UV–NIR spectroscopy of air plasma in transverse arc discharge V. Chernyak a , L. Kernazhitsky b, * , V. Naumov b , G. Puchkovska b , V. Yukhymenko a a Radiophysical Faculty, Taras Shevchenko Kiev National University, Prospect Acad. Glushkova 2/5, Kiev 03122, Ukraine b Department of Photoactivity, Institute of Physics, National Academy of Sciences of Ukraine, Prospect Nauki 46, Kiev 03028, Ukraine Received 6 September 2004; revised 19 November 2004; accepted 30 November 2004 Available online 11 February 2005 Abstract Spectroscopic characterization of a specific case of the atmospheric pressure air plasma in the transverse arc discharge of high voltage was done. Within the spectrum of wavelengths from 200 to 1100 nm all remarkable emissions were monitored, and all excited atomic lines of N, O, H and molecular bands of NO, N 2 ,O 2 , OH, CN were identified. Using relative intensities of analytical CuI lines (a product of the electrode emission) and N 2 (C 3 P u KB 3 P g )2 C -system bands (a dominating component of the plasma-forming gas), the temperature of electronic excitation of free atoms, T exc , and the temperatures of excitation of vibrational and rotational states of molecules, T V and T R , were determined. It was found that there is no local LTE in this arc discharge air plasma during its space/time evolution, and effects of strong non- isothermality have a place. q 2005 Elsevier B.V. All rights reserved. Keywords: Air plasma; Arc discharge; Molecular spectroscopy; Electronic temperature 1. Introduction Spectroscopic characterization of air plasma in electric discharges is of permanent interest in many labs because of various important applications [1]. From the optical spectra emitted by the air plasma one can deduced all basic plasma parameters and its state [2]: composition of chemical elements (according to emitted lines), concentrations of excited atoms and molecules upon energetic levels (from the intensity of spectral lines), densities of charged and neutral particles (from the broadening of spectral lines), temperatures of excitation of atomic and molecular states (from the relative or absolute spectral line intensities). The main condition is a correct use of the spectroscopic diagnostics in every specific case, e.g. application of approximation of the optically thin plasma in conditions of high atmospheric pressure and approximation of the local thermodynamic equilibrium (LTE) in conditions of high non-isothermality when the characteristic temperatures of different plasma components may be differenced within the relation: electron temperature T e Ovibrational temperature T V Orotational temperature T R Rtranslational gas tempera- ture T g [3]. Among possible types of the non-equilibrium high- pressure discharges: spark, corona, barrier, etc [4], one specific case is very interesting. This is a transverse arc in a blowing flow with a stationary current column or with a rotating one in a vortex flow. It is an intermediate case of the high-voltage low-current self-sustained discharge with a self-adjustable arc supported by the plasma flow [5]. It differs from the non-stationary gliding arc of Czernichowski type [6,7] by the fixed arc length. It also has a convective cooling of the plasma column by the airflow but without conductive heat losses at the walls since it is a free arc jet. An intensive transverse ventilation of the arc plasma increases its ionization non-equilibrium and non-isotherm- ality [8]. This type of the arc was tested successfully in different variants with the primary and secondary discharges for the plasma-assisted processing of various homo- and heterophase gas and liquid substances [9,10]. However, despite of achievements in practical applications, there are still enough issues for research. One of the main points is a mechanism of the transition from the quasi-equilibrium to 0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2004.11.088 Journal of Molecular Structure 744–747 (2005) 871–875 www.elsevier.com/locate/molstruc * Corresponding author. Tel.: C380 44 265 9860; fax: C380 44 265 1589. E-mail addresses: chern@univ.kiev.ua (V. Chernyak), kern@iop.kiev.ua (L. Kernazhitsky).