L ? emission from Ar++H2 collisions in the threshold energy region

Abstract

In the energy range 2.4 to 33.3 eVcra, relative cross sections have been measured for L~ emission from impact of Ar § ions in a beam on a H 2 gas target. Absolute cross sections, obtained by normalization to literature data, are 1-10 x 10 -16 cm 2 for metastable Ar § and 1-20x10-18cm 2 for ground state Ar § In the former case, the dominant mechanism is probably dissociative electronic energy transfer, while in the latter case dissociative charge transfer is the most likely process. In addition,~at the lowest energies L~ resulting from a chemiluminescent rearrangement Ar++ H 2--, ArH + +H(2p) has been observed.

L ? emission from collisional excitation of H Atoms by threshold energy Ar+ ions

“…4. Figure 4 also shows the cross section for undischarged H 2 [22] as a solid line. At each ion energy, data were taken alternately with the discharge on and off, each with photon count accumulation for 1 h. For many energies, several such runs were averaged.…”

“…4 has been calibrated by measurements of L~ from H++ Ar, for which the cross section is known from a careful absolute determination by Suchannek and Sheridan [17]. Also as in [22], the ion source cathode-toanode voltage, UA, was kept in all experiments at U A --25-28V, i.e. well below the appearance potential of metastable Ar § which is 32V [30,31].…”

“…H(2s) atoms can be quenched by comparatively weak electric fields (see, e.g., [11,12]); however, with the ion draw-out field of ~ 1 V/cm applied in the collision region the H(2s) lifetime is in the ms range [29], much longer than the residence time of the collision products in the observation region. As in [22], the ordinate scale of Fig. 4 has been calibrated by measurements of L~ from H++ Ar, for which the cross section is known from a careful absolute determination by Suchannek and Sheridan [17].…”

“…The apparatus is the same as that used in our recent measurements of L, emission from Ar + +H 2 collisions [22]. It incorporates a mass-selected ion beam, a target gas chamber and an optical spectrometer (resolution 26• FWHM) with photon counting electronics.…”

“…It incorporates a mass-selected ion beam, a target gas chamber and an optical spectrometer (resolution 26• FWHM) with photon counting electronics. The original apparatus [23,24] was modified slightly as described in [22]. For the present work, the most important modification was the addition of a microwave discharge and the use of a teflon collision chamber, see Fig.…”