Using high resolution electron energy loss spectroscopy (EELS), we have measured three vibrational bands on a clean CuZn α 75/25 (110) surface after O2 exposure. The band at 420cm-1 is related to the metal-O stretchifig vibration. The band around 3630 cm-1 is interpreted as the O-H stretching vibration arising from water contamination. At higher coverages, a third band emerges (550 cm-1). It is attributed to an optical surface phonon and associated with a preliminary stage of bulk oxide formation.