Ionization of hydrogen and deuterium atoms in thermal energy collisions with state-selected Ne(3s 3 P 2,3 P 0) metastable atoms

Abstract

High resolution energy spectra of electrons and ions resulting from thermal energy collisions of hydrogen and deuterium atoms with state-selected metastable Ne(3s3P2, 3P0) atoms are reported. The electron spectra for Ne(3P2)+H(D) are very broad: The high energy part due to formation of Nell § (NeD +) bound states (associative ionization), amounts to about 30 % of the ionizing events, whereas the dominant part of the spectrum including a prominent low-energy peak is due to Penning ionization out of a strongly-attractive entrance potential curve. Comparison of the spectra with quantum mechanical fit calculations yields fairly accurate information on this potential, in particular its well depth De[Ne(3p2)-H,D]=2.0(1)eV. The spectra for Ne(3Po)+H,D are comparatively narrow with much lower cross sections than the one for the Ne(3P2) state. The corresponding entrance channel is a weakly bound van der Waals molecule with a well depth below 0.1eV. A perturbation calculation of the Ne(3s)+H(ls) potential energy curves at large distances explains the observed difference between the Ne(3P2)+ H(D) and Ne(3P0)+H(D) systems. Symmetry arguments are given that the major contribution to the Ne(3P2)+H(D) spectra is due to the 22; potential.

The state dependence of the interaction of metastable rare gas atoms Rg*(ms3 P 2,3 P 0) (Rg=Ne, Ar, Kr, Xe) with ground state sodium atoms

“…8) and the most strongly attractive Rg* (ms 3P2) + Na(3 s) potential (curve "a"), which has 2S~/2 character at smaller R, are found. Within the electron exchange model for Penning ionization [30,31], one expects the latter potential to be the major contributor to ionization in Rg*(ms 3Pz)+Na(3s ) collisions, as discussed previously for Ne*(3s 3P2)+H, Li, Na, K [6,7]. Its calculated potential well depth D*(a) reaches about 94% of the well depth D~e for the singlet potential (see Table 4).…”

“…The 3Pz electron spectra are very similar for all four systems: they are dominated by a peak at electron energies Ep<Eo, typical for a system having an attractive excited state potential V*(R) corresponding to well depths of several tenths of an eV [1,7,8]. A secondary Airy-type maximum [3,[5][6][7][8][9][10][11][12][13] is observed, which gradually disappears from Ne* to Xe*; this behaviour reflects the combined effects of the decrease in the well depths and the increase in the reduced mass and in the number of contributing partial waves, when going from Ne* to Xe*. The high energy tail of the spectra (E > Eo), most clearly seen in the Xe data, is due to ionization at closer R range and reflects, in part, the attraction of the Rg + N a + exit channel potential.…”

“…High resolution energy analysis of electrons resulting from ionizing thermal energy collisions of electronically excited atoms with atoms and molecules (Penning ionization) yields detailed information about the molecular interactions [1][2][3][4][5][6][7][8][9][10][11][12]. For most of these studies, metastable * Dedicated to Prof. Dr. J.P. Toennies on the occasion of his 60th birthday He*(23S, 21S) atoms have been used because of their high excitation energies (~20 eV), long lifetimes, ease of production and state selection, importance in discharges, and theoretical simplicity.…”

“…For most of these studies, metastable * Dedicated to Prof. Dr. J.P. Toennies on the occasion of his 60th birthday He*(23S, 21S) atoms have been used because of their high excitation energies (~20 eV), long lifetimes, ease of production and state selection, importance in discharges, and theoretical simplicity. The investigation of (quasi) one electron target atoms (/-/, D; alkali atoms A) is particularly important in connection with a thorough test of the theoretical description of the Penning process [5][6][7][8][10][11][12][13][14]. Our group has recently reported detailed experimental studies of the electron spectra for He*(23S, 21S)+H, A [8, i0, tl, 13] along with quantum mechanical analyses [10,11,13] of part of the data, based on ab initio potentials [10,11,13,14].…”

“…In contrast, the He* (21S) interaction with X is less strong [8,11,13,14], but still appreciable (well depths 0.2-0.45 eV). In a continuing effort, to also characterize the interactions of the heavier metastable rare gas atoms Rg*((m--1)pS ms 3P2, 3P0) with a variety of other atoms [6,7,15], we have now investigated the systems Rg*(ms 3Pz, 3Po)+Na(3s ) (Rg=Ne, Ar, Kr, Xe; m= [3][4][5][6]. It is our aim to elucidate systematic trends in the behaviour of the different heavier metastable atoms interacting with a selected target atom X. Lorenzen et al [6,73 have previously observed an interesting, strongly different behaviour of Ne*(3s 3P2) and Ne*(3s 3p0) atoms in their interactions with X = H , D, Li, Na, K: the total ionization cross sections and potential well depths for Ne*(3p2)+X are much larger then those for Ne* (3Po) + X.…”