The vibrational properties of vapor-deposited lithium films exposed to propylene carbonate (PC) vapors at room temperature have been examined by infrared reflection-absorption spectroscopy (IRAS) in ultrahigh vacuum (UHV) using a specially designed chamber. The sharply defined spectral features observed were found to be incompatible with those of either, lithium propoxide, lithium alkyl carbonate, lithium carbonate, or mixtures thereof. Instead, the IRAS spectrum of PC/Li/Ni was found to be identical to that obtained by exposing Li to 1,2-propanediol vapors under otherwise identical conditions and may thus be attributed to the corresponding alkoxide derivative.