The composition of secondary organic aerosol (SOA) from the gas phase ozonolysis of 2006 methylenecyclohexane was analyzed in a series of indoor aerosol chamber experiments. Capillary electrophoresis-electrospray ionization-ion trap mass spectrometry (CE/ESI-ITMS) was used for qualitative and quantitative analysis of SOA constituents. A number of dicarboxylic acids in the range Of C-5-C-6, such as adipic acid and glutaric acid, were found as major components of the organic products. Besides these smaller compounds, the formation of higher-molecular-weight compounds were observed under both neutral and acidic conditions. MS/MS experiments were carried out in order to obtain information on the monomer units and the structure of the dimers. MS2 experiments of the two most prominent dimers with a mass-to-charge ratio (m/z) of 257 and m/z 273 yielded common fragments of m/z 83, 129 or 145. Based on the fragmentation patterns, these dimers are tentatively identified as carboxylate ester acids containing a unit of adipic acid in the structure. The dimer with m/z 257 was nearly 60% of the total detected compounds for both the neutral and acidic seed particle experiments.