  The line of sight toward Sk 143 (AzV 456), an O9.5 Ib star in the Small
Magellanic Cloud (SMC), shows significant absorption from neutral atoms and
molecules. We report a new study of this line of sight by means of
high-resolution spectra obtained with the ESPRESSO spectrograph at the VLT of
ESO. The absorption from neutral and ionized species is well characterized by a
single component at vhel about +132 km/s that was modeled with the ASTROCOOK
code. The rubidium Rb I 780.0 nm line is detected for the first time outside
the Galaxy, and we derive [Rb/H]= -1.86 +/- 0.09. As a result of the high
resolution, the 85Rb and 87Rb isotope lines are also exceptionally well
resolved. The 85Rb/87Rb isotope ratio is 0.46, which is opposite of the
meteoritic value of 2.43. This implies that Rb is made through a dominant
contribution of the r-process, which is dominant for the 87Rb isotope. We also
confirm the presence of 7LiI 670.7 nm and set a limit on the isotopic ratio of
6Li/7Li < 0.1.The dominance of the 87Rb isotope implies that Rb is made through
a dominant contribution of the r-process. At the low metallicity of the cloud
of [Zn/H] = -1.28 +/- 0.09 , neutron rich material may have occurred in
rotating metal-poor massive stars. Moreover, the low metallicity of the cloud
leads to an absolute Li abundance of A(7Li) about 2.2, which differs from the
expectation from big bang nucleosynthesis. Because the gas-phase abundance is
not affected by stellar depletion, the burning of Li inside the halo stars is
probably not the solution for the cosmological 7Li problem.
