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Hochlaf M, Linguerri R, Cheraki M, Ayari T, Ben Said R, Feifel R, Chambaud G. S 2O 2q+ ( q = 0, 1, and 2) Molecular Systems: Characterization and Atmospheric Planetary Implications. J Phys Chem A 2021; 125:1958-1971. [PMID: 33635674 DOI: 10.1021/acs.jpca.0c11407] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We use accurate ab initio methodologies at the coupled cluster level ((R)CCSD(T)) and its explicitly correlated version ((R)CCSD(T)-F12) to investigate the electronic structure, relative stability, and spectroscopy of the stable isomers of the [S2O2] system and of some of its cations and dications, with a special focus on the most relevant isomers that could be involved in terrestrial and planetary atmospheres. This work identifies several stable isomers (10 neutral, 8 cationic, and 5 dicationic), including trigonal-OSSO, cis-OSSO, and cyc-OSSO. For all these isomers, we calculated geometric parameters, fragmentation energies, and simple and double ionization energies of the neutral species. Several structures are identified for the first time, especially for the ionic species. Computations show that in addition to cis-OSSO and trans-OSSO proposed for the absorption in the near-UV spectrum of the Venusian atmosphere other S2O2, S2O2+, and S2O22+ species may contribute. Moreover, the characterization of the stability of singly and doubly charged S2O2 entities can also be used for their identification by mass spectrometry and UV spectroscopy in the laboratory or in planetary atmospheres. In sum, the quest for the main UV absorber in Venus' atmosphere is not over, since the physical chemistry of sulfur oxides in Venus' atmosphere is far from being understood.
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Zhong S, Vinbladh J, Busto D, Squibb RJ, Isinger M, Neoričić L, Laurell H, Weissenbilder R, Arnold CL, Feifel R, Dahlström JM, Wendin G, Gisselbrecht M, Lindroth E, L'Huillier A. Attosecond electron-spin dynamics in Xe 4d photoionization. Nat Commun 2020; 11:5042. [PMID: 33028822 PMCID: PMC7541461 DOI: 10.1038/s41467-020-18847-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Accepted: 09/09/2020] [Indexed: 11/16/2022] Open
Abstract
The photoionization of xenon atoms in the 70–100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe+ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy. A time-frequency analysis of the involved transitions allows us to identify two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as, and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as. Our results provide insight into the complex electron-spin dynamics of photo-induced phenomena. Here the authors report experiment and theory study of the photoionization of xenon inner shell 4d electron using attosecond pulses. They have identified two ionization paths - one corresponding to broad giant dipole resonance with short decay time and the other involving spin-flip transitions.
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Wituschek A, Bruder L, Allaria E, Bangert U, Binz M, Callegari C, Cinquegrana P, Danailov M, Demidovich A, Di Fraia M, Feifel R, Laarmann T, Michiels R, Mudrich M, Nikolov I, Piseri P, Plekan O, Charles Prince K, Przystawik A, Rebernic Ribič P, Sigalotti P, Stranges S, Uhl D, Giannessi L, Stienkemeier F. High-gain harmonic generation with temporally overlapping seed pulses and application to ultrafast spectroscopy. OPTICS EXPRESS 2020; 28:29976-29990. [PMID: 33114885 DOI: 10.1364/oe.401249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Accepted: 09/07/2020] [Indexed: 06/11/2023]
Abstract
Collinear double-pulse seeding of the High-Gain Harmonic Generation (HGHG) process in a free-electron laser (FEL) is a promising approach to facilitate various coherent nonlinear spectroscopy schemes in the extreme ultraviolet (XUV) spectral range. However, in collinear arrangements using a single nonlinear medium, temporally overlapping seed pulses may introduce nonlinear mixing signals that compromise the experiment at short time delays. Here, we investigate these effects in detail by extending the analysis described in a recent publication (Wituschek et al., Nat. Commun., 11, 883, 2020). High-order fringe-resolved autocorrelation and wave packet interferometry experiments at photon energies > 23 eV are performed, accompanied by numerical simulations. It turns out that both the autocorrelation and the wave-packet interferometry data are very sensitive to saturation effects and can thus be used to characterize saturation in the HGHG process. Our results further imply that time-resolved spectroscopy experiments are feasible even for time delays smaller than the seed pulse duration.
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Nandi S, Plésiat E, Zhong S, Palacios A, Busto D, Isinger M, Neoričić L, Arnold CL, Squibb RJ, Feifel R, Decleva P, L’Huillier A, Martín F, Gisselbrecht M. Attosecond timing of electron emission from a molecular shape resonance. SCIENCE ADVANCES 2020; 6:eaba7762. [PMID: 32789174 PMCID: PMC7399650 DOI: 10.1126/sciadv.aba7762] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2020] [Accepted: 06/17/2020] [Indexed: 06/11/2023]
Abstract
Shape resonances in physics and chemistry arise from the spatial confinement of a particle by a potential barrier. In molecular photoionization, these barriers prevent the electron from escaping instantaneously, so that nuclei may move and modify the potential, thereby affecting the ionization process. By using an attosecond two-color interferometric approach in combination with high spectral resolution, we have captured the changes induced by the nuclear motion on the centrifugal barrier that sustains the well-known shape resonance in valence-ionized N2. We show that despite the nuclear motion altering the bond length by only 2%, which leads to tiny changes in the potential barrier, the corresponding change in the ionization time can be as large as 200 attoseconds. This result poses limits to the concept of instantaneous electronic transitions in molecules, which is at the basis of the Franck-Condon principle of molecular spectroscopy.
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Maroju PK, Grazioli C, Di Fraia M, Moioli M, Ertel D, Ahmadi H, Plekan O, Finetti P, Allaria E, Giannessi L, De Ninno G, Spezzani C, Penco G, Spampinati S, Demidovich A, Danailov MB, Borghes R, Kourousias G, Sanches Dos Reis CE, Billé F, Lutman AA, Squibb RJ, Feifel R, Carpeggiani P, Reduzzi M, Mazza T, Meyer M, Bengtsson S, Ibrakovic N, Simpson ER, Mauritsson J, Csizmadia T, Dumergue M, Kühn S, Nandiga Gopalakrishna H, You D, Ueda K, Labeye M, Bækhøj JE, Schafer KJ, Gryzlova EV, Grum-Grzhimailo AN, Prince KC, Callegari C, Sansone G. Attosecond pulse shaping using a seeded free-electron laser. Nature 2020; 578:386-391. [DOI: 10.1038/s41586-020-2005-6] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 11/05/2019] [Indexed: 11/09/2022]
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Wallner M, Eland JHD, Squibb RJ, Andersson J, Roos AH, Singh R, Talaee O, Koulentianos D, Piancastelli MN, Simon M, Feifel R. Coulomb explosion of CD 3I induced by single photon deep inner-shell ionisation. Sci Rep 2020; 10:1246. [PMID: 31988321 PMCID: PMC6985119 DOI: 10.1038/s41598-020-58251-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 01/13/2020] [Indexed: 12/05/2022] Open
Abstract
L-shell ionisation and subsequent Coulomb explosion of fully deuterated methyl iodide, CD3I, irradiated with hard X-rays has been examined by a time-of-flight multi-ion coincidence technique. The core vacancies relax efficiently by Auger cascades, leading to charge states up to 16+. The dynamics of the Coulomb explosion process are investigated by calculating the ions’ flight times numerically based on a geometric model of the experimental apparatus, for comparison with the experimental data. A parametric model of the explosion, previously introduced for multi-photon induced Coulomb explosion, is applied in numerical simulations, giving good agreement with the experimental results for medium charge states. Deviations for higher charges suggest the need to include nuclear motion in a putatively more complete model. Detection efficiency corrections from the simulations are used to determine the true distributions of molecular charge states produced by initial L1, L2 and L3 ionisation.
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Andersson J, Zagorodskikh S, Roos AH, Talaee O, Squibb RJ, Koulentianos D, Wallner M, Zhaunerchyk V, Singh R, Eland JHD, Rost JM, Feifel R. Parametrization of energy sharing distributions in direct double photoionization of He. Sci Rep 2019; 9:17883. [PMID: 31784628 PMCID: PMC6884530 DOI: 10.1038/s41598-019-53545-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Accepted: 10/31/2019] [Indexed: 11/18/2022] Open
Abstract
We present experimental results on the characteristic sharing of available excess energy, ranging from 11–221 eV, between two electrons in single-photon direct double ionization of He. An effective parametrization of the sharing distributions is presented along with an empirical model that describes the complete shape of the distribution based on a single experimentally determinable parameter. The measured total energy sharing distributions are separated into two distributions representing the shake-off and knock-out parts by simulating the sharing distribution curves expected from a pure wave collapse after a sudden removal of the primary electron. In this way, empirical knock-out distributions are extracted and both the shake-off and knock-out distributions are parametrized. These results suggest a simple method that can be applied to other atomic and molecular systems to experimentally study important aspects of the direct double ionization process.
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Eland JHD, Feifel R. Triple ionization of HCl via states with a 2p core hole. J Chem Phys 2019; 151:114301. [PMID: 31542004 DOI: 10.1063/1.5115552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The triple ionization of HCl by double Auger decay and related processes has been studied using a multiparticle coincidence technique combined with synchrotron radiation. Four contributing processes are identified; direct double Auger, two indirect double Auger decay pathways, and single Auger decay from core-valence doubly ionized intermediate states. One indirect Auger process involves autoionization from superexcited states of Cl+. Double Auger decay from HCl+ (2p-1, 2PJ), which makes up 11% ± 2% of total Auger decay, is estimated to be 40% direct, 15% indirect via atomic Cl+* and 45% indirect via molecular intermediate doubly ionized states. The vertical triple ionization energy of HCl is determined as 73.8 ± 0.5 eV. Molecular field effects are found to affect the direct double Auger process as well as normal single Auger decay. A comparison between spectra of the HCl and DCl isotopomers indicates that electronic decay is faster in all the processes than molecular dissociation.
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Yatsyna V, Mallat R, Gorn T, Schmitt M, Feifel R, Rijs AM, Zhaunerchyk V. Conformational Preferences of Isolated Glycylglycine (Gly-Gly) Investigated with IRMPD-VUV Action Spectroscopy and Advanced Computational Approaches. J Phys Chem A 2019; 123:862-872. [DOI: 10.1021/acs.jpca.8b10881] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Hult Roos A, Eland JHD, Andersson J, Wallner M, Squibb RJ, Feifel R. Relative extent of triple Auger decay in CO and CO2. Phys Chem Chem Phys 2019; 21:9889-9894. [DOI: 10.1039/c9cp01415b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Systematic measurements on single and triple Auger decay in CO and CO2 after the creation of a C 1s or a O 1s core vacancy show that the percentage of triple Auger decay is on the order of 10−2 of the single Auger decay in these molecules.
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Yatsyna V, Mallat R, Gorn T, Schmitt M, Feifel R, Rijs AM, Zhaunerchyk V. Competition between folded and extended structures of alanylalanine (Ala-Ala) in a molecular beam. Phys Chem Chem Phys 2019; 21:14126-14132. [DOI: 10.1039/c9cp00140a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Structural analysis of the neutral dipeptide Ala-Ala by action spectroscopy using IRMPD-VUV spectroscopy reveals predominance of extended structure.
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Roos AH, Eland JHD, Andersson J, Squibb RJ, Feifel R. Dissociations of water ions after valence and inner-valence ionization. J Chem Phys 2018; 149:204307. [DOI: 10.1063/1.5055593] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
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Koulentianos D, Carniato S, Püttner R, Goldsztejn G, Marchenko T, Travnikova O, Journel L, Guillemin R, Céolin D, Rocco MLM, Piancastelli MN, Feifel R, Simon M. Double-core-hole states in CH3CN: Pre-edge structures and chemical-shift contributions. J Chem Phys 2018; 149:134313. [DOI: 10.1063/1.5047854] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Roos AH, Eland JHD, Andersson J, Zagorodskikh S, Singh R, Squibb RJ, Feifel R. Relative extent of double and single Auger decay in molecules containing C, N and O atoms. Phys Chem Chem Phys 2018; 18:25705-25710. [PMID: 27711372 DOI: 10.1039/c6cp02414a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
We show that the proportion of double Auger decay following creation of single 1s core holes in molecules containing C, N and O atoms is greater than usually assumed, amounting to about 10% of single Auger decay in many cases. It varies from molecule to molecule, where the size of the molecule has a positive correlation to the amount of double Auger decay. In neon, examined as a related benchmark, the proportion of double Auger decay is similar to that in methane, and is in the order of 5%.
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Squibb RJ, Sapunar M, Ponzi A, Richter R, Kivimäki A, Plekan O, Finetti P, Sisourat N, Zhaunerchyk V, Marchenko T, Journel L, Guillemin R, Cucini R, Coreno M, Grazioli C, Di Fraia M, Callegari C, Prince KC, Decleva P, Simon M, Eland JHD, Došlić N, Feifel R, Piancastelli MN. Acetylacetone photodynamics at a seeded free-electron laser. Nat Commun 2018; 9:63. [PMID: 29302026 PMCID: PMC5754354 DOI: 10.1038/s41467-017-02478-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Accepted: 12/04/2017] [Indexed: 11/30/2022] Open
Abstract
The first steps in photochemical processes, such as photosynthesis or animal vision, involve changes in electronic and geometric structure on extremely short time scales. Time-resolved photoelectron spectroscopy is a natural way to measure such changes, but has been hindered hitherto by limitations of available pulsed light sources in the vacuum-ultraviolet and soft X-ray spectral region, which have insufficient resolution in time and energy simultaneously. The unique combination of intensity, energy resolution, and femtosecond pulse duration of the FERMI-seeded free-electron laser can now provide exceptionally detailed information on photoexcitation–deexcitation and fragmentation in pump-probe experiments on the 50-femtosecond time scale. For the prototypical system acetylacetone we report here electron spectra measured as a function of time delay with enough spectral and time resolution to follow several photoexcited species through well-characterized individual steps, interpreted using state-of-the-art static and dynamics calculations. These results open the way for investigations of photochemical processes in unprecedented detail. The first steps in photochemical processes involve changes in electronic and geometric structure on extremely short timescales. Here, the authors report femtosecond dynamics in prototypical acetylacetone, by pump-probe photoexcitation-photoemission experiments and static and dynamics calculations.
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Koulentianos D, Püttner R, Goldsztejn G, Marchenko T, Travnikova O, Journel L, Guillemin R, Céolin D, Piancastelli MN, Simon M, Feifel R. KL double core hole pre-edge states of HCl. Phys Chem Chem Phys 2018; 20:2724-2730. [DOI: 10.1039/c7cp04214k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The formation of double core hole pre-edge states of the form 1s−12p−1(1,3P)σ*,n for HCl, located on the binding energy scale as deep as 3 keV, has been investigated by means of a high resolution single channel electron spectroscopy technique recently developed for the hard X-ray region.
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Isinger M, Squibb RJ, Busto D, Zhong S, Harth A, Kroon D, Nandi S, Arnold CL, Miranda M, Dahlström JM, Lindroth E, Feifel R, Gisselbrecht M, L’Huillier A. Photoionization in the time and frequency domain. Science 2017; 358:893-896. [DOI: 10.1126/science.aao7043] [Citation(s) in RCA: 141] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 10/19/2017] [Indexed: 11/02/2022]
Abstract
Ultrafast processes in matter, such as the electron emission after light absorption, can now be studied using ultrashort light pulses of attosecond duration (10−18 seconds) in the extreme ultraviolet spectral range. The lack of spectral resolution due to the use of short light pulses has raised issues in the interpretation of the experimental results and the comparison with theoretical calculations. We determine photoionization time delays in neon atoms over a 40–electron volt energy range with an interferometric technique combining high temporal and spectral resolution. We spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations, thereby solving a puzzle raised by 7-year-old measurements.
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Feifel R, Eland JHD, Carniato S, Selles P, Püttner R, Koulentianos D, Marchenko T, Journel L, Guillemin R, Goldsztejn G, Travnikova O, Ismail I, Miranda BCD, Lago AF, Céolin D, Lablanquie P, Penent F, Piancastelli MN, Simon M. Cationic double K-hole pre-edge states of CS 2 and SF 6. Sci Rep 2017; 7:13317. [PMID: 29042664 PMCID: PMC5645408 DOI: 10.1038/s41598-017-13607-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Accepted: 09/26/2017] [Indexed: 11/09/2022] Open
Abstract
Recent advances in X-ray instrumentation have made it possible to measure the spectra of an essentially unexplored class of electronic states associated with double inner-shell vacancies. Using the technique of single electron spectroscopy, spectra of states in CS2 and SF6 with a double hole in the K-shell and one electron exited to a normally unoccupied orbital have been obtained. The spectra are interpreted with the aid of a high-level theoretical model giving excellent agreement with the experiment. The results shed new light on the important distinction between direct and conjugate shake-up in a molecular context. In particular, systematic similarities and differences between pre-edge states near single core holes investigated in X-ray absorption spectra and the corresponding states near double core holes studied here are brought out.
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Hult Roos A, Eland J, Koulentianos D, Squibb R, Karlsson L, Feifel R. Valence double ionization electron spectra of CH 3 F, CH 3 Cl and CH 3 I. Chem Phys 2017. [DOI: 10.1016/j.chemphys.2017.04.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Wolf TJA, Myhre RH, Cryan JP, Coriani S, Squibb RJ, Battistoni A, Berrah N, Bostedt C, Bucksbaum P, Coslovich G, Feifel R, Gaffney KJ, Grilj J, Martinez TJ, Miyabe S, Moeller SP, Mucke M, Natan A, Obaid R, Osipov T, Plekan O, Wang S, Koch H, Gühr M. Probing ultrafast ππ*/nπ* internal conversion in organic chromophores via K-edge resonant absorption. Nat Commun 2017; 8:29. [PMID: 28642477 PMCID: PMC5481431 DOI: 10.1038/s41467-017-00069-7] [Citation(s) in RCA: 105] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 04/28/2017] [Indexed: 11/09/2022] Open
Abstract
Many photoinduced processes including photosynthesis and human vision happen in organic molecules and involve coupled femtosecond dynamics of nuclei and electrons. Organic molecules with heteroatoms often possess an important excited-state relaxation channel from an optically allowed ππ* to a dark nπ* state. The ππ*/nπ* internal conversion is difficult to investigate, as most spectroscopic methods are not exclusively sensitive to changes in the excited-state electronic structure. Here, we report achieving the required sensitivity by exploiting the element and site specificity of near-edge soft X-ray absorption spectroscopy. As a hole forms in the n orbital during ππ*/nπ* internal conversion, the absorption spectrum at the heteroatom K-edge exhibits an additional resonance. We demonstrate the concept using the nucleobase thymine at the oxygen K-edge, and unambiguously show that ππ*/nπ* internal conversion takes place within (60 ± 30) fs. High-level-coupled cluster calculations confirm the method's impressive electronic structure sensitivity for excited-state investigations.Many photo-induced processes such as photosynthesis occur in organic molecules, but their femtosecond excited-state dynamics are difficult to track. Here, the authors exploit the element and site selectivity of soft X-ray absorption to sensitively follow the ultrafast ππ*/nπ* electronic relaxation of hetero-organic molecules.
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Sanchez-Gonzalez A, Micaelli P, Olivier C, Barillot TR, Ilchen M, Lutman AA, Marinelli A, Maxwell T, Achner A, Agåker M, Berrah N, Bostedt C, Bozek JD, Buck J, Bucksbaum PH, Montero SC, Cooper B, Cryan JP, Dong M, Feifel R, Frasinski LJ, Fukuzawa H, Galler A, Hartmann G, Hartmann N, Helml W, Johnson AS, Knie A, Lindahl AO, Liu J, Motomura K, Mucke M, O'Grady C, Rubensson JE, Simpson ER, Squibb RJ, Såthe C, Ueda K, Vacher M, Walke DJ, Zhaunerchyk V, Coffee RN, Marangos JP. Accurate prediction of X-ray pulse properties from a free-electron laser using machine learning. Nat Commun 2017; 8:15461. [PMID: 28580940 PMCID: PMC5465316 DOI: 10.1038/ncomms15461] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 03/30/2017] [Indexed: 11/09/2022] Open
Abstract
Free-electron lasers providing ultra-short high-brightness pulses of X-ray radiation have great potential for a wide impact on science, and are a critical element for unravelling the structural dynamics of matter. To fully harness this potential, we must accurately know the X-ray properties: intensity, spectrum and temporal profile. Owing to the inherent fluctuations in free-electron lasers, this mandates a full characterization of the properties for each and every pulse. While diagnostics of these properties exist, they are often invasive and many cannot operate at a high-repetition rate. Here, we present a technique for circumventing this limitation. Employing a machine learning strategy, we can accurately predict X-ray properties for every shot using only parameters that are easily recorded at high-repetition rate, by training a model on a small set of fully diagnosed pulses. This opens the door to fully realizing the promise of next-generation high-repetition rate X-ray lasers.
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Yatsyna V, Bakker DJ, Feifel R, Rijs AM, Zhaunerchyk V. Far-infrared amide IV-VI spectroscopy of isolated 2- and 4-Methylacetanilide. J Chem Phys 2017; 145:104309. [PMID: 27634262 DOI: 10.1063/1.4962360] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Delocalized molecular vibrations in the far-infrared and THz ranges are highly sensitive to the molecular structure, as well as to intra- and inter-molecular interactions. Thus, spectroscopic studies of biomolecular structures can greatly benefit from an extension of the conventional mid-infrared to the far-infrared wavelength range. In this work, the conformer-specific gas-phase far-infrared spectra of two aromatic molecules containing the peptide -CO-NH- link, namely, 2- and 4-Methylacetanilide, are investigated. The planar conformations with trans configuration of the peptide link have only been observed in the supersonic-jet expansion. The corresponding far-infrared signatures associated with the vibrations of the peptide -CO-NH- moiety, the so-called amide IV-VI bands, have been assigned and compared with the results of density functional theory frequency calculations based on the anharmonic vibrational second-order perturbation theory approach. The analysis of the experimental and theoretical data shows that the amide IV-VI bands are highly diagnostic for the geometry of the peptide moiety and the molecular backbone. They are also strongly blue-shifted upon formation of the NH⋯O-C hydrogen bonding, which is, for example, responsible for the formation of secondary protein structures. Furthermore, the amide IV-VI bands are also diagnostic for the cis configuration of the peptide link, which can be present in cyclic peptides. The experimental gas-phase data presented in this work can assist the vibrational assignment of similar biologically important systems, either isolated or in natural environments.
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Hansen K, Richter R, Alagia M, Stranges S, Schio L, Salén P, Yatsyna V, Feifel R, Zhaunerchyk V. Single Photon Thermal Ionization of C_{60}. PHYSICAL REVIEW LETTERS 2017; 118:103001. [PMID: 28339240 DOI: 10.1103/physrevlett.118.103001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Indexed: 06/06/2023]
Abstract
We report on experiments which show that C_{60} can ionize in an indirect, quasithermal boiloff process after absorption of a single photon. The process involves a large number of incoherently excited valence electrons and yields electron spectra with a Boltzmann distribution with temperatures exceeding 10^{4} K. It is expected to be present for other molecules and clusters with a comparatively large number of valence electrons. The astrophysical consequences are briefly discussed.
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Zagorodskikh S, Eland JHD, Zhaunerchyk V, Mucke M, Squibb RJ, Linusson P, Feifel R. Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal). J Chem Phys 2016; 145:124302. [DOI: 10.1063/1.4962823] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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