Cryogenic Messenger-IR Ion Spectroscopy Study of Phenol & Aniline Molecular Ions and of the common Fragment Ion [C5H6]+ formed by EI-MS

Spectroscopic Detection of Cyano-Cyclopentadiene Ions as Dissociation Products upon Ionization of Aniline

“… Experimental mass spectra showing the ionization and fragmentation of aniline in (a) the storage ion source at 40 eV and (b) the direct electron impact source at electron energies of 20 eV 33 (black) and 50 eV (pink). The most important fragmentation channels C 6 H 6 N + ( m / z 92, H loss), C 5 H 6 •+ ( m / z 66, HNC loss), and C 5 H 5 + or C 4 H 3 N •+ ( m / z 65, HNCH or C 2 H 4 loss) are labeled.…”

“…Using cryogenic infrared messenger spectroscopy, the structures of the aniline parent ion ( m / z 93) and the HNC fragment ( m / z 66), formed at an electron energy of 20 eV, have been investigated and structurally assigned to the canonical aniline •+ radical cation and the cyclopentadiene •+ radical cation structure, respectively. 33 The same experimental approach is used here to elucidate the experimental structure of the H-loss product. The spectroscopic measurements were performed with the storage ion source using an electron impact ionization with 15 eV electrons.…”

“…Pathway 3 includes the isomerization and fragmentation to C 5 H 6 •+ upon the loss of HNC, where the product ion has been experimentally observed under similar ionization conditions as in this study and assigned to the cyclopentadiene •+ radical cation ( 8 ). 33 On this isomerization pathway, the H-loss branch has been calculated from the intermediate structure ( 6 ) resulting in ( 10 ). Structure 10 is calculated to be 392 kJ/mol higher with respect to the aniline •+ , thereby higher than azatropylium + but slightly lower than the anilino + ion.…”

“…established that the fragmentation occurred to the cyclopentadiene radical cation with the ejection of neutral hydrogen isocyanide (HNC). Using cryogenic infrared messenger spectroscopy, the structures of the aniline parent ion ( m / z 93) and the HNC fragment ( m / z 66), formed at an electron energy of 20 eV, have been investigated and structurally assigned to the canonical aniline •+ radical cation and the cyclopentadiene •+ radical cation structure, respectively . The same experimental approach is used here to elucidate the experimental structure of the H-loss product.…”

“…Here, we study the dissociative ionization pathways of the nitrogen containing aromatic molecule aniline (aminobenzene), the simplest aromatic amine, upon hydrogen atom (H) loss and provide a spectroscopic identification of the ionic H-loss fragment (C 6 H 6 N + ). We apply sensitive infrared predissociation (IRPD) action spectroscopy in a cryogenic ion trap instrument coupled to the free electron laser for infrared experiments (FELIX) to investigate the mass-selected ionic fragments formed upon dissociative ionization of neutral aniline, a method that we have previously applied to identify the HNC- and CO-loss fragment ion of aniline and phenol, respectively, as well as the H-loss fragment ions of larger aromatic species. , The observed structures provide additional information on the isomerization and fragmentation pathways of aniline compared to previous theoretical and experimental studies. The spectroscopic identification of the different fragmentation pathways of aniline can point toward new astronomically relevant molecules that are likely to exist in both Titan’s atmosphere and cold molecular clouds.…”