Atomic oxygen ³P → ³S⁰ (λ1304Å) transition revisited: Cross section near threshold

Abstract

Abstract. The direct excitation cross section for the atomic oxygen 3p ___> 3S0 transition (X1304•) has been measured at four incident energies between 13.4 and 40 eV. These measurements were made to add sufficient detail to previous direct excitation measurements to allow the near-threshold cross section to be determined. Previous optical measurements of the 1304fk emission cross section disagree by up to a factor of 2 in this important energy region. We have also compared the atomic hydrogen e + H(ls) --• H(2s + 2p) cross section, used previously as a secondary standard for our direct excitation measurements of atomic oxygen cross sections, to recent measurements of the total e + H --• Lyman alpha cross section and have found agreement at the _+ 15% level, making a revision of our previously reported atomic oxygen cross sections unnecessary. Previous MeasurementsAny measurement of a cross section for production of excited states of an unstable species such as atomic oxygen is a difficult experimental problem. Not only is it necessary to produce the species in reasonable density, but its abundance must be determined, either absolutely or with reference to another species also present which has an observable transition whose cross section is well enough known to be used as a secondary

Electron Collisional Excitation Rates for O i Using the B ‐Spline R ‐Matrix Approach

“…These lines belong to the 3 P-3p 3 P, 5 P, 3 P-1 D, 3 P-3s 5 S o , 3 S o , 3 P-3d 3 D o , 3 P3s 0 3 D o , 3 P-3s 00 3 P o , and 3 P-2s2p 5 3 P o transitions (where 3s, 3s 0 , and 3s 00 represent 2s 2 2p 3 ð 4 S o Þ, 2s 2 2p 3 ð 2 D o Þ, and 2s 2 2p 3 ð 2 P o Þ cores, respectively). Our calculated excitation cross sections show good agreement with the measured cross sections of Doering and coworkers (Gulcicek & Doering 1987Gulcicek, Doering, & Vaughan 1988;Doering & Yang 2001) and Kanik et al (2001) for the resonance 3 P-3s 3 S o , 3 P-3d 3 D o , and 3 P-3s 00 3 P o transitions and differ significantly for the resonance 3 P-3s 0 3 D o and 3 P-2s2p 5 3 P o , intercombination 3 P-3s 5 S o , and forbidden 3 P-3p 3 P transitions, particularly at higher energies.…”

“…The measured excitation cross sections for the resonance 1027, 989, 878, and 792 Å lines and the intercombination line at 1356 Å are also presented by Doering and coworkers (Vaughan & Doering 1987Gulcicek & Doering 1989;Doering & Gulcicek 1989). The absolute excitation cross sections for the resonance lines at 1304, 1027, 989, and 878 Å are also reported by Kanik et al (2001) at 30, 50, and 100 eV using the electron-energy-loss method with uncertainties similar to the recent measurements of the Doering & Yang (2001). Emission cross sections for the 1304 Å line are measured by Noren et al (2001), while the measured emission cross sections for the lines at 1304, 1027, 989, and 878 Å are presented by Wang & McKonckey (1992), Zipf & Erdman (1985), and Zipf & Kao (1986).…”

“…The chemically unstable and reactive nature of atomic oxygen makes the measurement of absolute excitation cross sections difficult, and the measured cross sections contain rather large uncertainties. The electronenergy-loss measurements of direct absolute excitation cross sections for the 2p 4 3 P-2p 3 3s 3 S o transition have been reported by Doering & Yang (2001), , and with uncertainties in the range from AE20% to AE30%. The measured excitation cross sections for the resonance 1027, 989, 878, and 792 Å lines and the intercombination line at 1356 Å are also presented by Doering and coworkers (Vaughan & Doering 1987Gulcicek & Doering 1989;Doering & Gulcicek 1989).…”

Accurate cross sections for excitation of resonance transitions in atomic oxygen

“…Doering and coworkers measured direct excitation cross sections for several resonance, intercombination, and forbidden transitions using the electron energy loss method. Absolute excitation cross sections of the 2 p 4 3 P –2 p 3 3 s 3 S o transition at 1304 Å have been measured by Doering and Yang [2001], Gulcicek and Doering [1988], Vaughan and Doering [1986, 1987], and Doering and Vaughan [1986]. The latest measurement from this group by Doering and Yang [2001] is quoted to contain an overall uncertainty of ±20% in the cross sections.…”

“…Absolute excitation cross sections of the 2 p 4 3 P –2 p 3 3 s 3 S o transition at 1304 Å have been measured by Doering and Yang [2001], Gulcicek and Doering [1988], Vaughan and Doering [1986, 1987], and Doering and Vaughan [1986]. The latest measurement from this group by Doering and Yang [2001] is quoted to contain an overall uncertainty of ±20% in the cross sections. The excitation cross sections for the resonance 2 p 4 3 P –2 p 3 3 d 3 D o , 2 p 4 3 P –2 p 3 3 s 3 D o , 2 p 4 3 P –2 p 3 3 s 3 P o , and 2 p 4 3 P –2 s 2 p 5 3 P o transitions have been measured by Vaughan and Doering [1987, 1988] and Gulcicek and Doering [1988].…”