**Annotation.**

**Relevance. **In the last decade, the rapid development of solutions to the problems of preserving the planet’s energy resources and improving “artificial” photosynthesis, which arose with the development of science and technology, have required the creation of effective sources of spectral radiation that simultaneously emit bands and lines in given spectral ranges. It is relevant to find ways to increase the radiation power of spectral bands in the violet-blue and blue-green spectral ranges.

**Purpose. **The purpose of the study was to determine the plasma parameters in mixtures of diiodide, dibromide and mercury dichloride vapours with helium at which the maximum value of the radiation power was obtained in the experiment and to find their values at which the radiation power in the spectral bands can be maximum.

**Methods.** The parameters of the plasma discharge were determined by a numerical method based on finding the value of the electron energy distribution function (EEDF). EEDF was determined by solving the kinetic Boltzmann equation in a binomial approximation using the Bolsig+ programme. On the basis of EEDF, the average electron energies, electron mobility, specific losses of discharge power for elastic and inelastic processes of electron collisions with mixture components, and constants of elastic and inelastic electron scattering velocities were found.

**Results. **The results of studies of the parameters of a gas-discharge plasma barrier discharge on a mixture of vapours of diiodide, dibromide and mercury dichloride with helium depending on the reduced electric field strength (E/N) are presented. The value of the average energy, drift velocity, concentration and temperature of electrons is in the range: 0.31 EV -24.2 EV, 2.8 ⋅ 10^{5} m/s – 2.0 ⋅ 10^{5} m/s, 5.9 ⋅ 10^{18} m^{-3} – 8.3 ⋅ 10^{18} m^{-3}, 3,644.7 – 278 632 ^{о}K when changing the E/N parameter from 1 to 200 Td. Dissociative excitation rate constants B^{2}Σ – the state of the exciplex molecules of monobromide, monoiodide and mercury monochloride by electrons reached a maximum value of 2.03 ⋅ 10^{-14} m^{3}/c, 3.39 · 10^{-14} m^{3}/s and 3.44 · 10^{-15} m^{3}/c for the reduced electric field is 97.07 Td, respectively. The losses of specific discharge power reach the maximum of 11.4%, 29.5%, 40.7%, 4.9% and 3.1% for values of the E/N parameter equal to 14.7 Td, 7.8 Td, 26.1 Td, 15 Td and 15 Td for electronic state of mercury monobromide B^{2}Σ^{+}_{1./2 }X^{2}Σ^{+}_{1/2}, mercury dibromide (HgBr_{2} (D)) and B^{2}Σ^{+}_{1./2} states of mercury monoiodide and mercury monochloride, respectively.

**Conclusions. **The results of numerical modelling give grounds to conclude that it is possible to improve the energy characteristics of gas-discharge emitters based on a mixture of vapours of diiodide, dibromide and mercury dichloride with heliumand by reducing the reduced electric field strength to a value of 26.1 Td

**Keywords:** low-temperature plasma, mercury diiodide vapours, mercury dibromide vapours, mercury dichloride vapours exciplex molecules, plasma parameters

** https://doi.org/10.24144/2415-8038.2021.50.9-14**