Spectroscopic diagnosis and global modeling of low-power atmospheric-pressure Ar/CF₄ microwave plasma jets

Atmospheric-pressure Ar/CF₄ microwave plasma jets are vital for precision optical fabrication and surface fluorination. However, spectroscopic characterization of their reactive fluorocarbon species remains challenging. Here, we present a combined experimental and computational study on a low-power (≤10 W) Ar/CF₄ microwave plasma jet. High-resolution optical emission spectroscopy is employed to resolve the rovibrational structures of key molecular emitters, including the C₂ Swan bands (d³Π_g-a³Π_u) and the OH (A²Σ-X²Π) band. From these spectra, the gas temperature (823-2278 K) and effective vibrational temperature (1910-3340 K) are derived via detailed spectral fitting. The electron density is determined independently from Stark broadening of the H_α line. To overcome OES limitations for non-emissive species, a zero-dimensional global model is developed and critically benchmarked against the experimental spectral trends. The model predictions show good qualitative agreement with the experimental trends, suggesting that the electron density reduction with increasing CF₄ is likely dominated by enhanced inelastic collisional losses (raising electron temperature) rather than direct electron attachment, as supported by combined Stark broadening analysis and simulated particle balances. The model further shows a transition in CF₄ dissociation pathways. This work establishes a combined spectroscopic diagnosis and modeling framework, providing a mechanistic understanding of energy transfer and reaction kinetics in fluorocarbon microwave plasmas through quantitative molecular spectroscopy.