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 $\pm$ 0.03 eV. Fragment ions from the dissociative photoionization of cyclopentanone were identified as C $_5$ H $_7$ O $^+$ , C $_4$ H $_5$ O $^+$ , C $_4$ H $_8^+$ /C $_3$ H $_4$ O $^+$ , C $_3$ H $_3$ O $^+$ , C $_4$ H $_6^+$ , C $_2$ H $_4$ O $^+$ , C $_3$ H $_6^+$ , C $_3$ H $_5^+$ , C $_3$ H $_4^+$ , C $_3$ H $_3^+$ , C $_2$ H $_5^+$ and C $_2$ H $_4^+$ . 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 C $_5$ H $_8$ O $^+$ are proposed. Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.