New chemical reactions in methane at high temperatures and pressures

Abstract

The authors have used a Merrill-Bassett diamond anvil cell and Raman spectroscopy to study methane at high pressures (up to 13 GPa) and high temperatures (up to 912 K). At 2.5-5.0 GPa and 912 K, methane photoreacts with the laser light used for Raman spectroscopy and forms a graphitelike soot compound. At room temperature and pressure the Raman spectrum of the new material has an intense peak with a frequency of 1597 cm[sup [minus]1]. At higher pressures and temperatures (10-13 GPa and 948 K) a sample of [sup 13]CD[sub 4] methane photoreacted with the laser light and formed a hard, clear, solid film. At 0.34 GPa and 300 K, this film had Raman peaks at 541 and 1605 cm[sup [minus]1]. The 541-cm[sup [minus]1] peak may correspond to the 550-cm[sup [minus]1] peak found in some diamondlike carbon (DLC) films formed by chemical vapor deposition (CVD), but the 1605-cm[sup [minus]1] peak does not appear to have any such counterpart. Other possible Raman peaks were masked by interference from the diamond anvils. Thus, while the hard, clear film has some similarities to CVD DLC films, some important differences and questions remain. 35 refs., 5 figs.