Surface pump-probe femtosecond-laser mass spectrometry: Time-, mass-, and velocity-resolved detection of surface reaction dynamics

Vaida, Mihai E.; Bernhardt, Thorsten M.

doi:10.1063/1.3488098

Cited by 11 publications

(23 citation statements)

References 61 publications

(53 reference statements)

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“…The CD 3 + transient signal consists of a peak structure with a maximum at 50 fs. The interpretation of this transient is based on earlier experiments with methyl iodide on an insulating magnesia surface and on the power dependences of the pump and the probe laser, which support a single-photon excitation followed by a two-photon ionization [18,38–39]. …”

Section: Resultsmentioning

confidence: 94%

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Femtosecond time-resolved photodissociation dynamics of methyl halide molecules on ultrathin gold films

Vaida¹,

Tchitnga²,

Bernhardt³

2011

Beilstein J. Nanotechnol.

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SummaryThe photodissociation of small organic molecules, namely methyl iodide, methyl bromide, and methyl chloride, adsorbed on a metal surface was investigated in real time by means of femtosecond-laser pump–probe mass spectrometry. A weakly interacting gold surface was employed as substrate because the intact adsorption of the methyl halide molecules was desired prior to photoexcitation. The gold surface was prepared as an ultrathin film on Mo(100). The molecular adsorption behavior was characterized by coverage dependent temperature programmed desorption spectroscopy. Submonolayer preparations were irradiated with UV light of 266 nm wavelength and the subsequently emerging methyl fragments were probed by photoionization and mass spectrometric detection. A strong dependence of the excitation mechanism and the light-induced dynamics on the type of molecule was observed. Possible photoexcitation mechanisms included direct photoexcitation to the dissociative A-band of the methyl halide molecules as well as the attachment of surface-emitted electrons with transient negative ion formation and subsequent molecular fragmentation. Both reaction pathways were energetically possible in the case of methyl iodide, yet, no methyl fragments were observed. As a likely explanation, the rapid quenching of the excited states prior to fragmentation is proposed. This quenching mechanism could be prevented by modification of the gold surface through pre-adsorption of iodine atoms. In contrast, the A-band of methyl bromide was not energetically directly accessible through 266 nm excitation. Nevertheless, the one-photon-induced dissociation was observed in the case of methyl bromide. This was interpreted as being due to a considerable energetic down-shift of the electronic A-band states of methyl bromide by about 1.5 eV through interaction with the gold substrate. Finally, for methyl chloride no photofragmentation could be detected at all.

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Section: Resultsmentioning

confidence: 94%

“…Mass measurements were carried out on a homebuilt time-of-flight mass spectrometer [18,39]. The grounded Au/Mo(100) substrate served as the repeller electrode of a Wiley–McLaren-type acceleration lens arrangement [41].…”

Section: Methodsmentioning

confidence: 99%

Femtosecond time-resolved photodissociation dynamics of methyl halide molecules on ultrathin gold films

Vaida¹,

Tchitnga²,

Bernhardt³

2011

Beilstein J. Nanotechnol.

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“…One year later, the group published a paper again concerning MgO and CH 3 I/CD 3 I system, but with stronger focus on the experimental procedures (Vaida & Bernhardt, ). The surface photoexcitation, the resonant multiphoton ionization detection scheme and the time‐resolved pump‐probe measurements were explained in greater detail, as were the photodissociation dynamics.…”

Section: Photodissociationmentioning

confidence: 99%

Photoionization and photofragmentation in mass spectrometry with visible and UV lasers

Gunzer

Krüger

Grotemeyer

2018

Mass Spectrometry Reviews

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Ever since the introduction of laser technology to the field of mass spectrometry, several disciplines evolved providing solutions to challenging scientific and analytical tasks in research and industry. Among these are techniques involving multiphoton ionization such as Resonance‐Enhanced Multiphoton Ionization (REMPI, R2PI) and Mass‐Analyzed Threshold Ionization (MATI) spectroscopy, a variant of Zero Kinetic Energy (ZEKE) spectroscopy, that possess the ability to selectively ionize certain preselected compounds out of complex mixtures, for example, environmental matrices, with a high level of efficiency. Another key feature of multiphoton ionization techniques is the ability to control the degree of fragmentation, whereas soft ionization is most highly appreciated in most applications. In cases where rich fragmentation patterns are desired for diagnostic purposes, Photodissociation mass spectrometry (PD‐MS) is applied successfully. PD‐MS allows for the cleavage of selected chemical bonds. With the introduction of chromophoric labels in PD‐MS, it became possible to target certain molecules or groups within a molecule. In this review article, an overview of the basic principles and experimental requirements of REMPI and MATI spectroscopy and PD mass spectrometry are given. By means of selected examples, the latest developments and application possibilities in this field over the past decade with special focus on the German research landscape are pointed out. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 38: 202–217, 2019.

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“…Nevertheless, the direct time-and mass-resolved detection of the transition state and the product formation dynamics of a bimolecular surface reaction as proposed by Polanyi and Zewail has been realized only very recently employing the new approach of surface pump-probe femtosecond-laser mass spectrometry. 6,7 This technique relies on the combination of time-of-flight mass spectrometry with non-resonant or resonance enhanced multi-photon ionization (REMPI) detection and fast surface preparation by a pulsed molecular beam. 7 Ultrathin oxide films serve as versatile substrates that interact only weakly with adsorbed molecules.…”

Section: Introductionmentioning

confidence: 99%

Surface-aligned femtochemistry: Photoinduced reaction dynamics of CH3I and CH3Br on MgO(100)

Vaida

Bernhardt

2012

Faraday Discuss.

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Methyl iodide and methyl bromide molecules were adsorbed at submonolayer coverages on an ultrathin MgO(100) film on Mo(100) and photoexcited by 266 nm femtosecond-laser irradiation. The subsequent photodissociation and desorption dynamics were probed by time delayed multi photon ionization mass spectrometric detection of the emerging reaction products. The pronounced difference in the appearance times of the methyl radical fragments from methyl iodide and bromide is discussed on the basis of the different molecular adsorption geometries on magnesia. The surface adsorption structure also defines the alignment of the encounter complex for the observed bimolecular formation of the halogen molecules I2 and Br2 within about 1 and 2 ps, respectively. Finally, photoexcitation of co-adsorption layers of CH3I and CH3Br resulted in a heteronuclear bi-molecular reaction yielding IBr molecules.

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Surface pump-probe femtosecond-laser mass spectrometry: Time-, mass-, and velocity-resolved detection of surface reaction dynamics

Cited by 11 publications

References 61 publications

Femtosecond time-resolved photodissociation dynamics of methyl halide molecules on ultrathin gold films

Femtosecond time-resolved photodissociation dynamics of methyl halide molecules on ultrathin gold films

Photoionization and photofragmentation in mass spectrometry with visible and UV lasers

Surface-aligned femtochemistry: Photoinduced reaction dynamics of CH3I and CH3Br on MgO(100)

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