Introduction. In our previous studies have been found that in barrier discharge plasma based on mercury diiodide vapor with helium and nitrogen mixture mercury monoiodide exciplex molecules are formed. Emission of these molecules is occurring in violet-blue spectral range (λmax. = 444 nm) and have been revealed that only a mixture of mercury diiodide vapor with helium is more efficient (radiation power in spectral band with a peak wavelength 444 nm was two times higher than in a mixture with the addition of nitrogen). It has been suggested that the reason of radiation power decrease was due to changing parameters of gas-discharge plasma at the addition to the mixture of nitrogen.
Purpose. The aim of research was to determine the plasma parameters in mixtures as mercury diiodide vapor with helium as well as nitrogen addition for the values of mixture components partial pressures at which in the experiment the maximum value of the radiation power was obtained.
Methods. Barrier discharge plasma parameters were determined numerically based on the electron energy distribution function (EEDF) in discharge. EEDF was determined by solving the kinetic Boltzmann equation in two-terms approximation using well-known program "Bolsig +". Based on EEDF: mean electron energies, electron mobility, specific power losses of electrical discharge and rate constants of elastic and inelastic scattering of electrons on mercury diiodide, nitrogen molecules and helium atoms as a function of the reduced electric field were identified.
Results. Established: electron energy distribution functions, transport characteristics, specific losses of discharge power on electronic processes and rate constants of processes: elastic and inelastic scattering of electrons on the components of the mixture depending on the value of the reduced electric field. For mercury diiodide vapor, helium and nitrogen mixture maximum values of the electron density vary from 2.2·1018 m-3 to 4.5·1018 m-3 by changing the value of the parameter E/N from 1 Td to 100 Td. Electron temperature increased from 6960 K to 148,480 K. Portion of discharge power, that is spent on the process of mercury monoiodide molecules excitation reached a maximum of 5.5% at the value of the parameter E/N equal to 12 Td for B2Σ+1/2 electronic state. The rate constant of B2Σ+1/2 –state excitation is equal to (1.4-2.3) 10-14 m3/c for the reduced electric field E/N = 25-75 Td, at which in experimental conditions maximum radiated power in violet - blue spectral region (λmax. = 444 nm) was observed. For the mixture without nitrogen was significant difference in the portion of discharge power that is spent on the process of excitation of mercury monoiodide molecules by electrons. It reached a maximum of 12% at the value of the parameter E / N equal to 9 Td.
Conclusion. For a mixture of mercury diiodide vapor and helium mean electron energies, portions of discharge power on processes of mercury monoiodide exciplex molecules excitation by electrons, rate constant of the process that leads to the formation of mercury monoiodide molecules are higher because the radiation power of mercury monoiodide exciplex molecules in the mixtures of mercury diiodide vapor with helium, which was measured in experimental studies is higher (twice) than in mercury diiodide vapor , helium and nitrogen mixture. Gas-discharge radiation source of violet-blue spectral range, the working medium of which is barrier discharge plasma based on mercury diiodide vapor, nitrogen and helium mixture can be used in scientific researches in biotechnology, photonics, medicine, as well as for discharge indicator panels creation
Keywords: gas-discharge plasma, radiation of exciplex molecules, visible spectral range, plasma parameters, diiodide