Electronic ground state OH(X) radical in a low-temperature atmospheric pressure plasma jet

Abstract

The wide applicability of atmospheric pressure plasma jets in biomedicine stems from the presence of reactive nitrogen and oxygen species generated in these plasma jets. Knowing the absolute concentration of these reactive species is of utmost importance as it is critical, along with the particle flux obtained from the plasma feed gas flow rate to ensure that the correct dosage is applied during applications. In this study, we investigate and report the ground state OH(X) number density acquired using cavity ringdown spectroscopy, along the propagation axis (z-axis) of a cold atmospheric pressure helium plasma plume. The jet was generated by a repetitively pulsed mono-polar square wave of duration 1 μs running at a frequency of 9.9 kHz. The voltage supplied was 6.5 kV with the helium flow rate fixed at 3.6 standard liters per minute. The rotational and vibrational temperatures are simulated from the second positive system of nitrogen, N2(C3πu−B3πg), with the rotational temperature being spatially constant at 300 K along the propagation axis of the atmospheric pressure plasma jet while the vibrational temperature is 3620 K at the beginning of the plume and is observed to decrease downstream. The OH(A) emission intensity obtained via optical emission spectroscopy was observed to decrease downstream of the plasma jet. The OH(X) number density along the propagation axis was initially 2.2 × 1013 molecules cm−3 before increasing to a peak value of 2.4 × 1013 molecules cm−3, from which the number density was observed to decrease to 2.2 × 1013 molecules cm−3 downstream of the plasma jet. The total OH(A, X) in the plasma jet remained relatively constant along the propagation axis of the plasma jet before falling off at the tip of the jet. The increase in vibrational temperature downstream and the simultaneous measurements of both the excited state OH(A) and the ground state OH(X) reported in this study provide insights into the formation and consumption of this reactive oxygen species while also providing a reference for determining the radical number density dosage for future cold plasma irradiation studies.

A KHz frequency cold atmospheric pressure argon plasma jet for the emission of O(1S) auroral lines in ambient air

“…In all cases, the entire plasma plume is always dominated by the 557.7 nm emission regardless of argon flow rate and electrode gap albeit the overall plasma characteristics show dependence on the operating parameters. The plasma jet is found to be more sensitive to the gas flow rate as reflected from the photographs which is similar to previous work 19 . However at relatively larger electrode gap (above 40 mm) a filament is formed in the middle of the plume with purple color visible at the tip as pointed out by the arrow in Fig.…”

Characterization of dielectric barrier discharges with water in correlation to productions of OH and H2O2 in gas and liquid phases

“…Therefore, the quantitative measurements of OH radicals have been performed in gas phase using, e.g., laser-induced fluorescence (LIF) spectroscopy, 7,[19][20][21]25,[27][28][29][33][34][35][36][37]39) absorption spectroscopy with broadband UV-LED, 6,26,46,47) and cavity ringdown spectroscopy. 62,63) In liquid phase, chemical methods with OH trapping or scavenging reagents are used. 23,41,43,48,53) On the other hand, the energy yield of H 2 O 2 production has also been investigated by using various types of reactors as described above, and summarized in literatures up to present.…”

Characteristics of differentiation of osteoclast cells irradiated with active species in atmospheric oxygen plasma

“…On the other hand, there have been some reports on the observation of OH(X) in the gas phase on the water surface. 28,29) In this experiment, direct generation of ground-state OH(X) from H 2 O can occur in the plasma. 24,30) Also there is a possibility that some small portion of OH(A) can be deexcited into OH (X) in the gas phase, even though fluorescent light emission with a wavelength of 309 nm has not been observed.…”