Gas-Phase Chemistry in Inductively Coupled Plasmas for NO Removal from Mixed Gas Systems

Abstract

Inductively coupled rf plasmas were used to investigate the removal of NO from a variety of gas mixtures. Laser-induced fluorescence and optical emission spectroscopy were employed to measure the relative gas-phase density of NO as a function of the applied rf power, gas mixture, and catalytic substrate type. In general, the overall density of NO decreases as a function of applied rf power in both NO and N(2)/O(2) plasmas, but the addition of gases such as H(2)O vapor and CH(4), as well as the presence of Au-coated substrates, significantly affects the behavior of NO in these systems. Rotational and vibrational temperatures for NO were measured using laser-induced fluorescence excitation spectra and optical emission spectra. Results show NO vibrational temperatures are about a factor of 5 higher than rotational temperatures and indicate little dependence on applied rf power, feed gas composition, or overall system pressure. Possible mechanisms for the observed changes in [NO] as well as the rotational and vibrational temperature data are addressed.

Using Fundamental Spectroscopy to Elucidate Kinetic and Energetic Mechanisms within Environmentally Relevant Inductively Coupled Plasma Systems

“…In some cases, no specific formation and destruction of species were detected on the time scale of our system, further discussed below. Limitations of OES for reliable species density has been described in detail previously. ,, These include the observations that the actinometer and species of interest must undergo known electron impact excitation processes; be primarily excited from the ground state; optical emission branching ratios of lines of interest and other de-excitation pathways should be constant; and both species must have similar thresholds for the electron impact cross sections …”

Determination of internal temperatures within nitric oxide inductively coupled plasmas

“…Interestingly, T R trends observed in the present work appear to be somewhat different than other previously determined NO internal temperatures within our laboratory . Morgan et al performed LIF studies under a similar parameter space, reporting T R values of ∼350 K, regardless of pressure or power conditions for 100% NO plasmas.…”

“…Examining the excited state data, the 100 and 150 mTorr data are also similar, although the overall trend is a decrease in T V with increasing pressure. Our current work determining T V can again be compared to previous work by Morgan et al, wherein T V was reported for excited state NO species via OES analysis . Note that T R and T V values for the emission and absorbance of NO in 100% NO plasmas are summarized as a function of plasma parameters in the Supplemental Information, Tables S1 and S2, respectively.…”

“…This line of inquiry regarding substrate effects can be furthered compared to the work of Morgan et al In the previous study, T V was determined for excited state NO via OES with Si, Au, and Pt substrates positioned 5 and 12 cm downstream from the coil region . The inclusion of a substrate did not significantly impact T V regardless of substrate type.…”

“…At the center of the most intense fluorescence, “beam only” and “scatter” images are cross‐sectioned (20 pixels wide) along the laser propagation axis. Note that although a single transition for a single rovibrational state was probed in the experiments reported here, we have performed extensive studies across numerous excitation transitions with no significant change in the measured surface scatter coefficient for NO . Thus, the scatter results discussed here are applicable to all NO ground state species.…”