| 1. |
- Ganguly, Smita, et al.
(author)
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The origin of enhanced O2+ production from photoionized CO2 clusters
- 2022
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In: Communications Chemistry. - 2399-3669.
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Journal article (peer-reviewed)abstract
- CO2-rich planetary atmospheres are continuously exposed to ionising radiation driving major photochemical processes. In the Martian atmosphere, CO2 clusters are predicted to exist at high altitudes motivating a deeper understanding of their photochemistry. In this joint experimental-theoretical study, we investigate the photoreactions of CO2 clusters (≤2 nm) induced by soft X-ray ionisation. We observe dramatically enhanced production of O2- from photoionized CO2 clusters compared to the case of the isolated molecule and identify two relevant reactions. Using quantum chemistry calculations and multi-coincidence mass spectrometry, we pinpoint the origin of this enhancement: A size-dependent structural transition of the clusters from a covalently bonded arrangement to a weakly bonded polyhedral geometry that activates an exothermic reaction producing O+2. Our results unambiguously demonstrate that the photochemistry of small clusters/particles will likely have a strong influence on the ion balance in atmospheres.
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| 2. |
- Kyrö, Riikka, et al.
(author)
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Student-oriented, supervisor-led, or externally-driven : balancing the supervision a modern doctorate
- 2019
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In: ; , s. 8-9
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Conference paper (peer-reviewed)abstract
- Doctoral education in the technical fields has several distinct features, such as, the research is often projectbased, interdisciplinary, dependent on external funding, and affiliated with an industry. In other words, the epitome of a “modern doctorate” (Fillery-Travis, 2017; Lee, 2018). While literature on doctoral supervision in general is abundant (see e.g. Gatfield, 2005; Gurr, 2001; Ives & Rowley, 2005; Kobayashi, Grout, & Rump, 2015; Lee, 2008, 2012; Lindén, 2005; Lindén, Ohlin, & Brodin, 2013), supervision specifically in the technical fields has received less discussion. Haksever & Manisali (2002) study discrepancies between the expected and received supervision in an engineering field in the UK, and conclude that effective communication is critical. Grevholm, Persson, & Wall (2005) present a supervision model developed andused in Luleå University of Technology. Smit (2010) discusses the access to research community in engineering sciences, and sees it affected by the requirement of independence and power relations. Finally, two Danish studies focus on supervision practices in the context of international PhD students in engineering (Bøgelund & Graaff, 2015; Kolmos, Kofoed, & Du, 2008). This study attempts to fill the research gap with empirical evidence, focusing on factors influencing supervision style specifically in the technical fields. The study employs a qualitative research approach, and utilizes semi-structured interviews. Altogether 24 interviews were conducted during spring 2019 at institutions linked to Lund University. As the ambition was to capture the perspectives of both supervisors and students, the informants comprised 13 supervisors and 11 doctoral candidates. Interviews focused on communication practices, and the supervisory relationship. The interview protocol was followed loosely to allow important issues to emerge from an open discussion. The study identifies several influencing factors, that may be roughly divided into three categories. Factors identified in the Student category comprise the personal characteristics and maturity of the doctoral student. Similarly, factors in the Supervisor category include the personality and professional experience of the supervisor, but also the dynamics between main and co-supervisor(s). Interestingly, communicationpractices, which may be either very formal (scheduled meetings with minutes) or informal (ad-hoc discussions) do not necessarily reflect the relationship of the student and supervisor. Rather, the practices are often affected by External factors, such as institutional or departmental policies (statutory planning meetings, open door policy), or the project-based nature of the research work (project timeline). Based on the findings, this study presents three doctoral supervision approaches, the student oriented, the supervisor-led, and the externally-driven. Most interviewed supervisors maintain that their supervision is always adapted to the individual student, emphasizing the student-centered approach. However, the supervisors’ own preferences regarding e.g. communication practices play a significant role. Moreover,external issues, such as top-down policies, limit the possibilities of adaptation. In conclusion, doctoral supervision is most often a mix of the different approaches. The results of this study allow supervisors to reflect on their own supervision style, presenting a selection of potential approaches to supervision. The three approaches and their underlying factors may be particularly useful for researchers at the beginning of their supervising careers, or to be used as examples in higher pedagogy training.
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| 3. |
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| 4. |
- Oghbaiee, Shabnam, et al.
(author)
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Site-dependent nuclear dynamics in core-excited butadiene
- 2022
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In: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 24:47, s. 28825-28830
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Journal article (peer-reviewed)abstract
- Symmetry breaking and competition between electronic decay and nuclear dynamics are major factors determining whether the memory of the initial core-hole localisation in a molecule is retained long enough to affect fragmentation. We investigate the fate of core holes localised at different sites in the free 1,3 trans butadiene molecule by using synchrotron radiation to selectively excite core electrons from different C 1s sites to π* orbitals. Fragmentation involving bonds localised at the site of the core hole provides clear evidence for preferential bond breaking for a core hole located at the terminal carbon site, while the signature of localisation is weak for a vacancy on the central carbon site. The origin of this difference is attributed to out-of-plane vibrations, and statistical evaporation of protons for vacancies located at the central carbon sites.
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| 5. |
- Oostenrijk, Bart, et al.
(author)
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Fission of charged nano-hydrated ammonia clusters - microscopic insights into the nucleation processes
- 2019
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 21:46, s. 25749-25762
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Journal article (peer-reviewed)abstract
- While largely studied on the macroscopic scale, the dynamics leading to nucleation and fission processes in atmospheric aerosols are still poorly understood at the molecular level. Here, we present a joint experimental-theoretical study of a model system consisting of hydrogen-bonded ammonia and water molecules. Experimentally, the clusters were produced via adiabatic co-expansion. Double ionization ionic products were prepared using synchrotron radiation and analyzed with coincidence mass- and 3D momentum spectroscopy. Calculations were carried out using ab initio molecular dynamics to understand the fragmentation within the first similar to 500 fs. Further exploration of the potential energy surfaces was performed at a DFT level of theory to gain information on the energetics of the processes. Water was identified as an efficient nano-droplet stabilizer, and is found to have a significant effect even at low water content. On the molecular level, the stabilizing role of water can be related to an increase in the dissociation energy between ammonia molecules and the water enriched environment at the cluster surface. Furthermore, our results support the role of ammonium as a charge carrier in the solution, preferentially bound to surrounding ammonia molecules, which can influence the atmospheric nucleation process.
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| 6. |
- Oostenrijk, Bart, et al.
(author)
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The role of charge and proton transfer in fragmentation of hydrogen-bonded nanosystems : The breakup of ammonia clusters upon single photon multi-ionization
- 2018
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:2, s. 932-940
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Journal article (peer-reviewed)abstract
- The charge and proton dynamics in hydrogen-bonded networks are investigated using ammonia as a model system. The fragmentation dynamics of medium-sized clusters (1-2 nm) upon single photon multi-ionization is studied, by analyzing the momenta of small ionic fragments. The observed fragmentation pattern of the doubly- and triply-charged clusters reveals a spatial anisotropy of emission between fragments (back-to-back). Protonated fragments exhibit a distinct kinematic correlation, indicating a delay between ionization and fragmentation (fission). The different kinematics observed for channels containing protonated and unprotonated species provides possible insights into the prime mechanisms of charge and proton transfer, as well as proton hopping, in such a nanoscale system.
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| 7. |
- Preobrajenski, Alexei, et al.
(author)
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FlexPES : a versatile soft X-ray beamline at MAX IV Laboratory
- 2023
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In: Journal of Synchrotron Radiation. - 0909-0495. ; 30, s. 831-840
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Journal article (peer-reviewed)abstract
- FlexPES is a soft X-ray beamline on the 1.5 GeV storage ring at MAX IV Laboratory, Sweden, providing horizontally polarized radiation in the 40-1500 eV photon energy range and specializing in high-resolution photoelectron spectroscopy, fast X-ray absorption spectroscopy and electron-ion/ion-ion coincidence techniques. The beamline is split into two branches currently serving three endstations, with a possibility of adding a fourth station at a free port. The refocusing optics provides two focal points on each branch, and enables either focused or defocused beam on the sample. The endstation EA01 at branch A (Surface and Materials Science) is dedicated to surface- and materials-science experiments on solid samples at ultra-high vacuum. It is well suited not only to all flavours of photoelectron spectroscopy but also to fast (down to sub-minute) high-resolution X-ray absorption measurements with various detectors. Branch B (Low-Density Matter Science) has the possibility to study gas-phase/liquid samples at elevated pressures. The first endstation of this branch, EB01, is a mobile setup for various ion-ion and electron-ion coincidence techniques. It houses a versatile reaction microscope, which can be used for experiments during single-bunch or multi-bunch delivery. The second endstation, EB02, is based on a rotatable chamber with an electron spectrometer for photoelectron spectroscopy studies on primarily volatile targets, and a number of peripheral setups for sample delivery, such as molecular/cluster beams, metal/semiconductor nanoparticle beams and liquid jets. This station can also be used for non-UHV photoemission studies on solid samples. In this paper, the optical layout and the present performance of the beamline and all its endstations are reported.
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| 8. |
- Walsh, Noelle, et al.
(author)
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Molecular dynamics of NH3 induced by core-electron excitation
- 2015
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 17:29, s. 18944-18952
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Journal article (peer-reviewed)abstract
- Nuclear motion in the N1s(-1)4a(1)(1) core-excited state of ammonia is investigated by studying the angular anisotropy of fragments produced in the decay of the highly excited molecule and compared with predictions from ab initio calculations. Two different fragmentation channels (H+/NH2+ and H+/NH+/H) reveal complex nuclear dynamics as the excitation photon energy is tuned through the 4a(1) resonance. The well-defined angular anisotropy of the fragments produced in the dissociation of the molecular dication species suggests a very rapid nuclear motion and the time scale of the nuclear dynamics is limited to the low fs timescale.
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