Optical emission spectra of microwave discharge in different liquid hydrocarbons

• Published in: Plasma processes and polymers 2020-08, Vol.17 (8), p.n/a
• Main Authors: Lebedev, Yuri A., Shakhatov, Viatcheslav A.
• Format: Article
• Language: English
• Subjects: Aromatic hydrocarbons; Atmospheric models; Clusters; Cyclohexane; discharges in liquid hydrocarbons; Emission analysis; Emission spectra; Heptanes; Hydrocarbons; Liquid surfaces; Microwave discharge; optical emission spectroscopy; Toluene; Xylene
• ISSN: 1612-8850; 1612-8869
• DOI: 10.1002/ppap.202000003

Emission spectra of microwave discharge in liquid hydrocarbons (hexane (C6H14), n‐heptane (С7Н16), decane (С10Н22), pentadecane (C15H32), cyclohexane (С6Н12), toluene (С6Н5–СН3), ortho‐xylene (С6Н5–(СН3)2), and petroleum solvent nefras S2 80/120 [mixture of light hydrocarbons with boiling temperature ranging between 33°C and 205°C]) were studied in the range of wavelength 200–700 nm. The pressure above the surface of the liquid was equal to the atmospheric pressure. It was shown that in the spectra measured in aromatic hydrocarbons (toluene and ortho‐xylene) the sequence of the Swan band with Δυ = 0 was overlapped with the molecular emission band with a maximum at 511 nm never observed before. Analysis of known data allowed us to hypothesize that this emission can be attributed to the emission of linear carbon cluster C5 (transitionC5(1Πu→X1Σu+)). This cluster was previously observed only in absorption. Rotational temperatures determined by modeling of the sequence Δυ = −1 of the Swan band were equal to 2,000 ± 300 K for all studied hydrocarbons. Microwave plasma in liquid hydrocarbons is a new area of plasma physics and plasma processing. In this paper, we focus on the characterization of emission spectra of a microwave discharge in different liquid hydrocarbons (alkanes, cyclic, and aromatic hydrocarbons). In the spectra measured in an aromatic hydrocarbon (toluene, ortho‐xylene), the sequence of the Swan band with Δυ = 0 was overlapped with the unknown molecular band emission with a maximum at 511 nm. Analysis brings us to the conclusion that this emission can be caused by emission of the linear carbon cluster C5. This cluster was previously observed only in absorption. This means that microwave discharge in liquid aromatic hydrocarbons produced specific conditions for C5 generation and its emission.