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1. Electron-impact ionization and ionic fragmentation of O ₂ from threshold to 120 eV energy range

   https://doi.org/10.1142/S0217979221501046  

   Lomsadze, R. A. ; Gochitashvili, M. R. ; Kezerashvili, R. Ya. ; Schulz, M. ( March 2021 , International Journal of Modern Physics B)

   We study the electron-impact induced ionization of O 2 from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows varying and tuning the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results ofmore »cross-sections for inelastic processes and determining mechanisms for the formation of O[Formula: see text] ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.« less
2. New Ionization Processes for Ionizing Nonvolatile Compounds in Mass Spectrometry: The Road of Discovery to Current State-of-the-Art

   https://doi.org/10.1021/jasms.0c00312  

   Trimpin, Sarah ; Moreno-Pedraza, Abigail ; Yenchick, Frank S. ; Hoang, Khoa ; Pophristic, Milan ; Karki, Santosh ; Marshall, Darrell D. ; Lee, Chuping ; Lu, I-Chung ; El-Baba, Tarick J. ; et al ( January 2020 , Journal of the American Society for Mass Spectrometry)

   This Perspective covers discovery and mechanistic aspects as well as initial applications of novel ioni-zation processes for use in mass spectrometry that guided us in a series of subsequent discoveries, in-strument developments, and commercialization. With all likelihood, vacuum matrix-assisted ionization on an intermediate pressure matrix-assisted laser desorption/ionization source without the use of a laser, high voltages, or any other added energy was the defining turning point from which key developments grew that were at the time unimaginable, and continue to surprise us in its simplistic preeminence, and is therefore a special focus here. We, and others, have demonstrated exceptional analyticalmore »utility with-out a complete understanding of the underlying mechanism. Our current research is focused on how best to understand, improve, and use these novel ionization processes through dedicated platform and source developments which convert volatile and nonvolatile compounds from solid or liquid matrices into gas-phase ions for analysis by mass spectrometry using e.g., mass-selected fragmentation and ion mobility spectrometry to provide reproducible, accurate, and sometimes improved mass and drift time resolution. The combination of research and discoveries demonstrated multiple advantages of the new ionization processes and established the basis of the successes that lead to the Biemann Medal and this Perspective. How the new ionization processes relate to traditional ionization is also presented, as well as how these technologies can be utilized in tandem through instrument modification and implementa-tion to increase coverage of complex materials through complementary strengths.« less
3. Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime

   https://doi.org/10.1038/s41467-021-26193-z  

   Lee, J. W. ; Tikhonov, D. S. ; Chopra, P. ; Maclot, S. ; Steber, A. L. ; Gruet, S. ; Allum, F. ; Boll, R. ; Cheng, X. ; Düsterer, S. ; et al ( December 2021 , Nature Communications)

   Abstract Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10–100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times formore »the electronically excited PAH * , PAH +* and PAH 2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH 2+ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.« less
4. Resolving Isomers of Star-Branched Poly(Ethylene Glycols) by IMS-MS Using Multiply Charged Ions

   https://doi.org/10.1021/jasms.0c00045  

   Austin, Calvin A. ; Inutan, Ellen D. ; Bohrer, Brian C. ; Li, Jing ; Fischer, Joshua L. ; Wijerathne, Kanchana ; Foley, Casey D. ; Lietz, Christopher B. ; Woodall, Daniel W. ; Imperial, Lorelie F. ; et al ( January 2020 , Journal of the American Society for Mass Spectrometry)

   Ion mobility spectrometry (IMS) mass spectrometry (MS) centers on the ability to separate gaseous structures by size, charge, shape, and followed by mass-to-charge (m/z). For oligomeric structures, improved separation is hypothesized to be related to the ability to extend structures through repulsive forces between cations electrostatically bonded to the oligomers. Here we show the ability to separate differently branched multiply charged ions of star-branched poly(ethylene glycol) oligomers (up to 2000 Da) regardless of whether formed by electrospray ionization (ESI) charged solution droplets or from charged solid particles produced directly from a surface by matrix-assisted ionization. Detailed structural characterization of isomersmore »of the star-branched compositions was first established using a home-built high-resolution ESI IMS-MS instrument. The doubly charged ions have well-resolved drift times, achieving separation of isomers and also allowing differentiation of star-branched versus linear oligomers. An IMS-MS “snapshot” approach allows visualization of architectural dispersity and (im)purity of samples in a straightforward manner. Analyses capabilities are shown for different cations and ionization methods using commercially available traveling wave IMS-MS instruments. Analyses directly from surfaces using the new ionization processes are, because of the multiply charging, not only associated with the benefits of improved gas-phase separations, relative to that of ions produced by matrix-assisted laser desorption/ionization, but also provide the potential for spatially resolved measurements relative to ESI and other ionization methods.« less
5. Controlling H3+ Formation From Ethane Using Shaped Ultrafast Laser Pulses

   https://doi.org/10.3389/fphy.2021.691727  

   Townsend, Tiana ; Schwartz, Charles J. ; Jochim, Bethany ; P., Kanaka Raju ; Severt, T. ; Iwamoto, Naoki ; Napierala, J. L. ; Feizollah, Peyman ; Tegegn, S. N. ; Solomon, A. ; et al ( June 2021 , Frontiers in Physics)

   An adaptive learning algorithm coupled with 3D momentum-based feedback is used to identify intense laser pulse shapes that control H 3 + formation from ethane. Specifically, we controlled the ratio of D 2 H + to D 3 + produced from the D 3 C-CH 3 isotopologue of ethane, which selects between trihydrogen cations formed from atoms on one or both sides of ethane. We are able to modify the D 2 H + : D 3 + ratio by a factor of up to three. In addition, two-dimensional scans of linear chirp and third-order dispersion are conducted for amore »few fourth-order dispersion values while the D 2 H + and D 3 + production rates are monitored. The optimized pulse is observed to influence the yield, kinetic energy release, and angular distribution of the D 2 H + ions while the D 3 + ion dynamics remain relatively stable. We subsequently conducted COLTRIMS experiments on C 2 D 6 to complement the velocity map imaging data obtained during the control experiments and measured the branching ratio of two-body double ionization. Two-body D 3 + + C 2 D 3 + is the dominant final channel containing D 3 + ions, although the three-body D + D 3 + + C 2 D 2 + final state is also observed.« less