Comprehensive survey of dissociative photoionization of quinoline by PEPICO experiments

Abstract

Dissociative photoionisation of quinoline induced by VUV radiation is investigated using photoelectron photoion coincidence (PEPICO) spectroscopy. Branching ratios of all the detectable fragment ions are measured as a function of internal energy ranging from 2 to 30 eV. A specific generation hierarchy is observed in the breakdown curves of a set of dissociation channels. Moreover, a careful comparison of the breakdown curves of fragments among the successive generations allowed to establish a decay sequence in the fragmentation of quinoline cation. This enabled us to revisit and refine the understanding of the first generation decay and reassign the origin of few of the higher generation decay products of quinoline cation. With the help of the accompanying computational work (reported concurrently) we have demonstrated the dominance of two different HCN elimination pathways over previously interpreted mechanisms. For the first time a specific pathway for acetylene elimination is identified in quinoline+ and the role of isomerization in both acetylene as well as hydrogen cyanide loss is also clearly demonstrated. The experiment also established that the acetylene elimination exclusively occurs from the non-nitrogen containing ring of quinoline cation. The formation of a few astronomically important species is also discussed.

In search of universalities in the dissociative photoionization of PANHs via isomerizations

“…For instance, it was shown both theoretically and experimentally that naphthalene prefers to isomerize to azulene prior to C 2 H 2 abstraction. 31,32 A similar observation has been reported in the case of quinoline, a nitrogenated analog of naphthalene 19,33 for the cases of HCN and C 2 H 2 abstractions. This was also extended to larger ring structures; 34 for instance, acridine and phenanthridine were shown to preferentially isomerize to common structures before further dissociation.…”

“…[24][25][26] Its detection in the interstellar medium 27 in large quantities prompts the question of their production mechanism given its rapid isomerization to HCN in the presence of solid interfaces (grains, dust). Similarly, other astronomically relevant molecules, such as members of the cyanopolyyne family, have also been detected 19,28 as fragments from the dissociation of PANHs. Hence, a detailed study of the dissociative processing of PANHs and the formed products would provide great insights into their role in chemical evolution in space.…”

“…One of such important fragments is hydrogen cyanide (HCN), known to be one of the dominant neutrals products in the dissociation of many different PANHs. 18,19 Adenine, one of the four nucleobases in DNA, is a pentamer of HCN, and various studies 20,21 have established the importance of HCN in adenine's formation even in environments analogous to extremely cold interstellar clouds. 22 Another interesting example is hydrogen iso-cyanide (HNC), which is also produced as a dominant neutral product 23 in dissociative processes.…”

Fingerprinting fragments of fragile interstellar molecules: dissociation chemistry of pyridine and benzonitrile revealed by infrared spectroscopy and theory

“…A variety of studies has been investigating the fragmentation processes of astronomical relevant molecules in detail ranging from theoretical [29][30][31] to experimental studies using dissociative ionization and infrared spectroscopy [32][33][34][35][36][37] or imaging Photoelectron-Photoion-Coincidence (iPEPICO) spectroscopy [38][39][40] . By using a combination of techniques, some of these studies have provided structural information of the fragment ions.…”

Competition between Loss of H2 versus H+H in the Fragmentation of the Fluorene Cation

“…At higher energies (Figure 5), in the range of up to five absorbed photons, [57] corresponding to about 14 eV of excitation energy, up to 3H loss are experimentally observed. These results invalidate the possibility of no H pairing, since the AE for 3H channels would be 15 eV (Figure 2, top).…”