Eur. Phys. J. D 54, 77-86 (2009)
https://doi.org/10.1140/epjd/e2009-00174-9

A study of OH radicals in an atmospheric AC discharge plasma using near infrared diode laser cavity ringdown spectroscopy combined with optical emission spectroscopy

¹ Department of Physics and Astronomy, and Institute for Clean Energy Technology, Mississippi State University, Starkville, MS, 39759, USA
² Department of Chemistry, State University of New York College of Environmental Science and Forestry, Syracuse, NY, 13210, USA

Corresponding author: ^a cw175@msstate.edu

Received: 18 March 2009
Revised: 30 April 2009
Published online: 16 June 2009

Abstract

Simultaneous measurements of absolute concentrations of H₂O and OH radicals in an atmospheric AC discharge using continuous wave cavity ringdown spectroscopy (cw-CRDS) are reported. Formation of OH radicals and plasma temperatures are characterized by optical emission spectroscopy. The concentration of OH radical at the edge of the discharge plume at 380 K is measured by the cw-CRDS technique to be 1.1 ×10¹⁵ molecule cm^-3. Ringdown measurements of the H₂O (120-000) band and the OH first overtone around 1515 nm enable us to determine an OH generation yield, , to be 4.8 ×10^-3, where N_OH and are the number densities of OH and H₂O, respectively. The minimum detectable absorption coefficient of the cw-CRDS system is 8.9 ×10^-9  cm^-1, which corresponds to a 1σ detection limit of OH number density of 1.2 ×10¹³ molecule cm^-3 in the discharge. This experimental approach is demonstrated for the first time ever in an AC discharge, and can be applied in general to a variety of atmospheric plasmas to help study OH formation mechanisms and OH-related plasma applications.