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The photodetachment and stability of R-Mandelate, the deprotonated form of the R-Mandelic acid, was investigated by observing the neutral species issued from either simple photodetachment or dissociative photodetachment in a cold anions set-up. R-Mandalate has the possibility to form an intramolecular ionic hydrogen-bond between adjacent hydroxyl and carboxylate groups. The potential energy surface along the proton transfer (PT) coordinate between both groups (O

Excited State Hydrogen Transfer (ESHT), proposed at the end of the 20th century by the corresponding authors, has been observed in many neutral or protonated molecules and become a new paradigm to understand excited state dynamics/photochemistry of aromatic molecules. For example, a significant number of photoinduced proton-transfer reactions from X–H bonds have been re-defined as ESHT, including those of phenol, indole, tryptophan, aromatic amino acid cations and so on. Photo-protection mechanisms of biomolecules, such as isolated nucleic acids of DNA, are also discussed in terms of ESHT. Therefore, a systematic and up-to-date description of ESHT mechanism is important for researchers in chemistry, biology and related fields. In this review, we will present a general model of ESHT which unifies the excited state proton transfer (ESPT) and the ESHT mechanisms and reveals the hidden role of ESPT in controlling the reaction rate of ESHT. For this purpose, we give an overview of experimental and theoretical work on the excited state dynamics of phenol–(NH3)n clusters and related molecular systems. The dynamics has a significant dependence on the number of solvent molecules in the molecular cluster. Three-color picosecond time-resolved IR/near IR spectroscopy has revealed that ESHT becomes an electron transfer followed by a proton transfer in highly solvated clusters. The systematic change from ESHT to decoupled electron/proton transfer according to the number of solvent molecules is rationalized by a general model of ESHT including the role of ESPT.

Time-evolutions of excited state hydrogen transfer (ESHT) in phenol (PhOH)-(NH3)2 clusters have been measured by three-color picosecond (ps) ultraviolet (UV)-near infrared (NIR)-UV pump-probe ion dip spectroscopy. The formation of a reaction product, ˙NH4NH3, is detected by its NIR absorption due to a 3p-3s Rydberg transition. The ESHT reactions from all of the vibronic levels show biexponential time-evolutions, even from the S1 origin. Based on the biexponential time-evolution, it is suggested that there is a second reaction path via the triplet πσ* state, which gives the slow component. The fast time-evolution of the ESHT reaction from the S1 origin is measured to be 268 ps, which is 10-times slower than that in PhOH-(NH3)3, and a higher barrier between the ππ* and reactive πσ* states is suggested. The size dependence of the ESHT reaction rates is discussed based on a potential distortion due to the proton transferred state in the ππ* potential surface.

Recent experimental work revealed that the lifetime of the S3 state of protonated 7-azaindole is about ten times slower than that of protonated 6-azaindole. We simulated the nonradiative decay pathways of these molecules using trajectory surface hopping dynamics after photoexcitation into S3 to elucidate the reason for this difference. Both isomers mainly follow a common pp* relaxation pathway involving multiple state crossings while coming down from S3 to S1 in the subpicosecond time scale. However, the simulations reveal that the excited-state topographies are such that while the 6-isomer can easily access the region of nonadiabatic transitions, the internal conversion of the 7-isomer is delayed by a pre-Dewar bond formation with a boat conformation.

International audience; Recent experimental work revealed that the lifetime of the S3 state of protonated 7-azaindole is about ten times longer than that of protonated 6-azaindole. We simulated the nonradiative decay pathways of these molecules using trajectory surface hopping dynamics after photoexcitation into S3 to elucidate the reason for this difference. Both isomers mainly follow a common ππ* relaxation pathway involving multiple state crossings while coming down from S3 to S1 in the subpicosecond time scale. However, the simulations reveal that the excited-state topographies are such that while the 6-isomer can easily access the region of nonadiabatic transitions, the internal conversion of the 7-isomer is delayed by a pre-Dewar bond formation with a boat conformation.

The decarboxylation (CO

International audience; A detailed understanding of radiative and nonradiative processes in peptides containing an aromatic chromophore requires the knowledge of the nature and energy level of low-lying excited states that could be coupled to the bright 1 * excited state. Isolated aromatic amino acids and short peptides provide benchmark cases to study, at the molecular level, the photoinduced processes that govern their excited state dynamics. Recent advances in gas phase laser spectroscopy of conformer-selected peptides have paved the way to a better, yet not fully complete, understanding of the influence of intramolecular interactions on the properties of aromatic chromophores. This review aims at providing an overview of the photophysics and photochemistry at play in neutral and charged aromatic chromophore containing peptides, with a particular emphasis on the charge (electron, proton) and energy transfer processes. A significant impact is exerted by the experimental progress in energy-and time-resolved spectroscopy of protonated species, which leads to a growing demand for theoretical supports to accurately describe their excited state properties.

International audience; The problem for molecular identification knows many solutions which include mass spectrometers whose mass sensitivity depends on the performance of the detector involved. The purpose of this article is to show by means of molecular dynamics simulations, how a laser-cooled ion cloud, confined in a linear radio-frequency trap, can reach the ultimate sensitivity providing the detection of individual charged heavy molecular ions. In our simulations, we model the laser-cooled Ca + ions as two-level atoms, confined thanks to a set of constant and time oscillating electrical fields. A singly-charged molecular ion with a mass of 10 6 amu is propelled through the ion cloud. The induced change in the fluorescence rate of the lather is used as the detection signal. We show that this signal is due to a significant temperature variation triggered by the Coulombian repulsion and amplified by the radio-frequency heating induced by the trap itself. We identify the optimum initial energy for the molecular ion to be detected and furthermore, we characterize the performance of the detector for a large range of confinement voltages.

International audience; The photodetachment energy threshold, as well as vibrationally-resolved spectral signatures of the lower lying excited states and dipole bound states in model aromatic phosphonate, sulfonate and phosphate oxyanions have been investigated using a photofragmentation spectrometer equipped with a cold ion trap. The effect of the laser excitation was monitored by mass-selective detection of product ion fragments or, alternatively, measuring the yield of the complementary neutral radicals discriminated according to their kinetic energy. The anions phenylphosphate, phenylsulfonate and p-toluenesulfonate evidenced the expected behaviour, characterised by the predominance of ionic fragmentation processes, at low energies, rapidly evolving to a scenario controlled by the electron photodetachment channel at higher energies. Surprisingly for such a similar system, the phenylphosphonate anion does not have any ionic fragmentation channels and only exhibits the presence of dipole bound states.

The European physical journal / D 75(5), 152 (2021). doi:10.1140/epjd/s10053-021-00155-y, This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science., Published by Springer, Heidelberg

International audience; Electron photodetachment of cold deprotonated indole and azaindole anions has been studied by use of a mass-selective photofragmentation spectrometer capable of negative ion and neutral particle detection. The electron affinities of the indolyl radical and the 5-, 6-and 7-azaindolyl radicals have been measured with an uncertainty of less than 0.002 eV. The presence of the nitrogen atom in the six-membered ring of the azaindolide anions stabilises the electron by 0.3 to 0.4 eV, i.e. about 10-15 %, compared to the indolide anion. No fragmentation was observed in either the anionic or radical forms of the species studied. The appearance of dipole-bound states in the spectra of deprotonated 6-and 7-azaindole anions allowed us to analyse the vibrational structure of the neutral 6-and 7azaindolyl radicals produced following photodetachment. Although no dipole-bound states were clearly identified for deprotonated indole or 5-azaindole, the shape of the photodetachment threshold suggests the presence of a very weakly dipole-bound state or dipole resonance, which cannot be resolved with our laser resolution.

International audience; We present a study of the photofragmentation of three protonated azaindole molecules-7azaindole, 6-azaindole, and 5-azaindole-consisting of fused pyrrole-pyridine bicyclic aromatic systems, in which the pyridinic (protonated) nitrogen heteroatom is located at the 7, 6, and 5 positions, respectively. Photofragmentation electronic spectra of the isolated aforementioned azaindolinium cations reveal that their photodynamics extends over timescales covering nine orders of magnitude and provide evidence about the resultant fragmentation pathways. Moreover, we show how the position of the heteroatom in the aromatic skeleton influences the excited state energetics, fragmentation pathways, and fragmentation timescales. Computed ab initio adiabatic transition energies are used to assist the assignation of the spectra, while geometry optimisation in the excited electronic states as well as ab initio calculations along the potential surfaces demonstrate the role of ππ/πσ* coupling and/or large geometry changes in the dynamics of these species. Evidence supporting the formation of Dewar valence isomers as intermediates involved in subpicosecond relaxation processes is discussed.

International audience; The photocatalytic oxidation of water with molecular or polymeric N-heterocyclic chromophores is a topic of high current interest in the context of artificial photosynthesis, that is, the conversion of solar energy to clean fuels. Hydrogen-bonded clusters of N-heterocycles with water molecules in a molecular beam are simple model systems for which the basic mechanisms of photochemical water oxidation can be studied under well-defined conditions. In this work, we explored the photoinduced H-atom transfer reaction in pyrimidine-water clusters yielding pyrimidinyl and hydroxyl radicals with laser spectroscopy, mass spectrometry and trajectory-based ab initio molecular dynamics simulations. The oxidation of water by photoexcited pyrimidine is unequivocally confirmed by the detection of the pyrimidinyl radical. The dynamics simulations provide information on the time scales and branching ratios of the reaction. While relaxation to local minima of the S1 potential-energy surface is the dominant reaction channel, the H-atom transfer reaction occurs on ultrafast time scales (faster than about 100 fs) with a branching ratio of a few percent. From the relaxed population in the S1 state, H-atom transfer yielding pyrimidinyl and hydroxyl radicals can occur on much longer time scales (picoseconds to nanoseconds) by H-atom tunneling.

Time-evolutions of excited state hydrogen transfer (ESHT) in phenol (PhOH)-(NH

We observe UV spectra of protonated dibenzylamine (dBAMH+) and its complexes with 15-crown-5 (dBAMH+–15C5), 18-crown-6 (dBAMH+–18C6), and 24-crown-8 (dBAMH+–24C8) under cold (~10 K) gas-phase conditions by UV photodissociation (UVPD) and UV-UV hole-burning (HB) spectroscopy. The UVPD spectrum of the dBAMH+–15C5 complex shows an extensive low-frequency progression, which originates from a unique conformation of the dBAMH+ part with benzene rings facing closely to each other, while UVPD and calculation results suggest open conformations of the dBAMH+ part for dBAMH+–18C6 and dBAMH+–24C8. UV-UV HB spectra of the dBAMH+–24C8 complex indicate that there exist at least two conformers; multiple conformations can contribute to high stability of dBAMH+–24C8 pseudorotaxane due to “conformational” entropic effects. The UVPD experiment indicates that the dissociation probability of dBAMH+–24C8 into dBAMH+ and 24C8 is substantially smaller than that of dBAMH+–15C5 and dBAMH+–18C6, which can be related to the barrier height in the dissociation process. The energetics of the dBAMH+–24C8 complex is investigated experimentally with NMR spectroscopy and theoretically with the global reaction route mapping (GRRM) method. An energy barrier of ~60 kJ mol–1 is present in the pseudorotaxane formation in solution, whereas there is no barrier in the gas phase. In the course of the photodissociation, excited dBAMH+–24C8 complexes can be trapped at many local minima corresponding to multiple conformations. This can result in effective dissipation of internal energy into degrees of freedom not correlated to the dissociation and decrease the dissociation probability for the dBAMH+–24C8 complex in the gas phase. The energy barrier for the pseudorotaxane formation in solution originates not simply from the slippage process but rather from solvent effects on the dBAMH+–24C8 complex., This work was partly supported by the JSPS KAKENHI Grant Number JP16H04098 and the MAEE/JSPS France-Japan Collaboration Program (SAKURA).

International audience; While aromatic amino acids in their deprotonated form have been well characterized by IR and photoelectron spectroscopies, no information is available on the neutral dehydrogenated protonated radicals and, in particular, on their stability when the deprotonation site is changed. This is investigated by observing the neutral fragment issued from either simple photodetachment or dissociative photodetachment of the deprotonated aromatic amino acids phenylalanine, tyrosine, and tryptophan. We show that the dehydrogenated radicals of aromatic amino acids produced upon photodetachment of molecules deprotonated on the carbonyl group dissociate without barrier, leading to the formation of CO 2 and a radical amine. However, when the system is deprotonated on functional groups located on the chromophore, the radicals produced by photodetachment are stable, indicating the important photostabilizing role played by functional groups.

International audience; The competition between dissociative photodetachment and photodissociation of cold benzoate and naphthoate anions was studied through measurement of the kinetic energy of the neutral fragments and intact parent benzoyloxy and naphtoyloxy radicals as well as by detecting the anionic fragments whenever they are produced. For the benzoate anion, there is no ionic photodissociation and the radical dissociation occurs near the vertical photodetachment energy. This is in agreement with DFT calculations showing that the dissociation energy in CO2 and C6H5˙ is very low. The dissociation barrier can be deduced from experimental results and calculations to be (0.7 ± 0.1) eV, which makes the benzoyloxyradical C6H5COO˙ very unstable, although more stable than the acetyloxy radical. In the case of naphthoate, the observation of negative fragments at low excitation energies demonstrates the opening of the ionic photodissociation channel in the excited state of the naphthoate anion, whose yield decreases at higher energies when the dissociative photodetachment channel opens.

In this chapter we will review the processes at play in the excited states of protonated molecules. More specifically, the discussion will be restricted to aromatic molecules, on which the majority of studies have been focused. Rather than going into details of each system, we will highlight the trends and general mechanisms that are involved in the excited state energy and dynamics. The interested reader can find detailed descriptions of each molecule in the individual publications. It appears that the excited state dynamics of many aromatic ions can be understood upon the application of rather elementary and universal concepts, the simplest of which being that the excited electron is attracted to the proton, triggering a large part of the excited state dynamics.

The fragmentation times corresponding to the loss of the chromophore (C$\alpha$-- C$\beta$ bond dissociation channel) after photoexcitation at 263 nm have been investigated for several small peptides containing tryptophan or tyrosine. For tryptophan-containing peptides, the aromatic chromophore is lost as an ionic fragment (m/z 130), and the fragmentation time increases with the mass of the neutral fragment. In contrast, for tyrosine-containing peptides the aromatic chromophore is always lost as a neutral fragment (mass = 107 amu) and the fragmentation time is found to be fast (\textless{}20 ns). These different behaviors are explained by the role of the postfragmentation interaction in the complex formed after the C$\alpha$--C$\beta$ bond cleavage.

The B̃

Excited-state hydrogen transfer (ESHT) is responsible for various photochemical processes of aromatics, including photoprotection of nuclear basis. Its mechanism is explained by internal conversion from the aromatic ππ* to πσ* states via conical intersection. This means that the electron is transferred to a diffuse Rydberg-like σ* orbital apart from proton migration. This picture means the electron and the proton do not move together and the dynamics are different in principle. Here, we have applied picosecond time-resolved near-infrared (NIR) and infrared (IR) spectroscopy to the phenol-(NH

International audience; TheHB1A1 HX1A1 electronic band system of the protonated diacetylene cation (H2C4H+) is measured over the 230–295 nm range by photodissociating H2C4H+ ions stored in a cryogenic iontrap and by photodissociating H2C4H+ tagged with Ar and N2 in a tandem mass spectrometer. The HB 1A1 HX1A1 band system has an origin at 34 941 cm1 for H2C4H+, 34 934 cm1 for H2C4H+–Ar,and 34 920 cm1 for H2C4H+–N2. The spectra of H2C4H+, H2C4H+–Ar, and H2C4H+–N2 display similar vibronic structure, which is assigned using ab initio calculations to progressions in two symmetric a1 C–C stretch vibrational modes (6 and 4), with band spacings of 860 and 1481 cm1, respectively.

Charge transfer reactions are ubiquitous in chemical reactivity and often viewed as ultrafast processes. For DNA, femtochemistry has undeniably revealed the primary stage of the deactivation dynamics of the locally excited state following electronic excitation. We here demonstrate that the full time scale excited state dynamics can be followed up to milliseconds through an original pump-probe photodissociation scheme applied to cryogenic ion spectroscopy. Protonated cytosine is chosen as a benchmark system in which the locally excited 1ππ∗ state decays in the femtosecond range toward long-lived charge transfer and triplet states with lifetimes ranging from microseconds to milliseconds, respectively. A three-step mechanism (1ππ∗ → 1CT → 3ππ∗) is proposed where internal conversion from each state can occur leading ultimately to fragmentation in the ground electronic state. Fil: Broquier, Michel. Université Paris Sud; Francia Fil: Soorkia, Satchin. Université Paris Sud; Francia Fil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Dedonder-Lardeux, Claude. Marseille Université; Francia Fil: Jouvet, Christophe. Marseille Université; Francia Fil: Grégoire, Gilles. Université Paris Sud; Francia

In aromatic systems that contain an amino group, there is competition between protonation on a carbon atom of the skeleton and protonation on the amino group. Herein, we studied the photofragmentation of protonated 1-aminopyrene in a cold ion trap and mainly observed the protonated amino tautomer, which led to fragmentation pathways through the loss of H or NH3 groups. Several excited states were assigned, among which the fourth excited state showed broadened bands, thus indicating a fast decay that was attributed to the presence of a πσ* charge-transfer state by comparison of the experimental results with ab initio calculations. We deduced the πσ* transition energies in protonated aromatic amino compounds of increasing size directly from the ionization potentials of the neutral aromatic unsubstituted molecules. Tautomers that were protonated on a carbon atom of the pyrene skeleton were also weakly observed, and we showed that two tautomers that were protonated on a carbon atom of the aromatic ring could be distinguished by using electronic spectroscopy.

Photofragmentation electronic spectra of isolated single-isomeric N-protonated quinoline (quinolinium) and isoquinoline (isoquinolinium) ions have been measured at a temperature of ∼40 K using a mass-selective, 10 cm-1 spectral resolution, photodissociation spectrometer. Additionally, ab initio adiabatic transition energies calculated using the RI-ADC(2) method have been employed to assist in the assignment of the spectra. Three electronic transitions having ππ∗ character were clearly evidenced for both protonated ions within the UV and deep-UV spectral ranges. The corresponding spectra at room temperature were previously reported by Hansen et al., together with TD-DFT calculations and a careful analysis of the possible fragmentation mechanisms. This information will be complemented in the present study by appending better resolved spectra, characteristic of cold ions, in which well-defined vibrational progressions associated with the S1 ← S0 and S3 ← S0 transitions exhibit clear 0-0 bands at hν0-0 = 27868 and 42230 cm-1, for protonated quinoline, and at hν0-0 = 28043 and 41988 cm-1, for protonated isoquinoline. Active vibrations in the spectra were assigned with the help of calculated normal modes, looking very similar to those of the structurally related protonated naphthalene. Finally, we have observed that the bandwidths associated with the deep-UV S3 ← S0 transition denote a lifetime for the S3 excited state in the subpicosecond time scale, in contrast with that of S1. Fil: Féraud, Géraldine. Aix-Marseille Université; Francia Fil: Domenianni, Luis Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Marceca, Ernesto José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Dedonder Lardeux, Claude. Aix-Marseille Université; Francia Fil: Jouvet, Christophe. Aix-Marseille Université; Francia

The photochemistry of ices with polycyclic aromatic hydrocarbons (PAHs) has been extensively studied, but to date no investigation has been made of PAHs in interaction with low numbers (n < 4) of molecules of water. We performed photochemical matrix isolation studies of coronene:water complexes, probing the argon matrix with FTIR spectroscopy. We find that coronene readily reacts with water upon irradiation with a mercury vapour lamp to produce oxygenated PAH photoproducts, and we postulate a reaction mechanism via a charge transfer Rydberg state. This result suggests that oxygenated PAHs should be widely observed in regions of the ISM with sufficiently high water abundances, for example near the edges of molecular clouds where water molecules begin to form, but before icy layers are observed, that is at AV, 5 pages, 5 figures, accepted for publication in A&A

Recently, DNA molecules have received great attention because of their potential applications in material science. One interesting example is the production of highly fluorescent and tunable DNA–Agn clusters with cytosine (C)-rich DNA strands. Here, we report the UV photofragmentation spectra of gas-phase cytosine···Ag+···cytosine (C2Ag+) and cytosine···H+···cytosine (C2H+) complexes together with theoretical calculations. In both cases, the excitation energy does not differ significantly from that of isolated cytosine or protonated cytosine, indicating that the excitation takes place on the DNA base. However, the excited-state lifetime of the C2H+ (τ = 85 fs), estimated from the bandwidth of the spectrum, is at least 2 orders of magnitude shorter than that of the C2Ag+ (τ > 5000 fs). The increased excited-state lifetime upon silver complexation is quite unexpected, and it clearly opens the question about what factors are controlling the nonradiative decay in pyrimidine DNA bases. This is an important result for the expanding field of metal-mediated base pairing and may also be important to the photophysical properties of DNA-templated fluorescent silver clusters. Fil: Berdakin, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Féraud, Geraldine. Aix Marseille Université. Marsella; Francia Fil: Dedonder Lardeux, Claude. Aix Marseille Université. Marsella; Francia Fil: Jouvet, Christophe. Aix Marseille Université. Marsella; Francia Fil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

A new ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopic scheme has been developed for cold gas phase ions in a quadrupole-ion-trap (QIT) connected with a time-of-flight (TOF) mass spectrometer. In this method, a pump UV laser generates a population hole for the ions trapped in the cold QIT and a second UV laser (probe) monitors the population hole for the ions extracted to the field free region of the TOF mass spectrometer. Here, the neutral fragments generated by the UV dissociation of the ions with the second laser are detected. This UV-UV HB spectroscopy was applied to protonated dibenzylamine and to protonated uracil. Protonated uracil exhibits two strong electronic transitions; one has a band origin at 31760 cm-1 and the other at 39000 cm-1. From the UV-UV HB measurement and quantum chemical calculations, the lower energy transition is assigned to the enol-keto tautomer and the higher energy one to the enol-enol tautomer., This study was supported in part by the France-Japan Collaboration Program (SAKURA) France, the Japan Society for Promotion of Science and the ANR Research Grant (ESPEM- ANR2010BLANC040501).

The electronic spectroscopy of protonated indole was investigated experimentally and theoretically. Two isomers have been observed in this experiment. The first isomer corresponds to the lowest energy isomer in the calculations, absorbing at ~350 nm and protonated on the C3 atom of the pyrrole ring. According to our calculations, the absorption of the other isomers protonated on carbon atoms is in the visible region. Indeed the second isomer observed absorbs in the blue (starting at 488 nm) and has been assigned to protonation on the C2 carbon of the pyrrole ring. Since good agreement was obtained between calculated and experimental transitions for the isomers observed, reasonable ab-initio transition energies may also be expected for the higher energy isomers protonated on carbon atoms, which should also absorb in the visible. Protonation on the nitrogen atom leads to a blue shifted transition. Fil: Aiata, Ivan. Centre Laser de L’université Paris Sud; Francia Fil: Bert, Johan. Aix-Marseille Université. Physique des Interactions Ioniques et Moléculaires; Francia Fil: Broquier, Michel. Centre Laser de L’université Paris Sud; Francia Fil: Dedonder, Claude. Aix-Marseille Université. Physique des Interactions Ioniques et Moléculaires; Francia Fil: Feraud, Géraldine. Aix-Marseille Université. Physique des Interactions Ioniques et Moléculaires; Francia Fil: Grégoire, Gilles. Université Paris 13, Sorbonne Paris Cité; Francia Fil: Soorkia, Satchin. Université Paris-Sud. Institut Des Sciences Moléculaires D’orsay; Francia Fil: Marceca, Ernesto José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de Los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires; Argentina Fil: Jouvet, Christophe . Aix-Marseille Université. Physique des Interactions Ioniques et Moléculaires; Francia

The gas phase structure and excited state lifetime of the p-aminophenol⋯p-cresol heterodimer have been investigated by REMPI and LIF spectroscopy with nanosecond laser pulses and pump-probe experiments with picosecond laser pulses as a model system to study the competition between p-p and H-bonding interactions in aromatic dimers. The excitation is a broad and unstructured band. The excited state of the heterodimer is long lived (2.5 ± 0.5) ns with a very broad fluorescence spectrum red-shifted by 4000 cm-1 with respect to the excitation spectrum. Calculations at the MP2/RI-CC2 and DFT-ωB97X-D levels indicate that hydrogen-bonded (HB) and p-stacked isomers are almost isoenergetic in the ground state while in the excited state only the p-stacked isomer exists. This suggests that the HB isomer cannot be excited due to negligible Franck-Condon factors and therefore the excitation spectrum is associated with the p-stacked isomer that reaches vibrationally excited states in the S1 state upon vertical excitation. The excited state structure is an exciplex responsible for the fluorescence of the complex. Finally, a comparison was performed between the p-stacked structure observed for the p-aminophenol. . .p-cresol heterodimer and the HB structure reported for the (p-cresol)2 homodimer indicating that the differences are due to different optical properties (oscillator strengths and Franck-Condon factors) of the isomers of both dimers and not to the interactions involved in the ground state. Fil: Capello, Marcela Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Hernández, Federico Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Broquier, Michel. Université Paris Sud; Francia Fil: Dedonder-Lardeux, Claude. Aix-Marseille Université; Francia Fil: Jouvet, Cristophe. Aix-Marseille Université; Francia Fil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

Gas phase photodissociation electronic spectra of protonated azobenzene (ABH+) and 4-(dimethylamino)azobenzene (dmaABH+) were measured in a cryogenically cooled ion trap at temperatures of a few tens of Kelvin. Experimental results were complemented with electronic structure calculations in the ground state at the MP2/cc-pVDZ level of theory, and in the low lying excited states using the RI-CC2 method. Calculated energies revealed that only the trans isomers of the azonium molecular ions (protonation site on the azo group) will likely exist in the trap at the temperatures achieved in the experiment. The first transition of trans-ABH+ is π∗ ← π, and the absorption band in the spectrum appears strongly red-shifted from that of the neutral molecule. The calculations showed that upon excitation the quasi-planar ground state (S0) transforms into a chairlike excited state (S1) by twisting the CNNC dihedral angle about 96°. A 41 cm-1 active vibrational progression found in the ABH+ spectrum may be associated with the twisting of the azo bond. Conversely, the electronic spectrum of dmaABH+ exhibits a steep and unstructured S1 ← S0 absorption corresponding to a less distorted S1 state. The next two quasi-degenerate bands in the ABH+ spectrum evidence sharper onsets and a charge transfer character. Using a second fragmentation laser and an additional He cooling pulse in the trap, it was possible to measure the UV spectrum of cold benzenediazonium fragments. Fil: Féraud, Géraldine. Centre National de la Recherche Scientifique; Francia. Aix-Marseille Universite; Francia Fil: Dedonder Lardeux, Claude. Centre National de la Recherche Scientifique; Francia. Aix-Marseille Universite; Francia Fil: Jouvet, Christophe. Centre National de la Recherche Scientifique; Francia. Aix-Marseille Universite; Francia Fil: Marceca, Ernesto José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

International audience; The excited state properties of protonated ortho (2-), meta (3-) and para (4-) aminopyridine molecules have been investigated through UV photo fragmentation spectroscopy and excited state couple cluster CC2 calculations. Cryogenic ion spectroscopy allows recording well-resolved vibronic spectroscopy that can be nicely reproduced through Franck Condon simulations of the pp* local minimum of the excited state potential energy surface. The excited state lifetimes have also been measured through a pump-probe excitation scheme and compared to the estimated radiative lifetimes. Although protonated aminopyridines are rather simple aromatic molecules, their deactivation mechanisms are indeed quite complex with unexpected results. In protonated 3-and 4-aminopyridine, the fragmentation yield is negligible around the band origin, which implies the absence of internal conversion to the ground state. Besides, a twisted intramolecular charge transfer reaction is evidenced in protonated 4-aminopyridine around the band origin, while excited state proton transfer from the pyridinic nitrogen to the adjacent carbon atom opens with roughly 500 cm-1 of excess energy.

International audience; Ab-initio calculations predict that pyridine (Py) can act as a photo-catalyst to split water by absorption of a UV photon following the reaction Py-H 2 O + hν → PyH● + OH●. To test this prediction, we performed two types of experiment: in the first, we characterize the electronic spectroscopy of the PyH● radical in the gas phase. In the second, we evidence the reaction through UV excitation of molecular Py-(H2O) n clusters obtained in a supersonic expansion and monitoring the PyH● reaction product. The results show unambigu-ously that PyH● is produced, thus that water is split using pyridine as photo-catalyst. In this paper we show that pyridine can act as a photo-catalytic molecular system, which can dissociate the water covalent bond with UV C light. Water molecule is a ubiquitous system to produce H2 , however VUV light is needed to photo-dissociate the H-OH covalent bond (186 nm, 6.66 eV). Since most of the sunlight reaching the earth is in the visible spectral region, we cannot dissociate the H-OH bond under normal sunlight conditions and it is necessary to design a system that could break the H-OH bond with visible light.

The excitation spectrum of protonated salicylaldehyde has been recorded in the 20,800–22,400 cm−1 region (480–450 nm). The first excited state of protonated salicylaldehyde is a ππ∗ state, largely red shifted as compared to the ππ∗ transition of its neutral analogue. Like protonated benzaldehyde and in contrast to some other protonated aromatic molecules such as benzene or tryptophan in which the excited state dynamics is so fast that no vibrational structure can be observed, the vibrational bands are well resolved and assigned. This molecule has many low energy isomers and the simulations of the electronic spectrum via ab initio excited state optimizations and Franck–Condon calculations are precise enough to assign the observed electronic spectrum to one of the isomers.

Electronic spectra of the S(1)←S(0) transition of dimers of protonated benzaldehyde (BZH(+)) with Ar and N(2) are recorded by resonance-enhanced photodissociation in a tandem mass spectrometer. The S(1) origins observed are shifted to higher frequency upon complexation with Ar (ΔS(1) = 300 cm(-1)) and N(2) (ΔS(1) = 628 cm(-1)). Ab initio calculations at the CC2/aug-cc-pVDZ level suggest an assignment to H-bonded dimers of L = Ar and N(2) binding to the cis isomer of O-protonated BZH(+), yielding values of ΔS(1) = 242 and 588 cm(-1) for cis-BZH(+)-L(H). Electronic ππ* excitation results in a substantial increase of the proton affinity of BZH(+), which in turn destabilizes the intermolecular H-bonds to the inert ligands by 35%. The drastic effects of electronic ππ* excitation on the geometric and electronic structure as well as the strength and anisotropy of the intermolecular potential (H-bonding and π-bonding) are investigated.

Because of its excellent diagnostic performance, whole-body MRI will probably become an alternative to or replacement for positron emission tomography and computed tomography (PET-CT). The sensitivity of diffusion sequences is high. Whole body MRI is used increasingly often in oncology, for initial or follow-up staging, finding primary tumors after identifying metastases, staging for pregnant woman and children, and therapeutic follow-up. Advantages of whole-body MRI over PET-CT include the absence of irradiation as well as the greater availability, and lower cost of MRI.

In the neurotransmission process, a specific neurotransmitter binds to a specific receptor in a “key and lock” recognition process. Neurotransmitters, such as the catecholamines, are flexible molecules that can change their shape easily in principle. However, conformations of both the “key” and “lock” must be quite limited to achieve high selectivity. We have investigated the conformational diversity of catecholamines and related molecules by laser spectroscopy. Molecules of the tyrosine family, which contain a phenolic aromatic chromophore, exist as several conformers. In contrast, a single conformer is observed in dopa and other catecholamines, which contain two hydroxyl groups on the benzene moiety (catechol). This demonstrates that the presence of a catechol ring restricts significantly the number of stable conformations.

We have investigated the excited-state multiple-proton/hydrogen atom transfer reactions in the 7-azaindole water clusters, [7AI](H(2)O)(n) (n = 2,3), in the gas phase by combining electronic spectroscopy and quantum chemical calculations. The fluorescence excitation (FE) spectrum of 7AI(H(2)O)(2) has been observed by monitoring visible emission. In contrast, no vibronic bands are detected in the FE spectrum of 7AI(H(2)O)(3) when the visible emission is monitored. The dispersed fluorescence spectra of 7AI(H(2)O)(n) (n = 2,3) have been measured. The excitation of +180 cm(-1) band from the electronic origin of 7AI(H(2)O)(2) enhances the visible emission as compared with the 0-0 excitation. The +180 cm(-1) band is assgined to an intermolecular mode (σ(1)) of the cyclic hydrogen-bonded ring structure. The calculated S(1)-S(0) absorption spectrum for the cyclic hydrogen-bonded structure is in agreement with the FE spectrum around the 0-0 region. The excitation of σ(1) significantly promotes the reaction and generates the tautomeric form of 7AI(H(2)O)(2). These experimental results on 7AI(H(2)O)(n) (n = 2,3) are very similar to those on 7AI(CH(3)OH)(n) (n = 2,3) and 7AI(C(2)H(5)OH)(n) (n = 2,3). We conclude that the excited-state triple proton/hydrogen atom transfer (ESTPT/HT) occurs in 7AI(H(2)O)(2). Cuts of the potential energy surfaces along the proton/hydrogen atom transfer coordinates of 7AI(H(2)O)(n) (n = 2,3) and 7AI(CH(3)OH)(n) (n = 2,3) are comparatively calculated by quantum chemistry calculations (RI-CC2/cc-pVDZ and TD-DFT(B3LYP)/cc-pVDZ) to explore the mechanism of the ESTPT/HT reaction. The calculated results suggest that concerted proton transfers occur in 7AI(H(2)O)(2) as well as in 7AI(CH(3)OH)(2), whereas the potential barrier for the excited-state quadruple proton transfer in 7AI(H(2)O)(3) and 7AI(CH(3)OH)(3) is higher than those for ESTPT. The theoretical results are consistent with the observation of ESTPT/HT in 7AI(H(2)O)(2).

Photofragmentation of protonated dipeptides by 263 nm photons is investigated with an experimental technique based on the detection in coincidence of the ionic and neutral fragments. With this method, it is possible to determine whether the fragmentation takes place in one or several steps. The timing of these steps can also be evaluated. The interpretation of the various fragmentation pathways is tentatively developed along the same line as that previously proposed for tryptophan. The fragmentation can be explained by two types of mechanisms: internal conversions and direct fragmentations triggered by the migration of the photoactive electron on positive charged sites or on oxygen sites.

Photodissociation of the complex between protonated tryptamine, TryH + , and 18-crown-6 ether (CE) was investigated. Absorption maxima of TryH + and TryH + (CE) are at 249 and 273 nm, respectively. Ions decay exponentially on a microsecond timescale, and mass spectra reveal that NH 3 loss is an important channel even though CE targets this group. TD-DFT calculations identified an electronically excited state, where the photoactive electron is located in an antibonding orbital between C and NH 3 . Dissociation along this coordinate and CE rearrangement to the new charge site accounts for ammonia loss. Photodissociation in an electric field and time-of-flight measurements corroborate such a non-statistical bond-breakage.

The structure of the calix[4]arene(C4A)-(H(2)O) cluster formed in a supersonic beam has been investigated by mass-selected resonant two-photon ionization (R2PI) spectroscopy, IR-UV double resonance spectroscopy, IR photodissociation (IRPD) spectroscopy and by high-level quantum chemical calculations. The IR-UV double resonance spectrum of C4A-(H(2)O) exhibits a broad and strong hydrogen-bonded OH stretching band at 3160 cm(-1) and a weak asymmetric OH stretching band at 3700 cm(-1). The IRPD measurement of the cluster produced a value of 3140 cm(-1) for the C4A-(H(2)O) --C4A + H(2)O dissociation energy. High-level electronic structure calculations at the MP2 level of theory with basis sets up to quadruple-zeta quality suggest that the endo-isomer (water inside the C4A cavity) is approximately 1100 cm(-1) more stable than the exo-isomer (water hydrogen bonded to the rim of C4A). The endo-isomer has a best-computed (at the MP2/aug-cc-pVQZ level) value of 3127 cm(-1) for the binding energy, just approximately 15 cm(-1) shy of the experimentally determined threshold and an IR spectrum in excellent agreement with the experimentally observed one. In contrast, the B3LYP density functional fails to even predict a stable structure for the endo-isomer demonstrating the inability of that level of theory to describe the delicate balance between structures exhibiting cumulative OH-pi H-bonding and dipole-dipole interactions (endo-isomer) when compared to the ones emanating from maximizing the cooperative effects associated with the formation of hydrogen bonded homodromic networks (exo-isomer). The comparison of the experimental results with the ones from high-level electronic structure calculations therefore unambiguously assign the endo-isomer as the global minimum of the C4A-(H(2)O) cluster, world's smallest cup of water.

The reaction paths in the lowest excited electronic states relevant for the photophysics of protonated benzene, C(6)H(7)(+), have been explored by ab initio techniques of electronic structure theory. For this purpose, the first four excited singlet electronic states of C(6)H(7)(+) have been calculated at the CC2/cc-pVTZ level of theory. The CC2 approach has been validated by CASPT2 and TD-DFT calculations. The calculated UV absorption spectrum is in good agreement with the experimental spectrum. It has been found that the out-of-plane and the in-plane ring deformation leads in the excited states in an essential barrierless manner to a low-lying conical intersection between the lowest excited states and with the ground state, providing a mechanism for efficient radiationless deactivation, which is expected to quench luminescence of the isolated molecular ion.

In recent experiments, the excited-state lifetimes of protonated aromatic amino acids (TrpH+ and TyrH+) have been recorded by means of pump-probe photodissociation technique. The lifetime of TyrH+ is much longer than that of TrpH+, which has been initially rationalized on the basis of a simple phenomenological model. Besides, specific photofragments including the formation of radical cation after hydrogen loss are observed for TrpH+ that are not found for TyrH+. The ab initio calculations reported here for TrpH+ and TyrH+ using a coupled-cluster method are meant to track the rich photochemistry of these protonated amino acids following UV excitation.

The gas phase structure and excited state dynamics of o-aminophenol-H2O complex have been investigated using REMPI, IR-UV hole-burning spectroscopy, and pump–probe experiments with picoseconds laser pulses. The IR-UV spectroscopy indicates that the isomer responsible for the excitation spectrum corresponds to an orientation of the OH bond away from the NH2 group. The water molecule acts as H-bond acceptor of the OH group of the chromophore. The complexation of o-aminophenol with one water molecule induced an enhancement in the excited state lifetime on the band origin. The variation of the excited state lifetime of the complex with the excess energy from 1.4 ± 0.1 ns for the 0–0 band to 0.24 ± 0.3 ns for the band at 0–0 + 120 cm–1 is very similar to the variation observed in the phenol-NH3 system. This experimental result suggests that the excited state hydrogen transfer reaction is the dominant channel for the non radiative pathway. Indeed, excited state ab initio calculations demonstrate that H transfer leading to the formation of the H3O• radical within the complex is the main reactive pathway. Fil: Hernández, Federico Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Capello, Marcela Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Naito, Ayumi. Tokyo Institute of Technology; Japón Fil: Manita, Shun. Tokyo Institute of Technology; Japón Fil: Tsukada, Kohei. Tokyo Institute of Technology; Japón Fil: Miyazaki, Mitsuhiko. Tokyo Institute of Technology; Japón Fil: Fujii, Masaaki. Tokyo Institute of Technology; Japón Fil: Broquier, Michel. Université Paris Sud; Francia Fil: Gregoire, Gabriel Eduardo. Université Paris Sud; Francia Fil: Dedonder Lardeux, Claude. Aix Marseille Université; Francia Fil: Jouvet, Christophe. Aix Marseille Université; Francia Fil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

International audience; The best determination of the most stable protonation site in aromatic molecule relies 5 nowadays on the IRspectroscopy and ab initio calculations. It appears that these methods are not necessarily unambiguousand cannot always be safely employed. We present in this paper an example showing that electronicspectroscopy of cold ions complemented with ab initio calculations gives clear results on the protonationsite. In the example given on the aminophenol isomers (in ortho, meta and para positions), the protonation10 site is assigned from the electronic spectroscopy and in particular we show that for the meta isomer theproton is not on the amino group as observed for the other isomers. It shows also that the protonation siteis not conserved in the electrospray evaporation/ ionization process.

The geometric and electronic structures of cold host-guest complex ions of crown ethers (CEs) in the gas phase have been investigated by ultraviolet (UV) fragmentation spectroscopy. As host CEs, we chose 15-crown-5 (15C5), 18-crown-6 (18C6), 24-crown-8 (24C8), and dibenzo-24-crown-8 (DB24C8), and as guests protonated-aniline (aniline•H+) and protonated-dibenzylamine (dBAM•H+) were chosen. The ions generated by an electrospray ionization (ESI) source were cooled in a quadrupole ion-trap (QIT) by cryogenic cooler, and the UV spectra were obtained by UV photodissociation (UVPD) spectroscopy. The UV spectroscopy was complemented by quantum chemical calculations of the most probable complex structures. The UV spectrum of aniline•H+•CE is very sensitive to the symmetry of CE; aniline•H+•18C6 shows sharp electronic spectrum similar to aniline•H+, while aniline•H+•15C5 shows very broad structure with poor Franck-Condon factors. In addition, a remarkable cage effect in the fragmentation process after UV excitation was observed in both complex ions. In the aniline•H+•CE complexes, the cage effect completely removed the dissociation channels of the aniline•H+ moiety. A large difference in the fragmentation yield between dBAM•H+•18C6 and dBAM•H+•24C8 was observed due to a large barrier for releasing dBAM•H+ from the axis of rotaxane in the latter complex., This study was supported in part by the France-Japan Collaboration Program (SAKURA), the Japan Society for Promotion of Science and the ANR Research Grant (ESPEM- ANR2010BLANC040501).

International audience; We present photo-fragmentation electronic spectra of the simplest protonated aromatic molecules, protonated benzene and toluene, recorded under medium resolution conditions and compared with the photo-fragmentation spectrum of protonated pyridine. Despite the resolution and cold temperature achieved in the experiment, the electronic spectra of protonated benzene and toluene are structure-less, thus intrinsically broadened. This is in agreement with the large geometrical changes and the fast dynamic toward internal conversion predicted by ab-initio calculations for protonated benzene (M. F. Rode, A. L. Sobolewski, C. Dedonder, C. Jouvet, and O. Dopfer, J. Phys. Chem. A 113, 5865–5873 (2009).

We are presenting the electronic photo fragment spectra of the protonated pyrimidine DNA bases homo-dimers. Only the thymine dimer exhibits a well structured vibrational progression, while protonated monomer shows broad vibrational bands. This shows that proton bonding can block some non radiative processes present in the monomer., We acknowledge the use of the computing facility cluster GMPCS of the LUMAT federation (FR LUMAT 2764)

Reprinted (adapted) with permission from Journal of Physical Chemistry A Copyright (2015) American Chemical Society; International audience; The electronic spectroscopy and the electronic excited state properties of cold protonated phenylalanine and protonated tyrosine have been revisited on a large spectral domain and interpreted by comparison with ab initio calculations. The protonated species are stored in a cryogenically cooled Paul trap, maintained at ~ 10K, and the parent and all the photo-fragment ions are mass-analyzed in a time-of-flight mass spectrometer, which allows detecting the ionic species with an improved mass resolution compared to what is routinely achieved with a quadrupole mass spectrometer. These new results emphasize the competition around the band origin between two proton transfer reactions from the ammonium group toward either the aromatic chromophore or the carboxylic acid group. These reactions are initiated by the coupling of the locally excited ππ* state with higher charge transfer states, the positions and coupling of which depend on the conformation of the protonated molecules. Each of these reaction processes gives rise to specific fragmentation channels that supports the conformer selectivity observed in the photofragmentation spectra of protonated Tyrosine and Phenylalanine.

The lifetimes of the 3-methylindole-NH3 complex have been measured on different vibronic levels involving intermolecular modes and decrease from 530 to 65 ps, in a mode specific manner. Geometry optimizations of the ground and excited states have been performed with ab initio methods, and as in the case of phenol and indole, a repulsive pi sigma* state lies close to the initially excited pi pi* state. From these calculations, it seems that both in-plane and out-of-plane vibrations induce a faster nonradiative decay.