Cavity ringdown studies of the E–H transition in an inductively coupled oxygen plasma: comparison of spectroscopic measurements and modelling

Rogers, Samuel D A; Bond, Amelia ORCID: https://orcid.org/0000-0002-9539-6698; Rhodes, Benjamin J; Peverall, Robert; Hancock, Gus; Ritchie, Grant A D. 2022 Cavity ringdown studies of the E–H transition in an inductively coupled oxygen plasma: comparison of spectroscopic measurements and modelling. Plasma Sources Science and Technology, 31 (11), 115006. 16, pp. https://doi.org/10.1088/1361-6595/ac9d62

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Abstract/Summary

The absolute number density of ground state oxygen atoms, O(3P), present in a 100 mTorr oxygen plasma has been determined as a function of operating power using cavity ringdown spectroscopy (CRDS). The dissociation fraction increases by an order of magnitude from ∼0.8% at 50 W to 8% at 250 W and reflects a similar increase in the electron density over this power range. Emission spectra show that the E–H switchover is accompanied by increased rotational heating of O2 and this behaviour is also observed in the translational temperatures determined by fitting the Doppler limited O(3P) CRDS data. The measurements are contextualised via a volume averaged kinetic model that uses the measured absolute densities of O(3P) and O2(a1Δg, v = 0) as a function of power as its benchmarks. Despite the inherent spatial inhomogeneity of the plasma, the volume averaged model, which uses a minimal set of reactions, is able to both reproduce previous measurements on the absolute density of O− and to infer physically reasonable values for both the electron temperature and number density as the E–H switch over is traversed. Time-resolved emission measurements return a value of 0.2 for the wall loss coefficient for O2(b1Σg+); as a consequence, the number density of O2(b1Σg+) is (at least) one order of magnitude less than O2(a1Δg).

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1088/1361-6595/ac9d62
ISSN:	0963-0252
Date made live:	17 Nov 2022 12:13 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/533575

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.1088/1361-6595/ac9d62

ISSN:

0963-0252

Date made live:

17 Nov 2022 12:13 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/533575