Cumulative contributions of 3s–np (n⩾3) transitions in comparing O atom densities in low-pressure Ar–O2 and He–O2 glow discharges

Many-fold enhancements in the population densities of O atoms in low-pressure glow discharges in Ar–O2 and He–O2 compared with the discharge in pure O2 have been reported in recent years. In some reports, the 3sS3,5–3pP3,5 transitions of O atoms around 844.6 or 777.2nm are considered in estimating the density of atomic oxygen. The authors’ results demonstrate that the contributions of other possible transitions such as 3sS3,5–npP3,5 (n>3) directly feeding the lower 3sS3,5 levels are also significant and should be included for a better estimate of O atom densities.