We present the first detection of complex aldehydes and isomers in threetypical molecular clouds located within 200pc of the center of our Galaxy. We find very large abundances of these complex organic molecules (COMs) inthe central molecular zone (CMZ), which we attribute to the ejection of COMsfrom grain mantles by shocks. The relative abundances of the different COMswith respect to that of CH3OH are strikingly similar for the three sources,located in very different environments in the CMZ. The similar relativeabundances point toward a unique grain mantle composition in the CMZ. Studyingthe Galactic center clouds and objects in the Galactic disk having largeabundances of COMs, we find that more saturated molecules are more abundantthan the non-saturated ones. We also find differences between the relativeabundance between COMs in the CMZ and the Galactic disk, suggesting differentchemical histories of the grain mantles between the two regions in the Galaxyfor the complex aldehydes. Different possibilities for the grain chemistry onthe icy mantles in the GC clouds are briefly discussed. Cosmic rays can play animportant role in the grain chemistry. With these new detections, the molecularclouds in the Galactic center appear to be one of the best laboratories forstudying the formation of COMs in the Galaxy.
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