Search for LiH in the ISM towards B0218+357

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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 10¹² cm⁻² for an assumed excitation temperature of 15 K, or a relative abundance LiH/H₂ 3 10⁻¹². We discuss the implications of this result.