Measurement of C2 and CH temperatures in argon‐acetylene low‐pressure microwave‐induced plasma

Abstract

The emission spectra of C2(d3Πg–a3Πu), CH(A2Δ–X2Π), and CH(B2Σ–X2Π) bands are analysed to measure rotational Trot, vibrational Tvib, and gas temperature Tg from Ar/C2H2 (5–20% C2H2) microwave‐induced plasma (MIP). In case when helium and hydrogen are used in the gas mixture instead of argon, no significant change in Trot is noticed. Both studied temperatures are insensitive in terms of the C2H2 percentage. From CH(0–0, A2Δ–X2Π) band R2 branch lines, two Trot (Trot ∼ 520–580 K for J′ = 3–9 and Trot ∼ 1,700–1,800 K for J′ = 10–17) are determined. The lower Trot equals the Tg (500–700 K) measured from C2 bands in this study. The H2 Fulcher‐α diagonal bands are recorded as well in the H2/C2H2 mixtures and Trot∼750–900 K of the H2 ground state measured. Tvib ∼ 6,000 K in Ar/C2H2 MIP is calculated from the integral intensity ratio of C2(2,1) and C2(3,2) bands.