In this work, the effects of the plasma chemistry of an argon microwave (2.45 GHz) discharge at reduced pressure on the conversion of three different alkanes (n-pentane, n-hexane and n-heptane) have been studied. Optical emission spectroscopy has been used for identifying the species generated in the plasma and for estimating its gas temperature. Gas chromatography, mass spectrometry, X-ray diffraction and FTIR spectroscopy have been employed for identifying and analyzing all the compounds present as reaction products. Microwave power and hydrocarbon flow rate have been found critically to affect both conversion and selectivity. The main gas products have been hydrogen and ethylene. At low powers (100-150 W) the conversion to hydrogen has been quite selective. However, at high powers (>300 W) or slow hydrocarbon flow rate ethylene has resulted to be the major product. In most cases, an important fraction of a carbon deposit has been obtained which has been characterized as an amorphous hydrogenated carbon film. Some plausible mechanisms explaining the formation of the main reaction products have been discussed. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.