Étude par pompage optique de l'échange de métastabilité dans le néon

Abstract

2014 Nous mettons en évidence les collisions d'échange de métastabilité dans le néon entre atomes dans l'état métastable Ne*(3P2) et dans l'état fondamental. Pour cela nous créons par pompage optique une orientation des atomes Ne* portés dans l'état métastable par une décharge dans du néon sous faible pression.Nous mesurons le taux de relaxation des Ne* par l'élargissement des courbes de résonance magnétique en fonction de la pression de néon. Les expériences portent sur des mélanges isotopiques comportant des proportions variables d'isotopes pairs et de 21Ne. Après un calcul des transferts d'orientation électronique et nucléaire au cours des collisions Ne*-Ne, nous déduisons des mesures d'élargissement une valeur de la section efficace d'échange de métastabilité dans le néon à 300 K : 03C3e = (22 ± 6) 10-16 cm2. Cette valeur est compatible avec des calculs récents effectués à partir de déterminations ab-initio des potentiels moléculaires de Ne2.Abstract. 2014 We study metastability exchange collisions in neon between metastable Ne*(3P2) atoms and Ne ground state atoms. The metastable atoms are created by a weak discharge in neon at low pressure and oriented by optical pumping. We measure the pressure broadening of the Ne* magnetic resonance curves which gives the collisional relaxation rate. The experiments are performed with isotopic mixtures containing different proportions of even isotopes and 21Ne. We calculate the transfer of electronic and nuclear orientation in Ne*-Ne collisions. From the pressure broadening measurements we deduce the metastability exchange cross-section in neon at 300 K : 03C3e = (22 ± 6) 10-16 cm2. This value is in reasonable agreement with recent predictions based on ab-initio calculations of the Ne2 molecular potentials. LE JOURNAL DE PHYSIQUE TOME 38, JUIN 1977, Classification Physics Abstracts 5.2801. Introduction. -Les collisions atomiques qui se produisent dans les gaz soumis a des d6charges ont fait d6jA l'objet de tr6s nombreuses 6tudes. Des esp6ces tr6s vari6es sont pr6sentes dans les d6charges :

Velocity selective optical pumping

“…Moreover, (6) Comparing the areas of the backgrounds (normalized with the peak areas) for the alignment and orientation signals, respectively, gives (1 -ç(2»)/(1ç(1») ~ 1.5. This rough estimate is in agreement with measurements in optical pumping [23].…”

“…This is an interesting situation since the quasi perfect conservation of nuclear orientation during atomic collisions would completely destroy any correlation between internal and external variables of the atoms, and therefore wipe out any Doppler-free peak, if the effect of metastability exchange collisions were negligible. Simply speaking, the metastability exchange collisions with unpolarized ground state Ne atoms act as a relaxation process and restore the line shape of the form (23). In principle, the dependence of exchange cross-sections on velocity change could be studied in this way.…”

The role of the Pauli principle in metastability exchange collisions

“…The proportionality coefficient is nothing but the probability that no electronic energy transfer will occur during the collision. Equation (10) Equations (12) and (13) where 6;n;t is given by (2). As where AIexch is real.…”

HENSELIAN VALUATIONS OF DIVISION RINGS AND THE GROUPSK1

“…X('S,) is the atomic ground state (configuration 'tp6) and X*(3P2) is the metastable state, also called Is, in the Paschen notation (configuration np5(n + 1)s). This study follows a similar one conducted in neon and described in a more detailed paper (Pinard and Leduc 1977). Such collisions can be studied by differential scattering using beam methods; results have already been reported in the case of Ar (Gillen et al 1976).…”

“…Clearly when writing this equation, we have ignored the interference term between the two processes in the case of two identical isotopes. This approximation is discussed in detail in Pinard and Leduc (1977). One way to get more information about ME and DWE collisions is to study odd isotopes also, making use of their non-zero nuclear spin.…”