Excited atoms and molecules in physicochemical processes and diagnostics of nonequilibrium plasma

The role of metastable excited atoms and molecules in the mechanisms of physicochemical processes and diagnostics of quasi-equilibrium and nonequilibrium atomic and molecular electric-discharge plasmas is analyzed. The consideration is focused on the mechanism of excitation of electronic and vibronic states, as emission from these levels form optical spectra used for plasma diagnostics. The contribution of metastable excited species to other physicochemical processes: dissociation, chemical reactions involving atoms and molecules, ionization, ion-electron recombination, and ion conversion, is briefly discussed. It is shown that the participation of metastable species should be taken into account before application of spectral methods of plasma diagnostics, especially, at elevated (atmospheric and higher) pressures.