The ultraviolet absorption spectrum of acetone vapor has been photographed. The well‐known absorption region in the neighborhood of 3000A, common to all ketones, is found to have on its long wave end a series of discrete absorption bands. The wave‐lengths of many of these bands have been measured and a vibrational analysis is given. A second absorption region beginning about 1960A and extending toward shorter wave‐lengths is found to consist of several groups of bands, the bands within each group being separated by relatively small frequency differences. The analysis of this band system may be accomplished by assuming several energy levels close together in the upper state together with four fundamental frequencies in the upper state and two in the lower. Evidence for further absorption regions extending to below 1200A has been found and the approximate positions of these regions are given. These bands evidently belong to different electron transitions from the others.
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