Search for LiH in the ISM towards B0218+357

We report a tentative detection with the IRAM 30m telescope of the LiH molecule in absorption in front of the lensed quasar B0218+357. We have searched for the J = 0 -- 1 rotational line of lithium hydride at 444 GHz (redshifted to 263 GHz). The line, if detected, is optically thin, very narrow, and corresponds to a column density of N(LiH) = 1.6 10$^{12}$ cm$^{-2}$ for an assumed excitation temperature of 15 K, or a relative abundance LiH/H$_2 \sim$ 3 10$^{-12}$. We discuss the implications of this result.