Abstract
The enormous versatility in the properties of carbon materials depends on the content of the sp2 and sp3 covalent bonds. Under compression, if intermolecular distances cross a critical threshold, then unsaturated hydrocarbons gradually transform to saturated carbon polymers. However, the mechanism of polymerization, even for benzene, the simplest aromatic hydrocarbon, is still not understood. We used high-pressure synchrotron X-ray, neutron diffraction, and micro-Raman spectroscopy together with density functional calculations to investigate the isotope effects in benzene isotopologues C6H6 and C6D6 up to 46.0 GPa. Raman spectra of polymeric products recovered from comparable pressures show the progression of polymerization exhibiting a pronounced kinetic isotope effect. Kinetically retarded reactions in C6D6 shed light on the mechanism of polymerization of benzene. We find that C6D6-derived products recovered from P < 35 GPa actively react with moisture, forming polymers with higher sp3 hydrogen contents. Significant isotopic shift (≥7 GPa) in persistence of Bragg reflections of C6D6 is observed.
| Original language | English |
|---|---|
| Pages (from-to) | 1856-1864 |
| Number of pages | 9 |
| Journal | Journal of Physical Chemistry Letters |
| Volume | 8 |
| Issue number | 8 |
| DOIs | |
| State | Published - Apr 20 2017 |
Funding
The experimental works were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. Beam time for these experiments was provided by the Carnegie-DOE Alliance Center, which is supported by DOE-NNSA under grant number DE-NA-0002006. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974 and DOE-BES under Award No. DE-FG02-99ER45775, with partial instrumentation funding by NSF. The APS is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Measurements were performed at the high-pressure beamline 12.2.2 ALS, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Research conducted at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division Office of Basic Energy Sciences, U.S. Department of Energy. Research in the University of Utah is supported by American Chemical Society grant PRF no. 55176-ND10. J.K.H and M.C.M research is supported by NSF-REU grant number 1263394. Travel support for J.K.H. is funded by the Undergraduate Research Office of the University of Utah.