Pure rotational transitions of the simplest Criegee intermediate, CH2OO, were observed for several excited vibrational levels by Fourier-transform microwave spectroscopy combined with a double-resonance technique, and precise rotational constants of vibrationally excited CH2OO were determined. Comparing the experimentally determined vibration-rotation constants with those derived from a high-level ab initio potential energy surface, vibrational assignments were made for the observed levels. The observed intensities of the 1(01)-O-00 rotational lines suggested that the COO bending mode is significantly excited. (C) 2014 Elsevier B.V. All rights reserved.