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

Abstract

The cationic fragmentation products in the dissociative ionization of pyridine and benzonitrile have been studied by infrared action spectroscopy in a cryogenic ion trap instrument at the Free-Electron Lasers for...

Threshold photoelectron spectroscopy and dissociative photoionization of benzonitrile

“…The isomerization can proceed via a single transition state from phenylacetylene˙ + , and via a second pathway that contains an additional intermediate state. The latter pathway is the lowest in energy and also analogous to the suggested pathway by Rap et al 29 for HCN/HNC loss of benzonitrile˙ + .…”

“…A recent study utilized infrared predissociation (IRPD) spectroscopy to characterize the structures of the ionic fragments formed from electron-induced dissociative ionization of benzonitrile. 29 The dominant HCN/HNC loss, at an electron energy of 15 eV, was found to result in ortho-benzyne + and bicyclic meta-benzyne + (BMB + ) C 6 H 4 + fragment ions. The latter was only found to be a minor contributor to the spectrum.…”

“…Surprisingly, the m / z 50 peak, reported to be a major fragment ion by Molenaar-Langeveld et al , 28 was not observed. 29…”

“…Surprisingly, the m/z 50 peak, reported to be a major fragment ion by Molenaar-Langeveld et al, 28 was not observed. 29 The dissociation mechanisms of species related to benzonitrile have also gained considerable attention. For example, the VUV photodissociation of protonated benzonitrile (C 6 H 5 CNH + ) was measured by Jacovella et al 17 ) by the loss of the hydrogen (iso)cyanide (HCN or HNC) and cyanoacetylene (HC 3 N), respectively.…”

“…, however, shows the BMB + , likely in combination with the meta-benzyne + isomer, to be the main fragment at low internal energies. Since the work of Rap et al29 is performed at 15 eV electron energy, the dominance of the ortho-benzyne + fragment ion, which lies about 0.3 eV above BMB + , is likely due to faster rising rate constants because of the looser transition state(s) along the fragmentation pathway.At 50 eV electron energy, Rap et al29 report an increase in the m/z 77 and 75 signals. These peaks could be assigned to the phenylium + (c-C 6 H 5 + ) and cyanodiacetylene + (HC 5 N + ) cation, formed via the loss of CN and C 2 H 4 , respectively.…”