ISSN:
1434-601X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract It is shown that relaxation times for the excitation of metastable levels of Ba and Tl by collisons of the ground state atoms with carrier gases Ne and Ar can be measured with good accuracy behind reflected shock waves (2700≦T≦3300 °K) by means of two-channel atomic line absorption spectroscopy. Quenching cross-sections, which thus can be derived, cover in principle the range 10−14 cm2〈Q〈10−21 cm2. In collisions with Ar one finds for the deactivation of Ba(1 D 2)Q=1.2 · 10−19cm2, of Ba(3 D 1)Q=0.95 · 10−19 cm2 and of Tl(2 P 3/2)Q〈5 · 10−21 cm2 without noticeable temperature dependence. From this follows a) (on the basis of the Landau-Zener formula) that the pseudo-crossing of the potential energy curves of Ba-Ar takes place within 0.25 eV of the Ba(D) levels and b) that spin-orbit coupling is not rate controlling in the Ba(3 D 1 →1 S 0) transition. The ratio of cross-sections for quenching of Ba(1 D 2) by Ar and Ne is about 3, suggesting that the polarizabilities of the noble gas collision partners play a major rôle in the transition probabilities. The mean self-quenching cross-sectionQ=5 · 10−16 cm2 of Tl(2 P 3/2) at 3000 °K is about the same as the one reported for 1000 °K and it exceeds the self-quenching cross-section of metastable Ba by at least one order of magnitude.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01392539
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