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Deuterium and lithium are light elements of high cosmological andastrophysical importance. In this work we report the first detection ofdeuterated molecules and a search for lithium hydride, 7LiH, at redshift z=0.89in the spiral galaxy intercepting the line of sight to the quasar PKS1830-211.We used ALMA to observe several submillimeter lines of ND, NH2D, and HDO, andtheir related isotopomers NH2, NH3, and H2^18O, in absorption against thesouthwest image of the quasar, allowing us to derive XD/XH abundance ratios.The absorption spectra mainly consist of two distinct narrow velocitycomponents for which we find remarkable differences. One velocity componentshows XD/XH abundances that is about 10 times larger than the primordialelemental D/H ratio, and no variability of the absorption profile during thetime span of our observations. [...] The second component has XD/XH abundancesthat are 100 times larger than the primordial D/H ratio, a deepening of theabsorption by a factor of two within a few months, and a rich chemicalcomposition, with relative enhancements of N2H+, CH3OH, SO2, and complexorganic molecules. We therefore speculate that this component is associatedwith the analog of a Galactic dark cloud, while the first component is likelymore diffuse. Our search for the 7LiH (1--0) line was unsuccessful and wederive an upper limit 7LiH/H2 = 4 x 10^-13 (3sigma) in the z=0.89 absorbertoward PKS1830-211. Besides, with ALMA archival data, we could not confirm theprevious tentative detections of this line in the z=0.68 absorber towardB0218+357; we derive an upper limit 7LiH/H2 = 5 x 10^-11 (3sigma), althoughthis is less constraining than our limit toward PKS1830-211. We conclude that,as in the Milky Way, only a tiny fraction of lithium nuclei are possibly boundin LiH in these absorbers at intermediate redshift.

Detection of deuterated molecules, but not of lithium hydride, in the z=0.89 absorber toward PKS1830-211