Polarization effects in ionizing thermal energy collisions of laser-excited Ne(3p 3 D 3) atoms with Ar atoms

Abstract

Using transverse and longitudinal excitation of a collimated metastable Ne(3s 3P2.o) beam with average velocities of 500, 800, and 1,200 m/s by means of a single mode dye laser on the 2~ 3P2~3 p 3D3) transition, we have investigated ionizing collisions of polarized Ne(3s 3p2) and Ne(3p 3D3) atoms with Ar atoms. The product electrons were energy analyzed with high resolution (9-25meV). The resulting Ne(3p 3D3) electron spectra exhibit a strong dependence on the three types of laser polarization (7~11,7~• chosen to prepare the excited atoms. In contrast, the Ne(3s 3P2) spectra are only weakly dependent on polarization. Detailed model calculations have been carried out for the Ne(3p)+ Ar cross sections, using computed excited-state potential curves, semi-empirical ionic potentials, and local autoionization width functions. A semiclassical closecoupling method is applied to describe the evolution of the polarized collision system in the coupled entrance channels. It is found that a single autoionization width F(R) is not sufficient to describe the measured polarization effects properly. The dependence of F on the initial and final state is expressed in terms of few reduced electronic transition matrix elements, which are determined by comparison of measured and calculated total cross sections and Ar+(2p3/2)/Ar+(2P1/2) branching ratios for ionizing collisions of the various Ne(3p J = 1, 2, 3) multiplet states with Ar. The matrix elements corresponding to Ar(3p a)~Ne(2pa) electron transfer during autoionization are found to dominate, but Ar(3pr0-*Ne(2prc) transfer has also to be included. The resulting calculated electron spectra reproduce the measured polarization effects in a semi-quantitative way.

Detailed electron spectrometric study of the ionization of H2 by He* (21 S, 23 S)

“…The low background in our spectra, achieved by careful collimation of the metastable beam and proper design of the reaction region [9,[35][36][37][38] in conjunction with the use of two stage condensers for electron energy analysis [35][36][37][38][39], rules out the presence of a significant broad continuum of Penning electrons, as reported and discussed by Tuffin et al [-14]. …”

“…The present experiments were carried out with two similar apparatuses, described before in detail [35][36][37][38]. We only give a brief explanation here, pointing out the basic method and the differences between the two setups.…”

“…Apparatus II is similar in its principle design [37,38]. The projectile fluxes are somewhat lower as a result of a 50% better collimation.…”

Polarization and collision velocity dependence of associative ionization in cold Na(3p)-Na(3p) collisions

“…The total signal coming from the experiment is: The main point of confusion enters here: Although gr~l is the mean relative velocity, it is certainly not the mean collision velocity ~7c! This ~5c has to be computed using (14):…”

“…More recently, many of these and similar studies have been performed with atomic beams, a more sophisticated medium in the sense that it enables variations in collision velocity and/or atomic polarization [12][13][14][15][16][17][18][19][20][21][22]. In fact, both parameters can be varied very accurately in a beam, thereby giving the possibility to study the process in great detail.…”