THE BEHAVIOR OF MOLECULES IN MICROWAVE-INDUCED PLASMAS STUDIED BY OPTICAL-EMISSION SPECTROSCOPY - 1 - PLASMAS AT ATMOSPHERIC-PRESSURE

The behavior of molecules in different atmospheric microwave-induced p lasmas (MIPs) has been studied by means of optical emission spectrosco py. This is in order to obtain more insight into molecular processes i n plasmas and to investigate the feasibility of emission spectroscopy for the analysis of molecular compounds in gases, e.g. flue gases. Var ious molecular species (i.e. N-2, CO2, H2O, SF6 and SO2) have been int roduced into discharges in argon or in molecular gases such as carbon dioxide or nitrogen. The plasmas were created and sustained by a guide -surfatron or a torch in the power range of 150 W to 2 kW. Only nitrog en sometimes yielded observable emission from the non-dissociated mole cule (first and second positive system). Using other molecular gases, only dissociation and association products were observed (i.e. atomic species and diatomic molecules such as CN, C-2, CO, OH, NH and N-2(+)) . The intensities of these products have been studied as a function of the concentration of introduced molecules, the position in the plasma and the composition of the plasma environment. Since in most cases th e same diatomic association products are seen, observed associated mol ecules can only to some extend be related to the molecules originally present in the plasma gas. Therefore, it will be difficult to use atmo spheric microwave discharges for the analysis of gas mixtures under th e experimental conditions studied. (C) 1998 Elsevier Science B.V. All rights reserved.