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- Boguslavskiy, Andrey E., et al.
(författare)
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The Multielectron Ionization Dynamics Underlying Attosecond Strong-Field Spectroscopies
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 335:6074, s. 1336-1340
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Tidskriftsartikel (refereegranskat)abstract
- Subcycle strong-field ionization (SFI) underlies many emerging spectroscopic probes of atomic or molecular attosecond electronic dynamics. Extending methods such as attosecond high harmonic generation spectroscopy to complex polyatomic molecules requires an understanding of multielectronic excitations, already hinted at by theoretical modeling of experiments on atoms, diatomics, and triatomics. Here, we present a direct method which, independent of theory, experimentally probes the participation of multiple electronic continua in the SFI dynamics of polyatomic molecules. We use saturated (n-butane) and unsaturated (1,3-butadiene) linear hydrocarbons to show how subcycle SFI of polyatomics can be directly resolved into its distinct electronic-continuum channels by above-threshold ionization photoelectron spectroscopy. Our approach makes use of photoelectron-photofragment coincidences, suiting broad classes of polyatomic molecules.
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| 4. |
- Gador, Niklas
(författare)
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Curve-crossing quantum wavepacket dynamics - Experiment and theory
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I present experimental and theoretical workon quantum wavepacket dynamics in potential curve-crossings,using gas-phase Rb2 as working media. Particularly, we havefocused on curve-crossing cases with intermediate strengthcoupling, which leads to complicated wavepacket motion withe.g. large splittings and interference. Previous experiments onsuch systems are scarce. Experimentally, femto-second pump-probe spectroscopy wasperformed using two independent optical parametric amplifiers.A near-effusive Rb2molecular beam source was developed to produce astable, high density and collision-free beam. Pump-probefluorescence was detected using an optical assembly designedfor good collection efficiency. Theoretically, analysis of experimental data was aided byquantum dynamical calculations. The used numerical simulationprogram is powerful in its ability to include any number ofstates with coupling elements, together with a fully timepropagated pump pulse-molecule interaction. It was furtherdeveloped to include molecular rotation as a centrifugalcorrection term to the potential curves, and to do statisticalthermal averaging to permit direct comparison withexperiment. Our work on the Rb2A-state system is a pioneering femto-secondexperimental curve-crossing study of a system of twointermediately coupled bound electronic states. The wavepacketfragments, following different roads, meet and interfere attheir return to the crossing. Thus, new results on theinterference properties of wavepacket dynamics in such a systemwere obtained, such as the existence of two hybrid diabatic/adiabatic trajectories, robust towards thermal averaging.Further, we show that certain scanning possibility existbetween relative contents of these two trajectories at elevatedtemperature by scanning the pump wavelength. The systemrepresents a quantum matter-wave close analogue to an opticalpulsed Michelson interferometer. The dynamics of the A-statesystem was also investigated by anisotropy measurements. Thehigh degree of signal to noise ratio obtained, revealed a newtype of small oscillatory structure, which the analysis showsoriginates from coupling between all degrees of freedom of theRb2molecule, namely electronic, vibrational androtational motion. The results of the work on the higher lying D-state systemconsist of the determination of a parallel excitationmechanism, where two wavepackets are simultaneously created intwo different electronic states. Further analysis showed thattheir future dynamics proceed essentially independently. Oneperforms adiabatic dynamics in a single‘shelf-shaped’state, while the other goes throughcurve-crossings of somewhat weaker coupling strength thanintermediate. We propose the shape of the final, unknown,pump-probe states, guided by the quantum dynamical simulationstogether with the experimental data.
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| 5. |
- Gador, Niklas, et al.
(författare)
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Dynamical interference structures in fully coupled bound-bound state quantum wave-packet dynamics
- 2004
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 70:3, s. 033418-
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Tidskriftsartikel (refereegranskat)abstract
- The quantum wave-packet dynamics in a bound-bound state system at intermediate coupling strength, the A and b states in the Rb-2 molecule coupled by spin-orbit interaction, was studied by ultrafast pump-probe molecular beam spectrocopy and quantum dynamical calculations. It was shown that even at elevated molecular temperatures the experimentally observed traces are characterized by dynamical interference structures of mesobatic, i.e., diabatic-adiabatic hybrid, kind. Two types of mesobatic motion were discerned: bistable, which occurs in both bound-unbound and bound-bound systems, and astable, which is particular to bound-bound systems at intermediate coupling strength. Contrary to previous expectations, the signatures of the quantum interference structures in pump-probe delay traces were found to be robust toward averaging over initial quantum states. It was shown that the spectral variations observed while tuning the pump pulse wavelength is a quantum matter-wave relative of the fringes observed in a pulsed optical Michelson interferometer.
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| 8. |
- Gador, Niklas, et al.
(författare)
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Molecular rotation-vibration coupling by quantum wavepacket interference at potential energy curve crossings
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 412:4-6, s. 386-390
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Tidskriftsartikel (refereegranskat)abstract
- Quantum wavepacket interference is shown to result in modulation of the ultrafast transient anisotropy of a diatomic molecule. The molecule is in a state comprising two bound electronic states at intermediate coupling strength and the anisotropy modulation enters via variations in the instantaneous contributions of the initial states to the total anisotropy. A necessary condition for the appearance of the modulation is that the involved rotational states possess different vibrational dynamics. The wavepacket interference mediates this coupling by imposing dynamical restrictions on the accessible vibrational phase space which depend on the rotational state.
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| 10. |
- Schleich, Caroline, et al.
(författare)
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Bacterial changes in a full-scale drinking water distribution system after the removal of monochloramine
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Context. Changes in drinking water treatment can affect the biofilm in the drinking water distribution system (DWDS) and enhanced monitoring is recommended to guarantee drinking water safety after substantial process modifications. Ultrafiltration was introduced in 2016 to the drinking water treatment plant Kvarnagården in Varberg, Sweden, achieving total removal of bacteria cells. This improved treatment led to the decision to remove the disinfectant monochloramine in 2020. Gap. Several studies compare the bacteria in different DWDS with and without disinfectants. To minimize complicating variables, this study examined the effects of the removal of the disinfectant in a single full scale DWDS.Aim. This study describes flow cytometry (FCM) monitoring initiated to follow bacteria in the water of the DWDS during removal of monochloramine. Methods. Water samples from 15 points in the DWDS were analysed by standard FCM, with data analysis using custom scripts in R for data analysis.Findings. By comparing FCM data to baselines, distinct changes in the bacterial community were observed following removal of monochloramine. Percentages of high nucleic acid bacteria (HNA) decreased at all sampling points, from 55 – 90 % to 45 – 60 %. Total cell counts (TCC) increased only in parts of the DWDS that had been exposed to monochloramine before the removal. Principal component analysis visualized the changes (Figure 1). The bacterial community at DWDS locations that used to differ largely regarding TCC and %HNA started to become more homogenous, emphasizing the value of FCM monitoring, as these same changes were not observed with traditional heterotrophic plate counts. The bacterial communities stabilized in summer 2020 and began to follow previously observed seasonal trends.Utilization. This study demonstrated the application of FCM monitoring of the impact of monochloramine removal on bacterial water quality, and the importance of having robust baselines for multiple locations within a DWDS for comparison.
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