Electron ionization of different large perfluoroethers embedded in ultracold helium droplets: effective freezing of short‐lived decomposition intermediates. (13th December 2012)

• Record Type: Journal Article
• Authors: Bartl, P.; Tanzer, K.; Mitterdorfer, C.; Karolczak, S.; Illenberger, E.; Denifl, S.; Scheier, P.
• Is Part Of: Rapid communications in mass spectrometry. Volume 27:Number 2(2013)
• Page Start: 298
• Page End: 304
• Publication Date: 2012-12-13
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.6459
• Languages: English
• ISSNs: 0951-4198

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="rcm6459-sec-0001" sec-type="section"> <title>RATIONALE</title> <p>Electron ionization of three perfluoroethers (PFEs), C<sub>6</sub>F<sub>14</sub>O<sub>3</sub>, C<sub>8</sub>F<sub>18</sub>O<sub>4</sub>, and C<sub>10</sub>F<sub>20</sub>O<sub>5</sub>, is studied in the gas phase and when the molecules are embedded in ultracold helium (He) droplets. The molecules investigated are model compounds for perfluoropolyethers used as lubricants in technical applications. The present study gives insight into possible radiolysis pathways upon radiation exposure.</p> </sec> <sec id="rcm6459-sec-0002" sec-type="section"> <title>METHODS</title> <p>The experiments utilized a crossed electron/droplet beam apparatus consisting of a He droplet source and pick‐up chamber combined with a commercial time‐of‐flight mass spectrometer. The doped droplets were ionized by electron ionization at 70 eV.</p> </sec> <sec id="rcm6459-sec-0003" sec-type="section"> <title>RESULTS</title> <p>The He environment strongly affects the ionization patterns in the way that both the molecular ion M<sup>+</sup> and high‐mass fragment ions formed by the loss of light neutral species such as F ([M–F]<sup>+</sup>), or CF<sub>3</sub>OCF<sub>2</sub> ([M–CF<sub>3</sub>OCF<sub>2</sub>]<sup>+</sup>), etc., became strong signals in the mass spectrum. These signals were not or only barely visible in the gas‐phase experiment and were identified as short lived (< µs) dissociation intermediates which in the gas phase immediately decomposed into lower‐mass fragment ions.</p> </sec> <sec id="rcm6459-sec-0004" sec-type="section"> <title>CONCLUSIONS</title> <p>Ionic fragmentation intermediates are frozen and subsequently stabilized in the He environment. Helium droplets can hence be viewed as a cryogenic laboratory transforming short‐lived decomposition intermediates into stable fragment ions appearing as strong signals in the mass spectrum. Copyright © 2012 John Wiley & Sons, Ltd.</p> </sec> </abstract>