In this perspective, we review experiments with molecules picked up on large clusters in molecular beams with the focus on the processes in atmospheric and interstellar chemistry. First, we concentrate on the pickup itself, and we discuss the pickup cross sections. We measure the uptake of different atmospheric molecules on mixed nitric acid–water clusters and determine the accommodation coefficients relevant for aerosol formation in the Earth's atmosphere. Then the coagulation of the adsorbed molecules on the clusters is investigated. In the second part of this perspective, we review examples of different processes triggered by UV-photons or electrons in the clusters with embedded molecules. We start with the photodissociation of hydrogen halides and Freon CF₂Cl₂ on ice nanoparticles in connection with the polar stratospheric ozone depletion. Next, we mention reactions following the excitation and ionization of the molecules adsorbed on clusters. The first ionization-triggered reaction observed between two different molecules picked up on the cluster was the proton transfer between methanol and formic acid deposited on large argon clusters. Finally, negative ion reactions after slow electron attachment are illustrated by two examples: mixed nitric acid–water clusters, and hydrogen peroxide deposited on large Ar_N and (H₂O)_N clusters. The selected examples are discussed from the perspective of the atmospheric and interstellar chemistry, and several future directions are proposed.

The formation of negative ions following electron impact to ethanol (CH₃CH₂OH) and trifluoroethanol (CF₃CH₂OH) is studied in the gas phase by means of a crossed electron–molecular beam experiment and in the condensed phase via Electron Stimulated Desorption (ESD) of fragment ions from the corresponding molecular films under UHV conditions. Gas phase ethanol exhibits two pronounced resonances, located at 5.5 eV and 8.2 eV, associated with a remarkable selectivity in the decomposition of the precursor ion. While the low energy resonance exclusively decomposes into O⁻, that at higher energy generates OH⁻ and a comparatively small signal of [CH₃CH₂O]⁻ due to the loss of a neutral hydrogen. CF₃CH₂OH shows a completely different behaviour, as now an intense feature at 1.7 eV appears associated with the loss of a neutral hydrogen atom exclusively occurring at the O site. The H⁻ formation from the gas phase compounds is below the detection limit of the present experiment, while in ESD from 3 MonoLayer (ML) films of CH₃CH₂OH and CF₃CH₂OH the most intense fragment is H⁻, appearing from a broad resonant feature between 7 and 12 eV. With CF₃CH₂OH, by using the isotopically-labelled analogues CF₃CD₂OH and CF₃CH₂OD it can be shown that this feature consists of two resonances, one located at 8 eV leading to H⁻/D⁻ loss from the O site and a second resonance located at 10 eV leading to the loss of H⁻/D⁻ from the CH₂ site.

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.

Pure acetylene and mixed Ar-acetylene clusters are formed in supersonic expansions of acetylene/argon mixtures and analysed using reflectron time-of-flight mass spectrometer with variable electron energy ionization source. Acetylene clusters composed of more than a hundred acetylene molecules are generated at the acetylene concentration of ≈8%, while mixed species are produced at low concentrations (≈0.7%). The electron energy dependence of the mass spectra revealed the ionization process mechanisms in clusters. The ionization above the threshold for acetylene molecule of 11.5 eV results in the main ionic fragment progression ${\left({\mathrm{C}}_2{\mathrm{H}}_2\right)}_n^{+}$ . At the electron energies ⩾21.5 eV above the CH+CH⁺ dissociative ionization limit of acetylene the fragment ions nominally labelled as (C₂H₂)_nCH⁺, n ⩾ 2, are observed. For n ⩽ 7 these fragments correspond to covalently bound ionic structures as suggested by the observed strong dehydrogenation [(C₂H₂)_n − k × H]⁺ and [(C₂H₂)_nCH − k × H]⁺. The dehydrogenation is significantly reduced in the mixed clusters where evaporation of Ar instead of hydrogen can stabilize the nascent molecular ion. The ${\mathrm{C}}_3{\mathrm{H}}_3^{+}$ ion was previously assigned to originate from the benzene molecular ion; however, the low appearance energy of ≈13.7 eV indicates that a less rigid covalently bound structure of ${\mathrm{C}}_6{\mathrm{H}}_6^{+}$ ion must also be formed upon the acetylene cluster electron ionization. The appearance energy of Ar_n(C₂H₂)⁺ fragments above ≈15.1 eV indicates that the argon ionization is the first step in the fragment ion production, and the appearance energy of ${\mathrm{Ar}}_{n\ge 2}{\left({\mathrm{C}}_2{\mathrm{H}}_2\right)}_{m\ge 2}^{+}$ at ≈13.7 eV is discussed in terms of an exciton transfer mechanism.