State-selective study of Ar²⁺, Ar³⁺and N₂²⁺formation by electron impact ionization near threshold

Abstract

The M o l d behaviour of eledmn impact ionization of argon atoms and nitrogen molecules is investigated state selectively using the vanstational energy sptromeby (ms) method. A power law of the form # ( E d ) a (Ee, -E d " can be fitted to the measured ionization fnnctions. For double ionization of Ar and Nz we found good agreement with the theoretical predictions based on the Wannier theory for the electron triple escape process. Coefficients for the triple ionization of Ar are closer to those predicted by a swistical model.

Multiple ionization of helium and krypton by electron impact close to threshold: appearance energies and Wannier exponents

“…Some studies confirmed the Wannier exponent of 1.127, some did not [15,16,30]. Prior to our recent paper [8], only Wiesemann and co-workers [31][32][33][34] had attempted to generate systematically reliable experimental data for the threshold law and the AEs for the formation of singly and multiply charged rare gas ions. The exponents reported by us [8] and by Wiesemann and co-workers [31][32][33][34] did in general not confirm the predictions of the generalized Wannier law or the simple nth power law, in particular for n-values larger than 2.…”

“…Prior to our recent paper [8], only Wiesemann and co-workers [31][32][33][34] had attempted to generate systematically reliable experimental data for the threshold law and the AEs for the formation of singly and multiply charged rare gas ions. The exponents reported by us [8] and by Wiesemann and co-workers [31][32][33][34] did in general not confirm the predictions of the generalized Wannier law or the simple nth power law, in particular for n-values larger than 2. However, we note that Wiesemann and co-workers found in some cases (Ar and Kr) good agreement between their measured exponents and predictions from a simple statistical approach introduced by Lebius et al [32,33] which was based on Russek's statistical energy deposition model [36] yielding κ-values well below n for the ionization of these heavier manyelectron atoms up to triple and quadruple charge states.…”

Electron impact multiple ionization of neon, argon and xenon atoms close to threshold: appearance energies and Wannier exponents

“…Despite the interest from the theoretical point of view most high-resolution experiments were concerned primarily with the threshold law for single ionization and, while some confirmed the Wannier exponent of 1.127, some did not (see the discussion in [33] and [15,16]). To the authors' knowledge, there is only one, rather recent, serious effort by Wiesemann and coworkers [34][35][36][37] to generate reliable experimental data for the threshold law and the AEs for rare gas atoms (apart from some older papers, see the discussion below and one study concerning triple photoionization of atomic oxygen and neon [38]). These authors measured systematically (in some of the cases even state selected) the cross sections close to threshold for the formation of He + , He 2+ , Ne + -Ne 4+ , Ar 2+ , Ar 3+ , Kr 2+ , Kr 3+ and Xe 2+ -Xe 4+ following single-electron impact on the respective neutral atoms.…”

“…In order to shed more light onto the discrepancy between experimental data and theoretical predictions we carried out experiments which extended the previous studies in several respects. We have extended the range of ionization charge state up to n = 8 (e.g., for Xe) and employed recently constructed high-resolution electron impact ionization apparatus [7] combining a commercial quadrupole mass spectrometer with a home-built hemispherical electron monochromator which has a much higher energy resolution (up to a factor of ten in the best case [7]) compared to the 500 meV energy resolution used by Wiesemann and coworkers [34][35][36][37]). We also developed new ways to calibrate the electron energy scale and verify its linearity over a wide range of impact energies [41].…”

Doppler-free kinetic energy release spectrum of

“…Regarding N 2+ 2 the experimental and theoretical results are even more comprehensive since this molecule exhibits several optically active electronic states. Photofragment spectroscopy has been used frequently (Cosby et al 1983, Masters and Sarre 1990, Szaflarski et al 1991, Mullin et al 1992, Larsson et al 1992, Sundström et al 1994, Martin et al 1994, but also optical spectroscopy (Carroll 1958, 1991, Auger spectroscopy (Moddeman et al 1971, Svensson et al 1992, kinetic energy release spectroscopy (KER) (Boyer et al 1989, Yousif et al 1990, Ma et al 1991, Vancura and Kostroun 1994, Cho and Park 1995, photoion-photoion coincidence spectroscopy (PIPICO) (Besnard et al 1988), photoion-photon of fluorescence coincidence spectroscopy (PIFCO) (Hellner et al 1988), translational energy spectroscopy (TES) (Hamdan 0953-4075/96/081489+11$19.50 c 1996IOP Publishing Ltd 1489and Brenton 1989, Koslowski et al 1991, Gerdom et al 1994, high-frequency deflection spectroscopy (HFD) (Olsson et al 1988), double-zero kinetic energy spectroscopy (double ZEKE) (Krässig and Schmidt 1992) and threshold photoelectrons coincidence spectroscopy (TPEsCO) (Hall et al 1992, Dawber et al 1994. The spectral resolution varies significantly between these experimental methods.…”