Gas-phase diagnostic studies of H2 and CH4 inductively coupled plasmas

Abstract

Determination of molecular temperatures within low-temperature plasmas is critical to understanding the reactions that drive the chemistry of these systems and the mechanisms involved in plasma-surface interactions. Optical emission spectroscopy was employed to investigate gas-phase processes in H2 and CH4 inductively coupled plasma systems. Specifically, rotational temperatures (TR) have been determined for H2 d3Πu→a3Σg+ and CH A2Δ→X2Π under a variety of plasma parameter conditions. In 100% H2 plasmas, TR(H2) values are ∼500–550 K, whereas generally higher TR(H2) values (∼500–700 K) are reported for 100% CH4 plasmas. Disparities in the rotational temperature values and trends of H2 (d3Πu) between H2 and CH4 plasmas highlight the differences in H2 excitation pathways occurring in each of these two plasma systems as TR can be affected by the mechanism for molecule formation and excitation within plasma systems. As such, mixed gas CH4/H2 plasma systems were also explored to gain further insight into these mechanistic details. These results emphasize the connections between fundamental plasma properties and plasma parameters, a key component to understanding and optimizing plasma conditions for the future development of a host of plasma technologies.