Postionization of molecules desorbed from surfaces by keV ion bombardment with femtosecond laser pulses

Willey, K. F.; Vorsa, Vasil; Braun, Robert M.; Winograd, Nicholas

doi:10.1002/(sici)1097-0231(19980930)12:18<1253::aid-rcm317>3.0.co;2-h

Cited by 33 publications

(49 citation statements)

References 29 publications

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“…36,37 The discovery of ion/ surface reactions that are sensitive to closely related chemical species should make it possible to extend the scope of this methodology for adsorbate characterization. The fact that ion/ surface inelastic processes can provide data even for fractional monolayer coverages should increase the potential value of this approach.…”

Section: Discussionmentioning

confidence: 99%

Adsorbate Geometry Distinction in Arenethiols by Ion/Surface Reactive Collisions

et al. 1999

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Reactive scattering of low-energy ions from surfaces gives scattered product ions in which new bonds are formed with the adsorbate with a sensitivity to adsorbate geometry. Reactions of Cr •+ and C 5 H 5 N •+ , as well as chemical sputtering induced by Xe •+ , are used to distinguished two well-characterized monolayer systems, namely 1,4-benzenedimethanethiol (BDMT) adsorbed on Au(111) and Ag(111) thin films. While the reaction of Cr •+ with the Au monolayer produces an ion assigned as CrC 7 H 5 S + , this product is completely absent upon reaction with the Ag monolayer. Pyridine (C 5 H 5 N •+ ) projectiles abstract C 1 -C 8 hydrocarbon groups in 50 eV collisions with the Au monolayer, while the Ag monolayer shows only C 1 -C 4 abstraction with a significantly different intensity pattern. Chemical sputtering (Xe •+ ) mass spectra of the two surfaces are substantially different; complete fragmentation of the Ag adsorbate occurs, leading to C 2 -C 4 ion ejection, while more of the molecular features are preserved in the spectrum recorded for the Au monolayer. The experimental facts are interpreted in terms of the geometry of the BDMT molecule that is monocoordinated on Au and dicoordinated on Ag. The experiments are extended to the 1,2-and 1,3-ring isomers of 1,4-BDMT, which have not been characterized by other forms of surface spectroscopy. Ion/surface reactive collisions are useful for characterizing chemisorbates, including their geometrical orientation.

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Section: Discussionmentioning

confidence: 99%

Adsorbate Geometry Distinction in Arenethiols by Ion/Surface Reactive Collisions

et al. 1999

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“…Alkali element contamination has been reported in similar spectra of aromatic amino acids (Karas et al 1985;Willey et al 1998;Plekan et al 2008). Furthermore, systematic analysis of their isotopic distribution supports the presence of alkali elements and their subsequent interaction with the phenylalanine and thenardite moieties.…”

Section: Resultsmentioning

confidence: 61%

“…The additional loss of the O from the C 7 H 7 O + ion leads to the C 7 H 7 + fragment ion (m/z 91). (Willey et al 1998;Plekan et al 2008). 4(c)) is observed by successive cleaving of the amine group ([M-NH 2 ]) and the carboxyl group ([M-COOH]) at m/z 165 and 136, respectively.…”

Section: Resultsmentioning

confidence: 99%

Effect of thenardite on the direct detection of aromatic amino acids: implications for the search for life in the solar system

Richardson

Hinman

Scott

2009

International Journal of Astrobiology

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With the discovery of Na-sulphate minerals on Mars and Europa, recent studies using these minerals have focused on their ability to assist in the detection of bio/organic signatures. This study further investigates the ability of thenardite (Na 2 SO 4 ) to effectively facilitate the ionization and identification of aromatic amino acids (phenylalanine, tyrosine and tryptophan) using a technique called geomatrix-assisted laser desorption/ionization in conjunction with a Fourier transform ion cyclotron resonance mass spectrometry. This technique is based on the ability of a mineral host to facilitate desorption and ionization of bio/organic molecules for detection. Spectra obtained from each aromatic amino acid alone and in combination with thenardite show differences in ionization mechanism and fragmentation patterns. These differences are due to chemical and structural differences between the aromatic side chains of their respective amino acid. Tyrosine and tryptophan when combined with thenardite were observed to undergo cation-attachment ([M+Na] + ), due to the high alkali ion affinity of their aromatic side chains. In addition, substitution of the carboxyl group hydrogen by sodium led to formation of [M-H+Na]Na + peaks. In contrast, phenylalanine mixed with thenardite showed no evidence of Na + attachment. Understanding how co-deposition of amino acids with thenardite can affect the observed mass spectra is important for future exploration missions that are likely to use laser desorption mass spectrometry to search for bio/organic compounds in extraterrestrial environments.

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“…Experiments were performed using a TOF-MS instrument which has been described in detail, previously [15]. Molecules were desorbed using a pulsed 40 keV C 60 ion source (Ionoptika, Ltd.) by focusing a 50 pA beam, measured in direct current mode, to a 5 µm diameter spot on the sample.…”

Section: Methodsmentioning

confidence: 99%

Strong-field ionization of sputtered molecules for biomolecular imaging

Willingham

Kucher

Winograd

2009

Chemical Physics Letters

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Photoionization of molecules sputtered from molecular thin films has been achieved using high field 125 fs pulses in the mid-IR spectral range. Using several model systems, we show that it is possible to significantly reduce molecular fragmentation induced by the laser field by increasing the photoionization wavelength. By examining the photoionization spectra as a function of wavelength, it is apparent that the photoionization mechanism is changing from a non-adiabatic multi-electron excitation process to a process that involves tunnel ionization. The results of these observations are discussed in terms of their significance for bioimaging with focused ion beams and massspectrometry.

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Postionization of molecules desorbed from surfaces by keV ion bombardment with femtosecond laser pulses

Cited by 33 publications

References 29 publications

Adsorbate Geometry Distinction in Arenethiols by Ion/Surface Reactive Collisions

Adsorbate Geometry Distinction in Arenethiols by Ion/Surface Reactive Collisions

Effect of thenardite on the direct detection of aromatic amino acids: implications for the search for life in the solar system

Strong-field ionization of sputtered molecules for biomolecular imaging

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