| 1. |
- 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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| 2. |
- Ernst, Hanna A., et al.
(författare)
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Ultrafast Dynamics of o-Nitrophenol : An Experimental and Theoretical Study
- 2015
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 119:35, s. 9225-9235
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Tidskriftsartikel (refereegranskat)abstract
- The photolysis of o-nitrophenol (o-NP), a typical push pull molecule, is of current interest in atmospheric chemistry as a possible source of nitrous acid (HONO). To characterize the largely unknown photolysis mechanism, the dynamics of the lowest lying excited singlet state (S-1) of o-NP was investigated by means of femtosecond transient absorption spectroscopy in solution, time-resolved photoelectron spectroscopy (TRPES) in the gas phase and quantum chemical calculations. Evidence of the unstable aci-nitro isomer is provided both in the liquid and in the gas phase. Our results indicate that the Si state displays strong charge transfer character, which triggers excited state proton transfer from the OH to the NO2 group as evidenced by a temporal shift of 20 fs of the onset of the photoelectron spectrum. The proton transfer itself is found to be coupled to an out-of-plane rotation of the newly formed HONO group, finally leading to a conical intersection between Si and the ground state So. In solution, return to So within 0.2-0.3 ps was monitored by stimulated emission. As a competitive relaxation channel, ultrafast intersystem crossing to the upper triplet manifold on a subpicosecond time scale occurs both in solution and in the gas phase. Due to the ultrafast singlet dynamics, we conclude that the much discussed HONO split-off is likely to take place in the triplet manifold.
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| 3. |
- Glover, William J., et al.
(författare)
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Excited state non-adiabatic dynamics of the smallest polyene, trans 1,3-butadiene. II. Ab initio multiple spawning simulations
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:16
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Tidskriftsartikel (refereegranskat)abstract
- The excited state non-adiabatic dynamics of the smallest polyene, trans 1,3-butadiene (BD), has long been the subject of controversy due to its strong coupling, ultrafast time scales and the difficulties that theory faces in describing the relevant electronic states in a balanced fashion. Here we apply Ab Initio Multiple Spawning (AIMS) using state-averaged complete active space multistate second order perturbation theory [SA-3-CAS(4/4)-MSPT2] which describes both static and dynamic electron correlation effects, providing a balanced description of both the initially prepared bright 1(1)B(u) (pi pi*) state and non-adiabatically coupled dark 2(1)A(g) state of BD. Importantly, AIMS allows for on-the-fly calculations of experimental observables. We validate our approach by directly simulating the time resolved photoelectron-photoion coincidence spectroscopy results presented in Paper I [A. E. Boguslavskiy et al., J. Chem. Phys. 148, 164302 (2018)], demonstrating excellent agreement with experiment. Our simulations reveal that the initial excitation to the 11Bu state rapidly evolves via wavepacket dynamics that follow both bright-and dark-state pathways as well as mixtures of these. In order to test the sensitivity of the AIMS results to the relative ordering of states, we considered two hypothetical scenarios biased toward either the bright B-1(u) or the dark 2(1)A(g) state. In contrast with AIMS/SA-3-CAS(4/4)-MSPT2 simulations, neither of these scenarios yields favorable agreement with experiment. Thus, we conclude that the excited state non-adiabatic dynamics in BD involves both of these ultrafast pathways.
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| 4. |
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| 5. |
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| 6. |
- Schalk, Oliver, et al.
(författare)
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Internal Conversion versus Intersystem Crossing : What Drives the Gas Phase Dynamics of Cyclic alpha,beta-Enones?
- 2014
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:12, s. 2279-2287
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the competition between intersystem crossing (ISC) and internal conversion (IC) as nonradiative relaxation pathways in cyclic alpha,beta-unsaturated enones following excitation to their lowest lying (1)pi pi* state, by means of time-resolved photoelectron spectroscopy and ab initio computation. Upon excitation, the (1)pi pi* state of 2-cyclopentenone decays to the lowest lying (1)pi pi* state within 120 +/- 20 fs. Within 1.2 +/- 0.2 ps, the molecule subsequently decays to the triplet manifold and the singlet ground state, with quantum yields of 0.35 and 0.65, respectively. The corresponding dynamics in modified derivatives, obtained by selective methylation, show a decrease in both IC and ISC rates, with the quantum yields of ISC varying between 0.35 and 0.08. The rapid rates of ISC are explained by a large spin orbit coupling of 45-60 cm(-1) over an extended region of near degeneracy between the singlet and triplet state. Furthermore, the rate of IC is depressed by the existence of a well-defined minimum on the (1)n pi* potential energy surface. The nonadiabatic pathways evinced by the present results highlight the fact that these molecular systems conceptually represent "intermediate cases" between ultrafast dynamics mediated by vibrational motions at conical intersections versus those by statistical decay mechanisms.
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| 7. |
- Schalk, Oliver, et al.
(författare)
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On the Condensed Phase Ring-Closure of Vinylheptafulvalene and Ring-Opening of Gaseous Dihydroazulene
- 2013
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 117:16, s. 3340-3347
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Tidskriftsartikel (refereegranskat)abstract
- Dihydroazulenes are interesting because of their photoswitching behavior. While the ring-opening to vinylheptafulvalene (VHF) is light induced, the back reaction is known to proceed thermally. In the present paper, we show the first gas phase study of the ring-opening reaction of 2-phenyl-1,8a-dihydroazulene-1,1-dicarbonitrile (Ph-DHA) by means of time-resolved photoelectron spectroscopy which permits us to follow the ring-opening process. Moreover, we investigated s-trans-Ph-VHF in a series of transient absorption experiments, supported by ab initio computations, to understand the origin of the absence of light-induced ring-closure. The transient absorption results show a biexponential decay governed by a hitherto unknown state. This state is accessed within 1-2 ps and return to the ground state is probably driven through a cis-trans isomerization about the exocyclic C-1=C-2 double bond. The rapid decrease in potential energy disfavors internal rotation to s-cis-Ph-VHF, the structure that would precede the ring-closure reaction.
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| 8. |
- Schalk, Oliver, et al.
(författare)
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Substituent Effects on Dynamics at Conical Intersections : Cycloheptatrienes
- 2013
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 117:40, s. 10239-10247
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Tidskriftsartikel (refereegranskat)abstract
- Using selective methyl substitution, we study the effects of vibrational dynamics at conical intersections in unsaturated hydrocarbons. Here, we investigate the excited state nonadiabatic dynamics of cycloheptatriene (CHT) and its relation to dynamics in other polyenes by comparing CHT with 7-methyl CHT, 7-ethyl CHT, and perdeuterated CHT using time-resolved photoelectron spectroscopy and photoelectron anisotropy. Our results suggest that, upon pi pi*-excitation to the bright 2A state, we observe an early intersection with the dark 2A' state close to the Franck-Condon region with evidence of wavepacket bifurcation. This indicates that the wavepacket evolves on both states, likely along a planarization coordinate, with the majority of the flux undergoing nonadiabatic transition via conical intersections within 100 fs following light absorption. In CHT, large amplitude motion along the planarization coordinate improves the intra-ring pi-overlap, yielding a delocalized electronic density. However, substitutions in 7 position, chosen to modify the inertia of the planarization motion, did not markedly alter the first step in the sequential kinetic scheme. This suggests that there is a crossing of potential energy surfaces before planarization is achieved and, thus, nonadiabatic transition likely takes place far away from a local minimum.
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| 9. |
- Schalk, Oliver, et al.
(författare)
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Time-resolved photoelectron spectroscopy of nitrobenzene and its aldehydes
- 2018
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 691, s. 379-387
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Tidskriftsartikel (refereegranskat)abstract
- We report the first femtosecond time-resolved photoelectron spectroscopy study of 2-, 3-and 4-nitrobenzaldehyde (NBA) and nitrobenzene (NBE) in the gas phase upon excitation at 200 nm. In 3- and 4-NBA, the dynamics follow fast intersystem crossing within 1-2 picoseconds. In 2-NBA and NBE, the dynamics are faster (similar to 0.5 ps). 2-NBA undergoes hydrogen transfer similar to solution phase dynamics. NBE either releases NO2 in the excited state or converts internally back to the ground state. We discuss why these channels are suppressed in the other nitrobenzaldehydes.
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| 10. |
- Schalk, Oliver, et al.
(författare)
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Two-Photon Excited State Dynamics of Dark Valence, Rydberg, and Superexcited States in 1,3-Butadiene
- 2014
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 5:3, s. 560-565
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Tidskriftsartikel (refereegranskat)abstract
- Two-photon absorption in systems with parity permits access to states that cannot be prepared by one-photon absorption. Here we present the first time-resolved photoelectron spectroscopy study using this technique, applied to 1,3-butadiene, in which we investigated the dynamics of its dark valence, Rydberg, and superexcited states. The dark valence state dynamics are accessed via the Rydberg manifold, excited by two photons of 400 nm. We find that the 'dark' 2(1)A(g) state populated in this manner has a much longer lifetime than when accesses via the 1(1)B(u) 'bright' valence state when populated by one photon of 200 nm. In addition, we compared the dynamics of the 3s pi- and 3d pi-Rydberg states. These Rydberg states relax to the valence manifold on a subpicosecond time scale, with the 3s pi-Rydberg state decay rate being larger due to a stronger valence-Rydberg mixing. Finally, we investigated superexcited valence states that fragment or autoionize within 200 fs, likely without involving Rydberg states.
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