Absolute reactive molecule densities from an argon RF atmospheric pressure plasma jet measured by quantum cascade laser absorption spectroscopy
Résumé
Summary form only given. The non-equilibrium properties of the atmospheric pressure discharges enhance specific and interesting chemistry especially that of reactive nitric-oxide species (RNOS) such as O 3 and NO x . O 3 for example has biological effects and was also utilized to sterilize non-living objects [1]. In order to investigate and control the biological reactive species produced, very accurate techniques are required. Moreover, for biomedicine applications, absolute densities have to be known in order to identify and subsequently control the biological effects. A suitable non-invasive method to identify and measure reliably the different species produced by atmospheric pressure plasma is the mid-infrared (IR) absorption spectroscopy [2]. Based on new improvement of quantum cascade laser operating at atmospheric conditions, we are able to investigate an argon radio frequency plasma jet operating in ambient air. Already known for its really good results at low pressure [3], this diagnostic has been adapted to operate at atmospheric conditions by overriding the disturbance of the dominant pressure broadening. The plasma jet is introduced through one side of a multipass cell. A measured spectrum is compared to a simulation in real time. This leads to an accurate determination of the selected molecule concentration within the cell. It is possible to reach a detection limit of 30 particles per billion (ppb) with an accuracy of 40 ppb for NO and NO 2 molecules. To the knowledge of the authors, this performance has never been reached up to now. The sensitivity of a few ppb allows us to lead further investigation of the chemistry dynamic directly resulting of the different impurities admixed within the feed gas. These impurities affect the net production rate of O 3 and NO 2 and the results will be presented as an example. This talk aims to introduce the recent interest of this diagnostic technique and its advantage to measure the plasma chemistry dynamic regarding some selected reactive species. A specific care on O 3 and NO x production will be presented. Water admixture and its effects on the studied reactive molecules will also be presented and discussed.
