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We experimentally probed the low-energy electron-induced dissociation of acetonitrile and acetonitrile- d 3 and performed density functional theory calculations to support the experimental results. The previous studies on electron attachment to acetonitrile presented a number of contradictory findings, which we aimed to resolve in the present study. We observed the formation of H - , CH 2 - , CH 3 - , CN - , CCN - , CHCN - and CH 2 CN - anions and the corresponding deuterated fragments for acetonitrile- d 3 by dissociative electron attachment, and measured ion yields curves of each fragment. We saw no evidence for associative electron attachment to form the parent ion in these measurements. We also have measured the kinetic energy and angular distribution of selected fragments using a velocity map imaging (VMI) spectrometer. [ABSTRACT FROM AUTHOR]

We present an experimental study on the stability of cluster cations formed by the assembly of tryptophan or serine moelcules inside charged helium droplets and subsequent droplet evaporation. The stability is probed via collision induced dissociation and mass spectrometry. We focus on the neutral loss of 18 Da that was previously proposed to result in the formation of an amide bond in amino acid clusters. We show that the cluster cations formed by the neutral loss of 18 Da from protonated parent cluster ion precursors are softly, presumably van der Waals, bound similar to the parent and protonated parent cluster cations. Cluster cations formed after neutral loss of 18 Da from the parent cluster cations are strongly bound, indicating the formation of new covalent bonds. Even though we observe a signal at m/z corresponding to dipeptide cations, their collision induced dissociation fragmentation does not allow unambiguous identification of their structure, particularly the amide bond. Our study at cryogenic conditions of He droplets demonstrates that peptide formation by the cluster ion polymerization is not a barrierless process and the formation of amide bonds may depend on activation methods and available catalysts. [ABSTRACT FROM AUTHOR]

While matter is irradiated with highly-energetic particles, it may become chemically modified. Thereby, the reactions of free low-energy electrons (LEEs) formed as secondary particles play an important role. It is unknown to what degree and by which mechanism LEEs contribute to the action of electron-affinic radiosensitisers applied in radiotherapy of hypoxic tumours. Here we show that LEEs effectively cause the reduction of the radiosensitiser nimorazole via associative electron attachment with the cross-section exceeding most of known molecules. This supports the hypothesis that nimorazole is selectively cytotoxic to tumour cells due to reduction of the molecule as prerequisite for accumulation in the cell. In contrast, dissociative electron attachment, commonly believed to be the source of chemical activity of LEEs, represents only a minor reaction channel which is further suppressed upon hydration. Our results show that LEEs may strongly contribute to the radiosensitising effect of nimorazole via associative electron attachment. Radiosensitisers are believed to interfere with cancer cells by dissociating upon interaction with electrons. Here the authors observe instead that the dominant path for nitroimidazolic radiosensitisers involves formation of a non-dissociated radical anion, prerequisite for their accumulation in tumour cells. [ABSTRACT FROM AUTHOR]

Abstract: We present a combined experimental and theoretical study of the interaction of electrons with Bis(pentamethylcyclopentadienyl)titanium(IV) dichloride (Cp2*TiCl2) and difluoride (Cp2*TiF2). We report the experimental measurements of partial cross sections for the dissociative electron attachment (DEA) and the electron ionization (EI) mass spectra of isolated molecules. Estimates of the absolute cross sections are done on the basis of cross-calibration in the case of DEA and on the basis of binary-encounter-Bethe calculation in the case of EI. EI of both molecules is similar, concerning cross section amplitude and fragmentation pattern. DEA is different: DEA to Cp2*TiF2 primarily results in the formation of stable parent anion, while DEA to Cp2*TiCl2 results in the strong fragmentation, primarily into Cl− anion. Possible use of the molecules as the model species for studies of DEA efficiency in postirradiation chemistry is discussed. Graphical abstract: [ABSTRACT FROM AUTHOR]