Novel experimental setup for time-of-flight mass spectrometry ion detection in collisions of anionic species with neutral gas-phase molecular targets.

J C Oller,P. Limão-Vieira,L. Ellis-Gibbings,F. Ferreira da Silva,G. García

doi:10.1140/epjti/s40485-015-0023-9

Abstract

We report a novel experimental setup for studying collision induced products resulting from the interaction of anionic beams with a neutral gas-phase molecular target. The precursor projectile was admitted into vacuum through a commercial pulsed valve, with the anionic beam produced in a hollow cathode discharge-induced plasma, and guided to the interaction region by a set of deflecting plates where it was made to interact with the target beam. Depending on the collision energy regime, negative and positive species can be formed in the collision region and ions were time-of-flight (TOF) mass-analysed. Here, we present data on O2 precursor projectile, where we show clear evidence of O– and O2– formation from the hollow cathode source as well as preliminary results on the interaction of these anions with nitromethane, CH3NO2. The negative ions formed in such collisions were analysed using time-of-flight mass spectrometry. The five most dominant product anions were assigned to H–, O–, NO–, CNO– and CH3NO2–.

Highlights

The study of radiation interactions with key biological constituents at the molecular level, has shown an increasing interest in the last few years, in particular after the pioneering studies of Sanche and co-workers on the resonant formation of DNA strand breaks by low-energy electrons [1, 2]
The electron capture mechanism, electron transfer from the projectile to the molecule, results in a transient negative ion (TNI) formation, which can decay via electron auto-detachment or fragmentation of the precursor anion
We report a novel experimental setup for studying collision induced products resulting from the interaction of anionic beams with a neutral gas-phase molecular target

Summary

Introduction

The study of radiation interactions with key biological constituents at the molecular level, has shown an increasing interest in the last few years, in particular after the pioneering studies of Sanche and co-workers on the resonant formation of DNA strand breaks by low-energy electrons [1, 2]. New radiotherapy techniques based on ion beam irradiation and using nanoparticles as radiosensitizers, concentrate the energy deposition around reduced volumes where, abundant secondary species, e.g. electrons and radicals, are generated. Many elementary collisional processes are not due to direct electron impact but rather depend upon electron transfer, either from neutral [5] or even anionic species [6] These conditions motivated the present work in which a novel experimental system has been developed to study the interaction of negative radical species with biological relevant molecular targets.

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Results and discussion

Conclusions