Differential measurements of metastable Ne(2p⁵3s³P_0,2) on Ne(2p⁶¹S₀) collisions at thermal energies

An adjustment of the Ne*2(3P0,2-1S 0) potentials to thermal-energy scattering data

“…Up to now, the method providing the highest angular and energetic resolutions, consists in crossing two supersonic beams of neon, metastable atoms being produced within one of them by a collinear electronic bombardment [9][10]. We have developed a simpler, but less performing technique, using two effusive beams of neon : by means of a synchronous chopping of these beams, combined with a time of flight measurement, it is possible to select the relative velocity [11]. Moreover, by detecting metastable atoms scattered in the direction perpendicular to the initial velocity plane, where neither elastic nor endothermic processes can be detected, we have observed the exothermic fine structure transition :…”

Differential measurements of metastable Ar(3p5 4s, 3P 0,2) on Ar(3p6, 1S0) collisions at thermal energies

“…2). It may be already seen on curve A, obtained with a limited angular resolution (LB6L ~ 3.2~), that the Ar*-Ar differential cross-section is very different from that of the Ne*-Ne collision at 78 meV [3] (curve C) : it is strongly peaked at Fig. 2.…”

“…The angular dependence of the scattered intensity and the velocity dependence of the differential cross-section in the backward scattering direction are given. Differential cross-sections in metastable Ne on Ne collisions at thermal energies have recently been measured in supersonic [ 1,2] or effusive [3,4] crossed beam experiments. These measurements are a stringent test of the validity of the calculated Ne!…”

“…The experimental set-up shown in figure 1 is an adaptation of that described previously [3], where the effusive ground-state atom beam is replaced by a Campargue type supersonic beam. The main advantage of this beam is to be quasi-monokinetic (A~/r ~ 3 %).…”

“…The number N(0~ t) of metastable atoms detected at an angle OL and after a time-of-flight t is proportional to : where duldwL is the differential cross-section in the laboratory frame (averaged over the angular spread L1(JL), Vr is the relative velocity, S (t 1) is the square gate function of the metastable atoms, f(TI/11) is the T.O.F. distribution [3] over the distance It between the metastable atom source and f the collision volume, and Ti tll -, t 1 -ll where ~1,~1 are respectively the velocities of the vi 1 VI metastable atoms before and after the collision, ii is the distance between the collision volume and the detector.…”