Isomeric signatures in the fragmentation of pyridazine and pyrimidine induced by fast ion impact

Abstract

We present fast proton impact induced fragmentations of pyrimidine and pyridazine as an experimental resource to investigate isomeric signatures. Major isomeric imprints are identified for few fragment ions and differences of more than an order of magnitude for the cross sections of fragments of the same mass were measured. The observation of the molecular structure of these isomers gives no apparent indication for the reasons for such substantial differences. It is verified that the simple displacement of the position of one nitrogen atom strongly inhibits or favors the production of some ionic fragment species. The dependency of the fragmentation cross sections on the proton impact energy, investigated by means of time of flight mass spectroscopy and of a model calculation based in first order perturbation theory, allows us to disentangle the complex collision dynamics of the ionic fragments. The proton-induced fragmentation discriminates rather directly the association between a molecular orbital ionization and the fragment-ions creation and abundance, as well as how the redistribution of the energy imparted to the molecules takes place, triggering not only single but also double vacancy and leads to specific fragmentation pathways.

Electron impact ionization and cationic fragmentation of the pyridazine molecules

“…The characteristic feature noticed in the fragmentation of pyridazine parent cation was loss of the N 2 and HCN stable neutral molecules from the molecular ring. The mass spectra of pyridazine have been also explored using fast (keV) proton impact fragmentation [16] and charge exchange with low kinetic energy positive ions [17]. Fragmentation patterns in pyridazine have also been investigated by photoionization mass spectroscopy in the 13.8-23.0 eV photon energy range.…”

Branching ratios for the fragmentation pathways leading to C2H2+in electron–ethylene collisions

“…Moreover, the ethylene parent ion is the simplest π radical system [14], and, therefore, comprehension of its relaxation processes leading to the release of one or more hydrogen atoms from the ethylene cation is important to provide a better picture for both theoretical models describing the fragmentation processes of organic compounds [15,16] and quantitative estimates of subsequent reactions such fragments may further undergo on their respective environments [17,18]. Furthermore, it is known that larger hydrocarbons, from ethane [19] to complex cyclic organic molecules [20][21][22] have a tendency of releasing ethylene-and acetylene-like charged and neutral fragments, C 2 H n , in breakup processes following irradiation.…”