Electronegativity of Hollow Cathode DC Discharge in ${\rm O}_{2}$ Employing Electrostatic Probe Diagnostics

Electron temperature and number density are investigated employing hollow cathode dc discharge in ${\rm O}_{2}$. Electron temperature is found to decrease from 3 to 1.85 eV as the pressure increases from 75 to 375 mTorr. Positive and negative ion densities are determined as a function of plasma gas pressure. $I{-}V$ curves are evaluated employing the Allen–Boyd–Reynolds (ABR), current balance, orbital motion limited, and the floating potential (FP) methods. The ABR method is found to yield the highest positive ion number density, whereas the FP method results for $n_{+}$ are extremely small for any meaningful data. Present results are compared to those obtained employing global simulation method as well as with other experimental groups. ${\rm O}_{2}$ electronegativity results are compared with other experimental and theoretical groups. Optical emission spectroscopy is employed and intensity ratio for the 777 and 845-nm lines is obtained for comparison with other groups concluding that ${\rm O}^{-}$ is the dominant species.