Experimental and Theoretical Study on Dissociative Photoionization of Cyclopentanone

The dissociative photoionization of cyclopentanone was investigated by means of a reflectron time-of-flight mass spectrometer (RTOF-MS) with tunable vacuum ultraviolet synchrotron radiation in the photon energy range of 9.0-15.5 eV. The photoionization efficiency (PIE) curves for molecular ion and fragment ions were measured. The ionization energy of cyclopentanone was determined to be 9.23 +/- 0.03 eV. Fragment ions from the dissociative photoionization of cyclopentanone were identified as C5H7O+, C4H5O+, C4H8+/C3H4O+, C3H3O+, C4H6+, C2H4O+, C3H6+, C3H5+, C3H4+, C3H3+, C2H5+ and C2H4+. With the aid of the ab initio calculations at the omega B97X-D/6-31+G(d,p) level of theory, the dissociative mechanisms of C5H8O+ are proposed. Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.