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\pm0.03 eV. Fragment ions from the dissociative photoionization of cyclopentanone were identified as C_5H_7O^+, C_4H_5O^+, C_4H_8^+/C_3H_4O^+, C_3H_3O^+, C_4H_6^+, C_2H_4O^+, C_3H_6^+, C_3H_5^+, C_3H_4^+, C_3H_3^+, C_2H_5^+ and C_2H_4^+. With the aid of the ab initio calculations at the \omegaB97X-D/6-31+G(d, p) level of theory, the dissociative mechanisms of C_5H_8O^+ are proposed. Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.