Uni- and bi-molecular reactions involving Criegee intermediates (CIs), characteristic to alkene-ozone reactions, play an important role in synthetic organic, atmospheric, and combustion chemistry. However, difficulty in detecting key intermediates has prevented a thorough understanding of the details of the ozonolysis mechanism. To gain new insights into how alkene structure affects the CI network, the ozone assisted oxidation reactions of trans-2-pentene and cyclopentene are investigated between 320 K and 760 K in an atmospheric pressure jet stirred reactor (JSR). Molecular-beam mass spectrometry in conjunction with single photon tunable synchrotron VUV radiation is used to identify elusive intermediates by means of experimental photoionization energy scans and ab initio threshold energy calculation for isomer identification. To determine the locally adiabatic ionization energy of structures of interest, density functional theory calculations of the ground state energy of the cation and neutral species are carried out at the M06-2X/AUG-cc-PVTZ level of theory. The CIs formed in the ozonolysis of trans-2-pentene are observed to react bimolecularly with aldehydes to form high molecular weight products. No products corresponding to CI bimolecular reaction are observed in the ozone assisted oxidation reaction of cyclopentene, suggesting decomposition as the primary fate of the long-chain CI. Threshold ionization energy calculations suggest detection of the ketohydroperoxide intermediates, 2-hydroperoxypentan-3-one and 2-hydroperoxycyclopentanone in the ozone assisted oxidation of trans-2-pentene and cyclopentene, respectively. The results of these studies provide new mechanistic insights into ozone assisted oxidation reactions of two alkenes with the same carbon number, but different structure, which is critical for the development of improved kinetics models.