Spectroscopy techniques and the measurement of molecular radical densities in atmospheric pressure plasmas

Abstract

Cold atmospheric pressure plasmas (CAPs) are finding an increasing number of applications in diverse fields such as sterilization, medicine and dentistry, because they induce chemical reactivity at nearambient temperature. These plasmas are usually generated in noble gas flows which propagate into air, resulting in the production of a wide variety of species which can cause primary and secondary chemistry in both the gas and liquid phases. Detailed understanding of this low temperature reactivity requires selective and sensitive measurements of radical species. In this review we focus upon several techniques from a methodological point of view that are suitable for the sensitive detection of reactive species, or show promise for this purpose. A range of traditional and contemporary spectroscopic methods for measuring across different phases is highlighted in an attempt to present a 'detection landscape' for CAP-borne radicals.

Spectral Methods of Control of Impurities, Their Flows and Localization in an Equilibrium Low-Temperature Plasma of Low Pressure

“…The latter, however, violates not only the simplicity but also another important advantage of emission methods, lack of contact, which greatly narrows the scope of their application as independent ones. It is stated in a recent very detailed and useful review of plasma radical spectroscopy [33], e.g., that the emission methods cannot be considered as quantitative ones. We can only partially agree with this, bearing in mind the reservations made above.…”

“…As to the ideology, this group is intermediate between the two previous ones. A compromise is most often used when measuring particle concentrations starting with [112] for the gas analysis and as applied to plasma studies (e.g., reviews [30,31,33]).…”

“…The studies are underway to measure the concentrations of paramagnetic particles (О 2 , ОН, NO, HO 2 …) from the difference between the rotation angles of the s-and p-polarizations of radiation in the resonant cells under the application of the magnetic field [115][116][117]. According to the estimates made in the review [33], in the future such a method can provide the sensitivity of polarization measurements in the magnetic field of ~10-1000 G, e.g., [НО 2 ] radicals ~10 7 cm -3 , while the measurements carried out by traditional CRDS methods and its "off-axis ICOS" version showed the sensitivity of ~[НО 2 ] ~ 10 10 cm -3 [117]. In this case, it is difficult for now to say how this affects the properties of plasma.…”

“…ciative excitation in the process (31). The lifetime is determined by radiative decay and quenching: (33) where are thermal velocities, N i are concentrations, σ iq are quenching cross sections of ОН(A 2 Σ), the subscript i refers to the kind of the gas particles. The Einstein coefficient ~ 3 × 10 6 s -1 , quenching rate constants at (300, 450) K are given in Table 5.…”

“…The studies in order to optimize the technology are carried out directly on them. A number of reviews are devoted to new diagnostic methods, including laser applications [30][31][32][33].…”