrometer operating at a microwave frequency of about 95 GHz and a magnetic field of 3.4 Tesla. Macerals separated from the ICBSP sample by density gradient centrifugation were also investigated. The high fields used in these experiments provide a IO-fold improvement in the dispersion of electronic Zeeman terms over that provided by conventional X-band instruments (9.5 GHz; 0.34 T), enabling us to resolve spectral features not seen at lower frequencies. Model compounds (perylene( +) and dibenzothiophene(+) radicals) were also studied for comparison purposes. It is proposed that low-field peaks in some of the coal and maceral VHF e.p.r. spectra are the result of spin-orbit coupling of unpaired electrons to heteroatoms, primarily sulphur, and this effect is modelled theoretically employing a simple, two-species model. Preliminary pulsed e.p.r. data on a separated fusinite taken at S-band (3 GHz) are also presented to support the electron exchange model for the lineshape of this maceral.