Detection of Interstellar Acetone toward the Orion-KL Hot Core

We present the first detection of interstellar acetone [(CH 3 ) 2 CO] toward the high-mass star-forming region Orion-KL and the first detection of vibrationally excited (CH 3 ) 2 CO in the interstellar medium (ISM). Using the BIMA array, 28 emission features that can be assigned to 54 acetone transitions were detected. Furthermore, 37 of these transitions have not been previously observed in the ISM. The observations also show that the acetone emission is concentrated toward the hot core region of Orion-KL, contrary to the distribution of other large oxygen-bearing molecules. From our rotational temperature diagram, we find a beam-averaged (CH 3 ) 2 CO column density of [2.0(0.3)-8.0(1.2)] × 10 16 cm -2 and a rotational temperature of 176(48)-194(66) K.