Measurement of absolute electron-impact excitation cross sections in Ar and N₂ using H and H₂ emissions as secondary standards

Abstract

A detailed description is given of a technique in which emissions from H and H2 are used to calibrate an apparatus used for electron-impact emission cross-section measurements in the wavelength range 90–130 nm. Absolute emission cross sections have been measured at 200 eV electron-impact energy for the 120 nm N I line following dissociative excitation of N2 and for the Ar and Ar+ lines at 104.8, 106.7, 92.0, and 93.8 nm respectively. Good agreement with earlier works is obtained in the case of the N I line when earlier data are renormalized to take into account the recent revision of the cross section for production of Lyman α from H2. Measurements of the 104.8 and 106.7 nm lines suggest a 40% cascade component for the latter line at energies of 200 eV and above.

Photoemission Cross Sections for Atomic Transitions in the Extreme Ultraviolet due to Electron Collisions with Atoms and Molecules

“…When transitions of the H 2 (B l:I;; -X l:It) Lyman band system and other Rydberg band systems are included, a model spectrum for relative calibration between 80 and 165 nm can be generated (Ajello et al 1984(Ajello et al , 1988, based on published values for the transition probabilities, oscillator strengths, Franck-Condon factors, and excitation cross sections. This method is used by Ajello and co-workers (in combination with the double monochromator technique to extend the calibration down to 40 nm, see Ajello et al 1984) (Forand et al 1986, and in combination with other Rydberg band systems by Forand et al 1988) to measure cross sections in SF 6 , Ar, and N 2 ; by Mentall and Morgan (Mentall and Morgan 1974) tu IH<::a~ure cross sections in H 2 0, NH 3 , and CH 4 ; and by Zipf and coworkers (Zipf et al 1979) to measure cross sections in O 2 and CH 4 • Specific vibrational and rotational levels of the H 2 (B l:I u -X l:It) and HD(B l:I u -X l:It) Lyman band systems can be excited by absorption of Ar I ( 106.7 nm) resonance radiation (Becker et al 1971) resulting in a clear spectrum of28 well-separated lines that can be used for relative calibration between 106 and 171 nm. These lines are used by Zipf and co-workers (in combination with the N2 LBH bands, see Stone and Zipf 1972a) to measure cross sections in NO, N, and 0.…”

Measurements of electron impact optical excitation functions

“…A Bethe-Fano plot of their data for the 92.0-nm line has a reasonable intercept, but rather strange behavior above 1 keV. Forand et al (1988) have measured the excitation cross sections for each of these lines at the single energy of 200 eV and find good agreement with these values. The intensity calibration of this measurement was made in terms of Born approximation cross sections for the Lyman series of hydrogen.…”

Cross Sections and Reaction Rates of Relevance to Aeronomy

“…Forand et al [1988] measured the cross section for production of the 1200 Å emission of N by impact of 200 eV electrons on N 2 . Ajello and coworkers presented cross sections for emissions of N 2 and N resulting from electron impact on N 2 obtained in a cross‐beam experiment, including emission from the and states of N 2 [Ajello et al,* 1989a], the 748 Å emission of N + [Tripp et al,* 1990], and the Birge‐Hopfield I Band system [James et al,* 1990].…”

“…Elastic and total scattering cross sections include: Nahar and Wadehra* [1987] (calculation), Subramanian and Kumar [1987] (measurement), Zecca et al [1987] (measurement), and Furst et al* [1989] (measurement). Excitation and emission cross sections and oscillator strengths include: Bartschat and Madison* [1987] (calculation), Li et al [1988a] (measurement), Li et al [1988b] (measurement), Forand et al [1988] (measurement), and Ajello et al* [1990] (measurement). Ionization cross sections include: Avaldi et al, [1989a] (measurement), Avaldi et al [1989b] (measurement), Sánchez et al [1990] (measurement), and Charlton et al [1989] (measurement).…”