The 2023 Nobel Prize in Physics recognized attosecond science and technology, which allows us to understand and control the properties of matter by accessing electron dy-namics at the Angstrom length scale. Attosecond science and technology are currently being applied to investigate all phases of matter and have garnered particular attention in the field of light-induced processes in molecules. After two decades of development, an attosecond perspective on molecular processes has become a tangible reality thanks to advanced experiments and theories. However, so far, this has only been applied to small model systems. This article discusses the current state of the field and explores how it could expand to include the study of complex structures, including large biomolecules.

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

Doubly charged molecular cations often carry signatures of electronic correlation and electron-nuclear entanglement present in the parent cation. Here, we produce ethylene dications using a combination of an extreme ultraviolet pump and near-infrared probe pulses, observing a peak in the dication yield at a pump-probe delay of approximately 15 fs. Ab-initio calculations, which explicitly take into account coupled electron-nuclear dynamics induced by the pump and the multiphoton nature of the probe-induced ionization step, reproduced the observed delay in the yield. It originates from resonant enhancement of the multiphoton ionization of the electronically excited ethylene cation as the carbon-carbon double bond expands. However, this effect is tempered by rapid nonadiabatic relaxation of the excited ionic states. Our results suggest a general mechanism whereby ultrafast nonadiabatic relaxation of a molecular ion can compete with its strong-field ionization rate, confining the dication yield to a narrow temporal window of a few femtoseconds.

Attosecond technologies based on high harmonic generation (HHG) allow us to probe the fundamental properties of light–matter interactions with an unprecedented level of temporal and spatial resolution. HHG-based light sources deliver attosecond pulses of extreme ultraviolet photons that can easily ionize isolated molecules in the gas phase. This ultrafast ionization results in various physical phenomena involving pure electronic or coupled electronic and nuclear mechanisms. These mechanisms lead to charge and energy dynamics at the angstrom length scale that impact the fate of the system on longer timescales. Significant progress has been made in studying small polyatomic molecules with attosecond pulses. These advances raise the question of whether the physical processes observed in small isolated molecules can also be studied as the size of the systems approaches the nanometric domain and eventually reaches the domain of molecular nanomaterials. In this article, we discuss examples of phenomena exhibiting scale invariances that can be used to predict the outcomes of interactions between light pulses and increasingly complex systems. Specifically, we discuss electron scattering on the attosecond timescale and electron–phonon dynamics in photoionized species, highlighting universal mechanisms that manifest in these building blocks of molecular nanomaterials. This work also raises new questions for future experiments in complex molecular materials.

Attosecond chemistry involves developing strategies to manipulate electronic coherent waves in molecules, which can influence the outcome of photoinduced reactions. While recent progress in this field calls for investigations of increasingly complex isolated or embedded systems, theoretical predictions on attosecond charge migration have remained limited to native neutral species. Since molecules in nature often carry a native charge, there is potential biological and chemical interest in determining whether attosecond charge migration is affected by an additional charge. In this study, we employ high-level correlated methods to study purely electronic dynamics induced by hole-mixing in molecular ions. Our results, obtained for a series of neutral, protonated and deprotonated molecules, reveal that the likelihood of observing attosecond electron dynamics can either be degraded or improved by the presence of an initial charge, and that the existence of the dynamics is correlated with the strength of electron correlation. These findings will stimulate further experimental and theoretical investigations into this unexplored field of attosecond dynamics in molecular ions.

Symmetry governs nature’s laws, yet many of the natural phenomena occur due to the breakdown of symmetry. Here, we show how isotope-induced inversion symmetry breaking influences ultrafast photoisomerization processes in ethylene. Using extreme ultraviolet pump – near infrared probe time-of-flight mass spectrometry, we find that replacing one of the carbon atoms in ethylene with a 13C isotope leads to twice-faster structural relaxation via ethylene-ethylidene isomerization in the photo-excited molecular cation. Advanced trajectory surface hopping calculations incorporating the nuclear symmetry of the molecular systems, reveal that it arises from the mixing of different normal modes in the isotope-substituted species, interactions otherwise forbidden by symmetry. Although the mixing does not alter the symmetry of the electronic Hamiltonian, it modifies that of the nuclear Hamiltonian, causing explicit symmetry breaking. This facilitates efficient intra-molecular vibrational energy redistribution, lowering the isomerization yield. Our findings offer opportunities to use isotope-induced nuclear symmetry breaking to control the outcome of light-molecule interactions across ultrafast timescales. Symmetry breaking plays a crucial role in natural phenomena, yet its mechanisms remain poorly understood in photochemistry. Here, the authors demonstrate that isotope-induced inversion symmetry breaking accelerates ultrafast relaxation in ethylene via photoisomerization, revealing potential for controlling light-molecule interactions through nuclear symmetry manipulation.

Attosecond ionization time-delays at photoelectron energies above typically 10 eV are usually interpreted using the so called asymptotic approximation as a sum of the atomic or molecular delays with a universal laser-induced contribution. Here, we employ a two-harmonic RABITT (Reconstruction of Attosecond Beating by Interference of Two-photon Transitions) configuration to isolate the multiphoton pathways and measure the ionization time delays as a function of the dressing field intensity. We show that the validity of the asymptotic theory can be extended to the threshold or to higher-order contributions by rigorously treating the angular-momentum dependence of the continuum-continuum transitions into universal and easily computable partial-wave-specific correction factors. Our asymptotic treatment is also valid for higher-order interfering amplitudes while significantly simplifying their evaluation and providing a transparent physical interpretation. The validity of the method for atomic and molecular targets in the vicinity of resonances, ionization thresholds, and for both the emission-integrated and angularly resolved signal is confirmed by comparison to ab initio calculations over a wide energy range.

Photoionization of acetylene by extreme ultraviolet light results in a stand-alone contribution from the outermost valence orbital, followed by well-separated photoelectron bands from deeper molecular orbitals. This makes acetylene an ideal candidate for probing the photoionization dynamics in polyatomic molecules free from the spectral congestion often arising after interaction with an attosecond pulse train. Here, using an angle-resolved attosecond interferometric technique, we extract the photoionization time delays for the outermost valence orbital in acetylene relative to an atomic target, namely argon. Compared to argon, the photoemission from the acetylene molecule is found to be advanced by almost 28 attoseconds. The strong variation of the relative photoionization time delays as a function of the photoemission angle was interpreted using an analytical model based on semiclassical approximations to be the interplay between different short-range potentials along and perpendicular to the molecular axis. Our results highlight the importance of using attosecond time-resolved measurements to probe the nonspherical nature of the molecular potential, even in the case of relatively small, linear systems.

This roadmap reviews the new, highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The Review highlights several recent advances in the field and provides a roadmap for the development of the field over the next decade. Condensed matter systems exposed to radiation can be inorganic, organic, or biological, finite or infinite, composed of different molecular species or materials, exist in different phases, and operate under different thermodynamic conditions. Many of the key phenomena related to the behavior of irradiated systems are very similar and can be understood based on the same fundamental theoretical principles and computational approaches. The multiscale nature of such phenomena requires the quantitative description of the radiation-induced effects occurring at different spatial and temporal scales, ranging from the atomic to the macroscopic, and the interlinks between such descriptions. The multiscale nature of the effects and the similarity of their manifestation in systems of different origins necessarily bring together different disciplines, such as physics, chemistry, biology, materials science, nanoscience, and biomedical research, demonstrating the numerous interlinks and commonalities between them. This research field is highly relevant to many novel and emerging technologies and medical applications.

There is renewed interest in the structure of the essential amino acid phenylalanine in the solid state. Three new polymorphs were found in the years 2012 to 2014. Here, we investigate the structure, stability, and energetical ordering of these phases using first-principles simulations at the level of density functional theory incorporating van der Waals interactions. Two of the distinct crystal forms are found to be structurally similar and energetically very close after vibrational free energy corrections have been taken into account. Infrared absorption spectra are likewise calculated and compared to experimental measurements. By combining measurements obtained with a commercial Fourier transform infra-red spectrometer and a homemade air-photonics-based THz time domain spectrometer, we could carry out this comparison in the vibrational frequency region from 1 to 40 THz. The excellent agreement of the line positions and the established energy ranking allow us to identify the most stable polymorph of phenylalanine.

High photon energy excitation is of prior importance for photophysics and photochemistry in space. In that context, laboratory experiments using ionizing radiations delivered by synchrotron have provided information on the final product of the interaction. New generation of light sources provides the combination of high energy photons and short pulse duration that allows studying charge, energy and structural changes in real time. Here we report recent experiments based on high harmonic generation sources, performed on polycyclic aromatic hydrocarbons and diamondoids. These results describe the energy dynamics in electronic and nuclear degrees of freedom, showing the role of electron correlation, non-adiabatic processes and quantum coherence. It opens the way to new investigations that can quantify all reaction pathways in extreme ultraviolet excited species of astrochemical interest.

Carbohydrate sequencing is a formidable task identified as a strategic goal in modern biochemistry. It relies on identifying a large number of isomers and their connectivity with high accuracy. Recently, gas phase vibrational laser spectroscopy combined with mass spectrometry tools have been proposed as a very promising sequencing approach. However, its use as a generic analytical tool relies on the development of recognition techniques that can analyse complex vibrational fingerprints for a large number of monomers. In this study, we used a Bayesian deep neural network model to automatically identify and classify vibrational fingerprints of several monosaccharides. We report high performances of the obtained trained algorithm (GlAIcomics), that can be used to discriminate contamination and identify a molecule with a high degree of confidence. It opens the possibility to use artificial intelligence in combination with spectroscopy-augmented mass spectrometry for carbohydrates sequencing and glycomics applications.

We present a new experimental set-up combining ultrafast XUV technics with electrospray sources. First results of ultrafast dynamics in large molecular ions are shown demonstrating perspectives for applications in attochemistry.

Specific fragmentation patterns are fingerprints that allow for unambiguous identification of molecules, for instance in analytical methods. To reveal and possibly control such specific fragmentation, it is essential to understand the physical processes involved during the activation step. We have performed "on-the-fly" (without trapping device) femtosecond (fs) laser activation/mass spectrometry experiments on gas phase protonated reserpine, a model molecular ion for analytical purpose, at different wavelengths and laser pulse intensities. In contrast to collision induced dissociation (CID) or 267 nm fs-laser activation, evidence of non-statistical fragmentation is observed when using 800 nm fs-laser activation. The associated mechanisms are discussed in terms of fragmentation induced by Coulomb repulsion after ultrafast ionization of the protonated molecule. Our results illustrate that the present "on-the-fly" experimental scheme can help in the understanding of the physics behind fs-laser activation. (c) 2021 Elsevier B.V. All rights reserved.

Following ionization by an extreme ultraviolet (XUV) attosecond pulse train, a polyatomic molecule can be promoted to more-than-one excited states of the residual ion. The ensuing relaxation dynamics is often facilitated by several reaction coordinates, making them difficult to disentangle by the usual spectroscopic means. Here, we show that in atto-chemistry isotope labeling can be an efficient tool for unraveling the relaxation pathways in highly excited photoionized molecules. Employing an XUV pump pulse and a near-infrared probe pulse, we found the nuclear as well as coupled electron-nuclear dynamics in ethylene to be almost 40% faster compared to that of its deuterated counterpart. The findings, which are supported by advanced nonadiabatic dynamics calculations, led to the identification of the relevant nuclear coordinates controlling the relaxation. Our experiment highlights the relevance of ultrashort XUV pulses to capture the isotopic effect in few-femtosecond molecular photodynamics.

Imaging in real time the complete dynamics of a process as fundamental as photoemission has long been out of reach because of the difficulty of combining attosecond temporal resolution with fine spectral and angular resolutions. Here, we achieve full decoding of the intricate angle-dependent dynamics of a photoemission process in helium, spectrally and anisotropically structured by two-photon transitions through intermediate bound states. Using spectrally and angularly resolved attosecond electron interferometry, we characterize the complex-valued transition probability amplitude toward the photoelectron quantum state. This allows reconstructing in space, time, and energy the complete formation of the photoionized wave packet.

We present experiments where extreme ultraviolet femtosecond light pulses are used to photoexcite large molecular ions at high internal energy. This is done by combining an electrospray ionization source and a mass spectrometer with a pulsed light source based on high harmonic generation. This allows one to study the interaction between high energy photons and mass selected ions in conditions that are accessible on large-scale facilities. We show that even without an ion trapping device, systems as large as a protein can be studied. We observe light induced dissociative ionization and proton migration in model systems such as reserpine, insulin and cytochrome c. These results offer new perspectives to perform time-resolved experiments with ultrashort pulses at the heart of the emerging field of attosecond chemistry.

Gas phase experiments combined with ultrafast technologies can provide information on the intrinsic properties of molecular systems at picosecond, femtosecond, or even attosecond timescales. However, these experiments are often limited to relatively simple model systems. In this context, electrospray ionization sources (ESI) have offered new perspectives as they allow to produce large or fragile molecular ions in the gas phase, mimicking molecules in their natural environment. While time-resolved UV-visible ultrafast experiments on molecular ions have been successfully developed over the past decades, efforts are still required to perform experiments using ultrashort extreme ultraviolet (XUV) pulses with the goal of reaching attosecond resolution. In this article, we present recent results obtained using the combination of ultrafast technologies and ESI sources. We show that ultrafast dynamics experiments can be performed on molecular ions without ion trapping devices and can reveal UV-induced charge transfer in small peptides with controlled micro-environment. Non-adiabatic relaxation dynamics in large (bio)molecular ions is also presented. Such experiments are compatible with high harmonic generation XUV sources as shown here in the case of a metal complex. These ultrafast dynamics studies on large molecular ions offer new perspectives in attosecond science.

Two-color air plasma-based broadband terahertz (THz) generation and subsequent air-biased coherent detection (ABCD) of the THz field are presented. Both source and detection systems are characterized experimentally and numerically, yielding excellent agreement of measured and simulated signals. We reveal that it is crucial to model the whole optical setup and include the various pump distortions, like temporal and spatial walk-off as well as ellipticity of polarization, in order to interpret the experimental measurements correctly. Moreover, it turns out that geometrical effects in the ABCD scheme shape the recorded THz spectra and need to be taken into account. We confirm that THz electric fields with peak amplitude in the MV/cm range and large spectral bandwidth are produced, allowing us to demonstrate THz spectroscopy with molecular samples.