Search for Interstellar LiH in the Milky Way

We report the results of a sensitive search for the 443.952902 GHz transition of the lithium hydride (LiH) molecule toward two interstellar clouds in the Milky Way, W49N and Sgr B2 (Main), that has been carried out using the Atacama Pathfinder Experiment telescope. The results obtained toward W49N place an upper limit of on the LiH abundance, , in a foreground, diffuse molecular cloud along the sight line to W49N, corresponding to 0.5% of the solar system lithium abundance. Those obtained toward Sgr B2 (Main) place an abundance limit in the dense gas within the Sgr B2 cloud itself. These limits are considerably smaller that those implied by the tentative detection of LiH reported previously for the z = 0.685 absorber toward B0218+357.