Electronic quenching of OH(A) by water in atmospheric pressure plasmas and its influence on the gas temperature determination by OH(A–X) emission

• Published in: Plasma sources science & technology 2010-02, Vol.19 (1), p.015016-015016 (7)
• Main Authors: Bruggeman, Peter, Iza, Felipe, Guns, Peter, Lauwers, Daniel, Kong, Michael G, Gonzalvo, Yolanda Aranda, Leys, Christophe, Schram, Daan C
• Format: Article
• Language: English
• Subjects: Electric discharges; Exact sciences and technology; Glow; corona; Optical (ultraviolet, visible, infrared) measurements; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma diagnostic techniques and instrumentation
• ISSN: 0963-0252; 1361-6595
• DOI: 10.1088/0963-0252/19/1/015016

In this paper it is shown that electronic quenching of OH(A) by water prevents thermalization of the rotational population distribution of OH(A). This means that the observed ro-vibrational OH(A-X) emission band is (at least partially) an image of the formation process and is determined not only by the gas temperature. The formation of negative ions and clusters for larger water concentrations can contribute to the non-equilibrium. The above is demonstrated in RF excited atmospheric pressure glow discharges in He-water mixtures in a parallel metal plate reactor by optical emission spectroscopy. For this particular case a significant overpopulation of high rotational states appears around 1000 ppm H2O in He. The smallest temperature parameter of a non-Boltzmann (two-temperature) distribution fitted to the experimental spectrum of OH(A-X) gives a good representation of the gas temperature. Only the rotational states with the smallest rotational numbers (J < = 7) are thermalized and representative for the gas temperature.