Changes in the reactivity of Li toward gas-phase propylene carbonate (PC) induced by the presence of a small amount of Li oxide or Li carbonate as a Li surface impurity have been examined in ultrahigh vacuum by infrared (IR) reflection absorption spectroscopy. Whereas the presence of Li2O simply attenuates the intensity of IR features characteristic of the corresponding alkoxide found upon exposure of clean Li to PC, small quantities of Li2CO3 on Li led to the formation of detectable amounts of the Li alkyl carbonate derivative. Implications of these results to the interpretation of data obtained in situ for Li electrodes in electrochemical environments are discussed. (C) 2002 The Electrochemical Society.