Ultrafast Nonadiabatic Cascade and Subsequent Photofragmentation

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Spectroscopy and Photochemistry; General Theory

Ultrafast Nonadiabatic Cascade and Subsequent Photofragmentation of Extreme Ultraviolet Excited Caffeine Molecule Alexandre Marciniak, Kaoru Yamazaki, Satoshi Maeda, Maurizio Reduzzi, Victor Despré, Marius Hervé, Mehdi Meziane, Thomas A. Niehaus, Vincent Loriot, Alexander I. Kuleff, Baptiste Schindler, Isabelle Compagnon, Guiseppe Sansone, and Franck Lepine J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b02964 • Publication Date (Web): 16 Nov 2018 Downloaded from http://pubs.acs.org on November 19, 2018

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The Journal of Physical Chemistry Letters

Ultrafast Nonadiabatic Cascade and Subsequent Photofragmentation of Extreme Ultraviolet Excited Caffeine Molecule Alexandre Marciniak1, Kaoru Yamazaki2, Satoshi Maeda3, Maurizio Reduzzi4, Victor Despré1, Marius Hervé1, Mehdi Meziane1, Thomas A. Niehaus1, Vincent Loriot1, Alexander I. Kuleff6, Baptiste Schindler1, Isabelle Compagnon1,8, Guiseppe Sansone4,5 and Franck Lépine1 AUTHOR ADDRESS 1

Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622, VILLEURBANNE, France 2

Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

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Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan 4

Dipartimento di Fisica, Politecnico Piazza, Leonardo da Vinci 32, 20133 Milan, Italy

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Physikalisches Institute Albert-Ludwigs-Universität Freiburg, Stefan Meier Straße 19, D79104 Freiburg, Germany 6

Theoretische Chemie, PCI, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany 7 8

ELI-ALPS, Budapesti út 5, H-6728 Szeged, Hungary Institut Universitaire de France IUF, 103 Blvd St. Michel, F-75005 Paris, France

Corresponding Authors [email protected] [email protected]

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The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Ultrafast XUV-chemistry is offering new opportunities to decipher the complex dynamics taking place in highly excited molecular states and thus better understand fundamental natural phenomena as molecule formation in interstellar media. We used ultrashort XUV light pulses to perform XUV-pump–IR-probe experiments in caffeine as a model of prebiotic molecule. We observed a 40-fs decay of excited cationic states. Guided by quantum calculations, this timescale is interpreted in terms of a non-adiabatic cascade through a large number of highly correlated states. This shows that the correlation driven non-adiabatic relaxation seems to be a general process for highly excited states, which might impact our understanding of molecular processing in interstellar media. TOC figure

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In the past decade there has been a rising interest for understanding ultrafast photoinduced molecular dynamics following XUV excitation. This growing attention follows the new technical abilities to temporally resolve processes on femtosecond or even attosecond timescales using emerging light sources that provide ultrashort XUV pulses1,2,3,4. In molecules, ultrafast photo-induced reactions are governed by microscopic quantum processes that are determined by the complex interplay between light and constituting particles (electrons and nuclei). At the early age of femtochemistry, such effects were investigated by measuring picosecond radiationless relaxations of ultraviolet (UV) excited DNA bases showing that nonadiabatic couplings between electronic and nuclear degrees of freedom were responsible for the photostability of biomolecules which insures life persistence 5 , 6 . These pioneering works investigated the nonradiative relaxation of the first electronically excited states through conical intersections (CIs) which are crossings between adiabatic potential energy hypersurfaces corresponding to sets of molecular geometries at which the electronic and nuclear degrees of freedom are strongly coupled7,8. When dealing with higher excitation energies, the excitation scheme and relaxation mechanisms are much more puzzling as they involve a large number of states and various decay channels that make the interpretation very challenging. Moreover, very rarely these states correspond to one-electron transitions. Instead, due to the electron correlation, they have a many-body nature9. Therefore, exposing molecules to ultrashort energetic pulses (such as extreme ultraviolet (XUV) ultrashort pulses) can lead to new intriguing phenomena, such as coherent electronic dynamics 10 ,11 or hole migration driven by electron correlation 12 ’ 13 , where a charge can oscillate across the molecular backbone within a few fs even at frozen nuclear geometry.

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Highly excited species take part in many natural processes such as combustion, radiation damage14, or in the chemistry occurring in molecular clouds of interstellar media15. This has motivated the recent investigation of ultrafast XUV-photochemistry of PAH (polycyclic aromatic hydrocarbons)16. First experiments have demonstrated the existence of unexpected lifetimes in excited PAH cationic states which can be interpreted through complex many-body quantum effects in which the highly correlated electronic states play a major role17. These effects can be important to unravel the chemistry of interstellar media. In this respect, it is important to understand which class of molecules are mostly affected by such mechanisms. In this article, we have pushed these experiments one step further by investigating the dynamics of XUV-excited caffeine molecules, which is relevant for both astrochemistry and biophysics. Indeed, caffeine consists of a purine backbone (see Fig. S2) which is also the basis for many other prebiotic building blocks such as adenine, guanine or xanthine that have been detected in carbonaceous meteorites18 suggesting that they have been synthesized in the early age of the solar system, where they are processed by XUV radiation. Besides, caffeine molecules have been investigated in UV transient absorption spectroscopy in liquid phase by Chen and Kohler19 demonstrating the existence of a 500 fs nonradiative decay mechanism which may involve CI accessed via out-of-plane deformations of caffeine. In our study, we performed XUV pump-IR probe measurements in neutral caffeine produced in gas phase. We resolved the dynamics induced by the XUV excitation on the femtosecond timescale allowing to extract ultrafast relaxation dynamics of a few tens of fs through specific fragmentation channels of the caffeine cation. This timescale is understood in terms of an internal conversion (IC) cascade through a large density of states that is probed by IR photoexcitation

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of the unstable dications that dissociate. This interpretation is supported by quantum chemistry calculations. The experiment has been performed using an XUV-IR pump-probe set-up with attosecond resolution20 (see SI). The output of an amplified laser system delivering 25 fs (λ0 = 800 nm), 2 mJ per pulse at 10 kHz repetition rate, is injected in a hollow fiber to be spectrally broadened and recompressed leading to 1 mJ, 6 fs pulses. The beam is split in two parts, 90% is used to be focused on a gas cell to generate high harmonics. The XUV light is filtered using metallic foils (Al, Sn or In 200 nm thickness) and finally recombined with the second part (10%) of the IR beam using a holed mirror. Both beams are then focused in the interaction chamber where they cross the molecular beam at the center of the velocity map imaging spectrometer used in ion time-of-flight mode, while the electron velocity mode is used for laser beams alignment and characterization purposes. The cross-correlation between the XUV and IR beam was estimated to be 25 fs. The neutral caffeine is obtained in the gas phase by sublimation (150 °C) of a solid sample. The central photon energy for HHG in xenon is around 25 eV (see Fig. S1 in SI). A typical XUV photo-ion ratio spectrum is shown in Fig. 1 where the yield ratios correspond to the fragment yield divided by the sum over all the ionic species coming from the neutral caffeine. We can observe that caffeine cation is produced, and the predominant fragments are m/q = 109 (F109), m/q = 82 (F82) and m/q = 67 (F67). The main fragmentation channel is the production of F109 that subsequently dissociates into F82 and F6727. Changing the central XUV photon energy to 31 eV (by changing the HHG gas to krypton), opens up new fragmentation channels, creating smaller fragments (m/q < 60). This increases the small yield ratio (for instance it increases the yield ratio of CH3+ fragment by four time) and depletes the main fragment ratio, suggesting that the increase of the internal energy leads to a sequential 5



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dissociation (see Fig. S3). In the following, we have investigated how this fragmentation pattern evolves on a femtosecond timescale, using the XUV pump-IR probe scheme. To resolve the underlying dynamics following XUV photoionization, the variation of the ion yield is measured as a function of the XUV-IR pump-probe delay from -50 to 250 fs. We consider the two-color ion yield corresponding to the signal that depends on both laser pulses. It is defined as the total signal from which we have subtracted the one obtained in XUV-only and the one obtained in IR–only measurements: ∆𝑆(𝑡) = 𝑆XUV+IR (𝑡) − 𝑆XUV only − 𝑆IR only

(1)

Thus, we can follow the evolution of the two-color ion yields as a function of the pump-probe delay and a 3D map of this evolution is shown in Fig. 2. We clearly observe that some fragments, such as CH3+ (m/q = 15) or C5N3H7+ (m/q = 109), display transient ultrafast variations evolving in a few tens of fs. Moreover, in Fig. 2 we can distinguish two types of transient dynamics: a transient population (positive signal) and a transient depopulation (negative signal). The first kind of dynamics is mainly present in small fragments: CH3+ (m/q = 15), CO+ (28), H3CN+ (29), NCN+ (40), NCHN+ (41), H3CNCH+ or OCN+(42), NCHNCH3+ (56), F58. The second one (depletion), is mainly present in bigger fragments: caffeine losing CH3+ (165), C5N3H7+ (F109) and C4N3H4+ (F82). In order to extract a time-constant of these dynamics we fitted the measurements by the formula: 2 𝑡 (𝑡 − 𝑡0 ) ) ) ⊗ [(𝑡 − 𝑡0 ) (𝐴𝑑𝑒𝑐𝑎𝑦 exp (− 𝑆𝐹𝑖𝑡 (𝑡) = 𝑒𝑥𝑝 (−4𝑙𝑛(2) ( ) + 𝐴𝑠𝑡𝑒𝑝 )] (2) 𝜏𝑐𝑟𝑜𝑠𝑠𝑐𝑜 𝜏𝑑𝑒𝑐𝑎𝑦

where the fitting parameters are ADecay, Astep, t0, τDecay and τcrossco. τcrossco is the cross-correlation between the two pulses at FWHM and τDecay is the decay duration. A step function (t – t0) is necessary to fit the long timescale signal (with an amplitude AStep). We extracted a time constant for all small fragments (CH3+ etc.) of τDecay,1 = 38 ± 3 fs, and for the large fragments 6


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(caffeine losing CH3, F109) of τDecay,2 = 28 ± 16 fs with identical cross-correlation duration (τcrossco) and zero delay (t0) parameters. These two dynamics are similar, within the error bar, indicating that the observed ultrafast relaxation is common to all fragments. The effects of the laser parameters (XUV photon energy spectrum and IR intensity) on the decay duration have also been investigated. For these studies, we constructed the normalized signal defined as:

Δ𝑆Norm (t) =

Δ𝑆(𝑡) , 𝑆XUV only + 𝑆IR only

(3)

which is the two-color signal rate. For the sake of clarity, in Fig. 3, we only show CH3+ measurements and its corresponding fitting curve. Very similar results are obtained with the other fragments. The first study concerns the XUV-photon energy dependency (Fig.3.a-b). We changed the gas from xenon to krypton in the HHG, shifting the photon energy center from 25 eV to 31 eV thus allowing to ionize deeper electronic states and also to increase the excess internal energy of the caffeine molecule. In Fig. 3.a-b, we see that the excitation of caffeine with XUV pulses generated in Kr results in a decrease of the two-color signal rate compared to HHG in Xe, the extracted decay lifetimes remain similar within the error bar (see also S.I. Figure S4). This demonstrates that in both cases the observed ultrafast dynamics has the same origin and it is more efficient when using lower energy photons. The second study concerns the IR intensity dependency. From Fig. 3.b-c we can clearly see that by increasing the IR intensity the two-color effect is enhanced, while the extracted decay lifetime remains unchanged. In other words, the IR intensity only affects the signal to noise ratio but it does not change the relaxation timescale. Therefore, while the fragmentation patterns and signal intensity depend on the laser parameters, the extracted timescales are very robust and weakly affected by the increase of 7



XUV-photon energy and IR intensity. The global scenario shows a transient state of the XUVexcited molecule where small fragments are more easily created by the IR probe, and which corresponds to excited cations that would otherwise dissociate to large fragments. These aspects have been investigated by using many-body quantum theory as described below. To further theoretically investigate the ultrafast relaxation dynamics of the highly-excited caffeine cation, we first calculated the vertical ionization energies and pole strengths of 996 doublet monocationic (Dn) states up to binding energy EB = 26 eV mimicking the states produced by the XUV ionization of the neutral caffeine. The geometry of the neutral singlet ground state was optimized at the B3LYP21/Def2-TZVP22 level of density functional theory. For the monocationic states, we used Symmetry Adapted Cluster/Configuration Interaction (SAC-CI) theory23,24,25 with shake-up corrections26 and the Def2-TZVP basis set without fpolarization functions combined with Dunning-Hay Rydberg (3s, 3p) basis set 27 (hereafter Def2-TZVP (−f) + Rydberg (3s, 3p) basis set) to describe highly-correlated shake-up excitations to Rydberg (3s, 3p) orbitals. The vertical ionization energies from the neutral ground states to the fifteen-low-lying singlet dicationic states were also calculated at the SACCI/Def2-TZVP level of theory. Because SAC-CI theory systematically under-estimates the ionization energy of CAFF28, the calculated energy levels were shifted such that the lowest electronic state for each charge was adjusted to the calculated value at the UBD(T)29 / Def2TZVP//B3LYP/Def2-TZVP level of coupled-cluster theory. The linewidth of each peak was determined by least-square fitting of pseudo-Voigt functions 30 , 31 to the experimental photoelectron spectrum measured by Feyer et al.32 Note that the FWHMs of the Lorentzians {γLi} of each line was optimized independently (see SI for the detailed computational procedure).

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Such computed photoelectron spectrum of caffeine close to the ionization threshold of the dicationic states at the SAC-CI/ Def2-TZVP (−f) + Rydberg (3s, 3p) level of theory is displayed in Figure 4a. together with the major part of the carbon 2s region. The vertical ionization energies to the dicationic states is also presented. The theoretical spectrum reproduces well the experimental24 peak position at EB = 23 eV and broad asymmetrical line shape in the region EB = 21-24 eV. This band consists of hundreds of shake-up states with 3pz (perpendicular to the molecular plane) Rydberg configurations as described in Table S1 in SI. These shake-up states are embedded in the dication manifold of EB ≥ 21.64 eV and are easily further ionized to dicationic states by the absorption of IR probe photon. We conclude that the XUV pump pulse ionizes the caffeine molecule to the 3pz Rydberg shake-up states with EB ≈ 21-25 eV. Consecutively, the system starts to relax through a large number of CIs between more than 100 states, with a passage time (effective lifetime) {τi} shorter than 1 fs, as shown in Fig. 4b. The time constants of {τi} < 1 fs are much shorter than the lifetime of the π1(π*)2 Feshbach resonance in adenine (~4 fs)

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which have the same

purine backbone (C5H4N4) as caffeine. Furthermore, the mean energy gap between the energetically nearest neighbor shake-up states within 21-26 V is typically less than 10 meV. This indicates that the XUV pulse excite the CAFF into strongly coupled CAFF+ states and CAFF+ rapidly undergoes IC cascades. We can thus assume that the autoionization to dicationic states is negligible11 and the time constant of ~40 fs found in the experiment corresponds nearly exclusively to the timescale of the IC cascade. We can therefore extract the time constant τNRD of this non-radiative decay cascade from the experimental spectrum using the linewidths of the individual shake-up states {τi}. These time constants can be obtained from the FWHMs of the Lorentzians {γLi} in the pseudo-Voigt functions used to reconstruct the photoelectron spectrum: 9


(4)


𝜏𝑖 =

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ℏ . 𝛾𝑖𝐿

The effective time constant of the IC cascade from each shake-up state can be evaluated by the cumulative lifetimes of the shake-up states such as: (5)

𝑛

𝜏𝑖cum =

∑

𝜏𝑖 .

{𝑖| 21.17 ≤ 𝐸𝐵 }

The ionization by the XUV pulse is one-photon process and it can simultaneously ionize CAFF molecule to all the shake-up states described in Figure 4a. The ionization cross section of the Di state is proportional to the pole-strength Pi 34:

(6) 2

𝑖 𝜎𝑖 ∝ 𝑃𝑖 = |⟨Ψ𝑞=0 |Ψ𝑞=1 ⟩| ,

where Ψ𝑞=0 is the electronic wave function of the electronic ground state of the neutral 𝑖 molecule and Ψ𝑞=1 is that of the i-th electronic excited state of the monocationic molecule.

Thus, the effective lifetime of the IC cascade when the XUV pulse ionizes up to the Dn state 𝜏𝑛eff can be written by the weighted average of 𝜏𝑖cum using 𝑃𝑖 : 𝜏𝑛eff

=

∑𝑛{𝑖| 21.17 ≤ 𝐸𝐵} 𝑃𝑖 𝜏𝑖cum ∑{𝑖| 21.17 ≤ 𝐸𝐵≤26} 𝑃𝑖

. (7)

The resultant 𝜏𝑖eff from 21.17 eV (which corresponds to the MO26-1 (D62) state with P62 = 0.42, see Table S1 in SI for more detailed electron configuration) to 25 eV (corresponding the central frequency of the Xe XUV pulse) is 44 ± 4 fs, as shown in Figure 5b, which is very close to the experimentally observed decay time constant of 40 fs. This indicates that the IC cascade can starts from the all shake-up states in 21-25 eV and their contribution is proportional to their pole strength. In other words, the experimental observed decay constant is the convolution of the IC cascades starting from all the shake-up states EB =21-25 eV with the weight proportional to {Pi}.

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Let us now analyze the probing mechanism. In the experiment, the decay time is observed through the measurement of the fragments. The fragmentation mechanism is initiated during the IC cascade as schematically shown in Figure 5. During the IC cascade, the IR probes the states with an energy higher than some critical value (E*) by further ionizing the caffeine monocation to the dissociative electronic excited states of the dication. This leads to the production of small fragments such as CH3+ and CO+ through a non-statistical process similar to a Coulomb explosion. Once the caffeine monocation relaxes into electronic states with energy lower than E*, the IR probe pulse cannot ionize the monocation to the dissociative dicationic states anymore but can further excite the monocation. The excited cation vibrationally heats up through an IVR process leading to statistical fragmentation from low-lying monocationic states producing larger fragments like C5H7N3+ (F109). Along this line, Feyer et al. also reported that the major photofragment obtained by the XUV irradiation of hνXUV = 21.21 and 16.67 eV is C5H7N3+, and neutral CO and CH3 are detected as minor products, while neither CO+ nor CH3+ were observed27. In addition, only few amounts of CH3+ and CO+ were observed in our experiment (Figure 1). These two evidences suggest that the XUV induced fragmentation of CAFF+ to large fragments mostly proceeded at the electronic state below 21 eV after further nonradiative decay process, and autoionization to the dicationic states is not significant. We have estimated the critical energy E* that determines the threshold for the observation of small fragments. This can be obtained by the difference between the height of the transition state ETS for the CH3+ dissociation in the lowest dicationic state and the central frequency of the IR probe pulse hνIR =1.55 eV E* = ETS − hνIR.

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(6)


The calculated value of ETS is 22.70 eV at the UB3LYP/Def2-TZVP level of density functional theory (see Figure S7) and thus the resultant value of E* is 21.14 eV, which is consistent with the energy EB(D62) = 21.17 eV, calculated at the SAC-CI level of theory, and with the lowest in energy state considered in the cascade. In summary, we investigated femtosecond dynamics of XUV excited caffeine cations using time-dependent mass spectrometry. We have shown that the process is driven by nonadiabatic cascade and a subsequent photofragmentation of the highly-excited caffeine molecules. The decay mechanism is explored with the aid of quantum chemistry calculations. We found that the XUV-excited caffeine molecule undergoes a relaxation cascade through more than 100 monocationic shake-up states with a time constant of about 40 fs. This dynamics drastically changes the photofragmentation process after the IR probe radiation. Before the cascade completes, caffeine monocation can be further ionized by the IR probe pulse and small fragments like CH3+ and CO+ are non-statistically generated via the dissociative electronic excited states of the dication. After the IC cascade, the IR probe cannot ionize anymore the monocation and larger fragments become dominant via statistical fragmentation pathways in low-lying monocationic states. These results show that the complex highly correlated electronic structure and nonadiabatic couplings are key ingredients to understand ultrafast reaction dynamics in highly excited molecules. Similar processes have also recently been observed in PAH molecules12 and named “correlation induced nonadiabatic relaxation”. The present work shows that this is a general behavior, not specific to PAH molecules and should then impact all prebiotic building blocks produced in interstellar media.

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Fig. 1: Ion yield ratios of the measured time-of-flight for photo-ionization of caffeine molecules by XUV pulses resulting from HHG in Xe (blue) or Kr (red). Main fragments are m/z = 109, 82 and 67.

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Fig. 2: (a) 3D map of the two-color signal evolution for all detected fragments as a function of the pump-probe delay. (b) Large fragments (as F109) exhibit instantaneous depopulation and re-population dynamics, whereas (c) the small fragment dynamics are opposite. Decay durations are extracted from fitting curves (red).

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Fig. 3: (a) Dependency of the CH3+ two-color signal rate as a function of the HHG gas generator and for different IR intensities. Low photon energy enhances the process, but, as it is shown in (b), the extracted decay times remain similar (the decay mean values and error bars displayed in (b) have been calculated on a larger set of data shown in Fig. S4) . (c) Amplitude of the two-color signal rate (Δ𝑆Norm (𝑡)) as a function of the IR intensity where a linear trend (dashed line) is observed. Both (b) and (c) demonstrate that the studied dynamics is not modified by the IR probe.

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Fig 4. Simulated photoelectron spectrum of caffeine at the SAC-CI level of theory. (a) Comparison between experimental spectrum measured by Feyer et al.12 and the SAC-CI result; black line: experimental result, red bars: SAC-CI computed cationic states, red line: computed spectrum obtained by convolution of the SAC-CI states by pseudo-Voigt functions; blue bars: positions of the low-lying dicationic states (b) Lifetimes of shake-up states (black dots, left axis), estimated by the linewidths of the Lorentzians in the pseudo-Voigt functions, and its effective lifetime (red line, right axis) as a function of the electron binding energy. The error bars correspondint to the 5 % uncertainty in the linewidths of the Lorentzians. For more detailed discussion on the error in the linewidth, see the section 3 of the SI.

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Fig 5. Schematic description of the fragmentation dynamics induced by the XUV-pump–IRprobe experiment. (a) Before the IC cascade completes, caffeine monocation can be further ionized to the dissociative electronic excited states of the dication by the IR probe pulse and small fragments like CH3+ and CO+ are nonstatistically generated. (b) After the IC cascade, the IR probe cannot ionize the monocation anymore by a one-photon process and the larger fragments becomes dominant via statistical fragmentation pathways in low-lying monocationic states.

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Supporting Information Detailed experimental and theoretical methods, uncertainly estimation on the calculated lifetime, discussions on possible final electronic states of caffeine dication created by the IR probe pulse, and the XYZ coordinates of the optimized structures.

Acknowledgements The research has been supported by CNRS, ANR-16-CE300012 “CIRCE” programme Blanc, fédération de physique Marie-Ampère, Italian Ministry of Research (Project FIRB No. RBID08CRXK). K. Y. and S. M. acknowledge a grant from the Japan Science and Technology Agency (JST) with Core Research for Evolutional Science and Technology (CREST, grant number JPMJCR14L5) in the Area of “Establishment of Molecular Technology towards the Creation of New Functions” at Hokkaido University. K. Y. is grateful for the financial support from Building of Consortia for the Development of Human Resources in Science and Technology, MEXT. Part of the calculations in this paper was carried out by using the supercomputers at Academic Center for Computing and Media Studies, Kyoto University and Okazaki Research Facilities (Research Center for Computational Science). V.D. and A.I.K. acknowledge financial support by DFG through QUTIF Priority Programme.

ORCID A. M.: 0000-0002-1703-0041 K. Y.: 0000-0002-7716-6274

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V.L.: 0000-0002-5986-6664 B. S.: 0000-0002-7376-4154 F. L.: 0000-0001-9040-919X Researcher ID K. Y. : G-1913-2017 References

(1) Agostini, P.; DiMauro, L.F. The Physics of Attoseconde Light Pulses. Rep. Prog. Phys.

2004, 67, 813-855. (2) Krausz, F.; Ivanov, M. Attosecond Physics. Attosecond Physics. Rev. Mod. Phys. 2009, 81, 163-234. (3) Leone, S. R.; McCurdy, C. W.; Burgdorfer, J.; Cederbaum, L.; Chang, Z.; Dudovich, M.; Feist, J.; Greene, C.; Ivanov, Kienberger, R. et al., Attosecond Science - What Will It Take to Observe Processes in 'Real Time', Nat. Photon. 2014, 8, 162-166. (4) Nisoli, M.; Decleva, P.; Calegari, F.; Palacios, A; Martín, F. Attosecond Electron Dynamics in Molecules, Chem. Rev. 2017 117, 10760-10825. (5) Ullrich, S.; Schultz, T.; Zgierskia, M. Z.; Stolow, A. Electronic Relaxation Dynamics in DNA and RNA Bases Studied by Time-Resolved Photoelectron Spectroscopy. Phys. Chem. Chem. Phys. 2004, 6, 2796-2801. (6) Suzuki, T. Time-Resolved Photoelectron Spectroscopy of Non-Adiabatic Electronic Dynamics in Gas and Liquid Phases. Int. Rev. Phys. Chem. 2012, 31, 265-318. (7) Horio, T.; Spesyvtsev, R., Nagashima, K.; Ingle, R. A.; Suzuki, Y.; Suzuki, T., Full Observation of Ultrafast Cascaded Radiationless Transitions from S2 (ππ∗) State of Pyrazine Using Vacuum Ultraviolet Photoelectron Imaging, J. Chem. Phys. 2016, 145, 044307. (8) Horio, T.; Suzuki, Y.; Suzuki, T. Ultrafast Photodynamics of Pyrazine in the Vacuum Ultraviolet Region Studied by Time-Resolved Photoelectron Imaging using 7.8-eV Pulses, J. Chem. Phys. 2016, 145, 044307. (9) Ehara, M.; Ohtsuka, Y.; Nakatsuji, H.; Takahashi, M.; Udagawa, Y., Theoretical Fine Spectroscopy with Symmetry-Adapted-Cluster Configuration-Interaction Method: Outerand Inner-Valence Ionization Spectra of Furan, Pyrrole, and Thiophene, J. Chem. Phys. 2005, 122, 234319. 19



(10) Remacle, F.; Levine, R.D. An Electronic Time Scale for Chemistry, Proc. Natl. Acad. Sci. USA 2006, 103, 6793-6798. (11) Calegari, F.; Ayuso, D.; Trabattoni, A.; Belshaw, L.; De Camillis, S.; Anumula, S.; Frassetto, F.; Poletto, L.; Palacios, A.; Decleva, P. et al., Ultrafast Electron Dynamics in Phenylalanine Initiated by Attosecond Pulses, Science 2014, 346, 336-339. (12) Hennig, H.; Breidbach, J.; Cederbaum, L.S. Electron Correlation as the Driving Force for Charge Transfer: Charge Migration Following Ionization in N-Methyl Acetamide, J. Phys. Chem. A 2005, 109, 409–414. (13) Kuleff, A. I.; Cederbaum, L. S. Ultrafast Correlation-Driven Electron Dynamics, J. Phys. B: Atom. Mol. Opt. Phys., 2014, 47, 124002. (14) Boudaı̈ ffa, B.; Cloutier, P.; Hunting, D.; Huels, M. A.; Sanche, L. Resonant Formation of DNA Strand Breaks by Low-Energy (3 to 20 eV) Electrons, Science 2000, 267, 1658– 1660. (15) Tielens, A.G.G.M. Interstellar Polycyclic Aromatic Hydrocarbon Molecules, Ann. Rev. Astron. Astrophys. 2008, 46, 289-337. (16) Marciniak, A.; Despré, V.; Barillot, T.; Rouzée, A.; Galbraith, M.C.E.; Klei, J.; Yang, C.H.; Smeenk, C.T.L.; Loriot, V.; Nagaprasad Reddy, S. et al., XUV Excitation Followed by Ultrafast Non-Adiabatic Relaxation in PAH Molecules as a FemtoAstrochemistry Experiment. Nat. Comm. 2015, 6, 7909. (17) A. Marciniak et al. (submitted) (18) P. Callahan, M.; Smith, K. E.; Cleaves II, H. J.; Ruzicka, J.; Stern, J. C.; Glavin, D. P.; House, C. H.; Dworkin, J.P. Carbonaceous Meteorites Contain a Wide Range of Extraterrestrial Nucleobases. Proc. Natl. Acad. Sci. USA 2011, 108, 13995-13998. (19) Chen, J.; Kohler, B. Ultrafast Nonradiative Decay by Hypoxanthine and Several Methylxanthines in Aqueous and Acetonitrile Solution. Phys Chem. Chem. Phys. 2012, 14, 10677-10682. (20) Reduzzi, M. ; Hummert, J.; Dubrouil, A.; Calegari, F.; Nisoli, M.; Frassetto, F.; Poletto, L.; Chen, S.; Wu, M.; B. Gaarde,M. et al., Polarization Control of Absorption of Virtual Dressed States in Helium. Phys. Rev. A 2015, 92, 033408. (21) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648–5652.

(22) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297-3305. (23) Nakatsuji, N. Cluster Expansion of the Wavefunction. Excited States. Chem. Phys. Lett. 1978, 59, 362–364. 20


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(24) Nakatsuji, H. Cluster Expansion of the Wavefunction. Calculation of Electron Correlations in Ground and Excited States by SAC and SAC CI Theories. Chem. Phys. Lett. 1979, 67, 334–342. (25) Nakatsuji, H. Cluster Expansion of the Wavefunction. Electron Correlations in Ground and Excited States by SAC (Symmetry-Adapted-Cluster) and SAC CI Theories. Chem. Phys. Lett. 1979, 67, 329–333. (26) Honda, Y.; Hada, M.; Ehara, M.; Nakatsuji, H. Excited and Ionized States of Aniline: Symmetry Adapted Cluster Configuration Interaction Theoretical Study. J. Chem. Phys. 2002, 117, 2045–2052. (27) Duninng Jr., T. H.; Harrison, P. J. In Modern Theoretical Chemistry Vol. 2; Shaffer II, H. F., Ed.; Plenum Press, New York, the US; 1977. (28) Farrokhpour, H.; Fathi, F. Theoretical Study of Valance Photoelectron Spectra of Hypoxanthine, Xanthine, and Caffeine Using Direct Symmetry-Adapted Cluster/configuration Interaction Methodology. J. Comput. Chem. 2011, 32 , 2479–2491. (29) Handy, N. C.; Pople, J. A.; Head-Gordon, M.; Raghavachari, K.; Trucks, G. W. SizeConsistent Brueckner Theory Limited to Double Substitutions. Chem. Phys. Lett. 1989, 164, 185–192. (30) Thompson, P.; Cox, D. E.; Hastings, J. B. IUCr. Rietveld Refinement of Debye–Scherrer Synchrotron X-Ray Data from Al2O3. J. Appl. Crystallogr. 1987, 20, 79–83. (31) Ida, T.; Ando, M.; Toraya, H. IUCr. Extended Pseudo-Voigt Function for Approximating the Voigt Profile. J. Appl. Crystallogr. 2000, 33, 1311–1316. (32) Feyer, V.; Plekan, O.; Richter, R.; Coreno, M.; Prince, K. C. Photoion Mass Spectroscopy and Valence Photoionization of Hypoxanthine, Xanthine and Caffeine. Chem. Phys. 2009, 358, 33–38. (33) Fennimore, M. A. ; Matsika, S. Electronic Resonances of Nucleobases Using Stabilization Methods. J. Phys. Chem. A 2018, 122, 4048-4057 (34) von Niessen, W.; Schirmer, J.; Cederbaum, L.S. Computational Methods for the OneParticle Green's Function. Comput. Phys. Rep. 1984, 1, 54-125.

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Ultrafast Nonadiabatic Cascade and Subsequent Photofragmentation

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