Photofragmentation spectroscopy of cold protonated aromatic amines in the gas phase

The electronic spectroscopy of cold protonated aromatic amines, anilineH+ C6H5-NH3+, benzylamineH+ C6H5-CH2-NH3+ and phenethylamineH+ C6H5-(CH2)2-NH3+ has been investigated experimentally in a large spectral domain and is compared to that of their hydroxy- homologues (OH containing). In the low energy region, the electronic spectra are similar to their neutral analogues, which reveals that their first excited state is of * character. A second transition is observed from 0.5 to 1 eV above the origin band, which is assigned to the excitation of the * state. In these protonated amine molecules, there is a competition between different fragmentation channels, some of them being specific of the UV excitation and are not observed in low-energy collision induced dissociation experiment. Besides, a drastic change in the fragmentation branching ratio can be observed within a very short energy range that reveals the complex excited state dynamics and fragmentation processes in these species. The experimental observations can be rationalized with a simple qualitative model, the /* model(PCCP-2002), which predicts that the excited state dynamics is controlled by the crossing between the * excited state and a state repulsive along the XH (X being O or N) coordinate

Excited State Dynamics of Protonated Phenylalanine and Tyrosine: Photo-Induced Reactions Following Electronic Excitation

Reprinted (adapted) with permission from Journal of Physical Chemistry A Copyright (2015) American Chemical SocietyInternational audienceThe 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

Selective Tautomer Production and Cryogenic Ion Spectroscopy of Radical Cations: The Uracil and Thymine Cases

2 Year Impact Factor 2023: 2.7Fil: Molina, Franco L. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica. Centro Láser de Ciencias Moleculares, Argentina.Fil: Molina, Franco L. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-Química de Córdoba, Argentina.Fil: Molina, Franco L. Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d’Orsay, Orsay F-91405, FranceFil: Broquier, Michel. Université Paris-Saclay, CNRS. Institut des Sciences Moléculaires, France.Fil: Soorkia, Satchin. Université Paris-Saclay, CNRS. Institut des Sciences Moléculaires d’Orsay, France.Fil: Grégoire, Gilles. Université Paris-Saclay, CNRS. Institut des Sciences Moléculaires d’Orsay, France.Fil: Pino, Gustavo A. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica. Centro Láser de Ciencias Moleculares, Argentina.Fil: Pino, Gustavo A. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-Química de Córdoba, Argentina.Fil: Pino, Gustavo A. Université de Rennes. Institut de Physique de Rennes, France.The vibrational and electronic spectroscopy of the radical cations of two nucleobases (NB) (uracil and thymine) was studied by cryogenic ion photodissociation spectroscopy. The radical cations have been generated from the photodissociation of NB–Ag+ complexes. A charge transfer process from the NB to Ag+ governs the deactivation mechanism, leading to the formation of the radical cation without further tautomerization. Single- and double-resonance spectroscopy allows for structural assignments of both the silver complexes and the radical cations by comparison with DFT-based calculations. Interestingly, a tautomer-dependent fragmentation is observed in the thymine enol form that involves the loss of NCO, a fragment which was never reported before for this NB. This selective photodissociation of silver complexes containing aromatic chromophore greatly expands the current technique to produce isomer-selected radical cations in the gas phase providing benchmark experimental data to assess calculations of open-shell species.info:eu-repo/semantics/publishedVersionFil: Molina, Franco L. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica. Centro Láser de Ciencias Moleculares, Argentina.Fil: Molina, Franco L. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-Química de Córdoba, Argentina.Fil: Molina, Franco L. Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d’Orsay, Orsay F-91405, FranceFil: Broquier, Michel. Université Paris-Saclay, CNRS. Institut des Sciences Moléculaires, France.Fil: Soorkia, Satchin. Université Paris-Saclay, CNRS. Institut des Sciences Moléculaires d’Orsay, France.Fil: Grégoire, Gilles. Université Paris-Saclay, CNRS. Institut des Sciences Moléculaires d’Orsay, France.Fil: Pino, Gustavo A. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica. Centro Láser de Ciencias Moleculares, Argentina.Fil: Pino, Gustavo A. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-Química de Córdoba, Argentina.Fil: Pino, Gustavo A. Université de Rennes. Institut de Physique de Rennes, France

Hydrogen bonds vs. π-stacking interactions in the p-aminophenol⋯p-cresol dimer: an experimental and theoretical study

International audienceThe 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 excitedstate 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-oB97X-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 stat

Twisted Intramolecular Charge Transfer in Protonated Amino Pyridine

International audienceThe 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

Non-radiative processes in protonated diazines, pyrimidine bases and an aromatic azine

International audienceThe excited state lifetimes of DNA bases are often very short due to very efficient non-radiative processes assigned to the pp*–np* coupling. A set of protonated aromatic diazine molecules (pyridazine, pyrimidine and pyrazine C4H5N2+) and protonated pyrimidine DNA bases (cytosine, uracil and thymine), as well as the protonated pyridine (C5H6N+), have been investigated. For all these molecules except one tautomer of protonated uracil (enol–keto), electronic spectroscopy exhibits vibrational line broadening. Excited state geometry optimization at the CC2 level has been conducted to find out whether the excited state lifetimes measured from line broadening can be correlated to the calculated ordering of the pp* and np* states and the pp*–np* energy gap. The short lifetimes, observed when one nitrogen atom of the ring is not protonated, can be rationalized by relaxation of the pp* state to the np* state or directly to the electronic ground state through ring puckering

Electronic and vibrational spectra of protonated benzaldehyde-water clusters, [BZ-(H2O)n≤5]H+: evidence for ground-state proton transfer to solvent for n ≥ 3.

International audienceVibrational and electronic photodissociation spectra of mass-selected protonated benzaldehyde-(water)n clusters, [BZ-(H2O)n]H(+) with n ≤ 5, are analyzed by quantum chemical calculations to determine the protonation site in the ground electronic state (S0) and ππ(*) excited state (S1) as a function of microhydration. IR spectra of [BZ-(H2O)n]H(+) with n ≤ 2 are consistent with BZH(+)-(H2O)n type structures, in which the excess proton is localized on benzaldehyde. IR spectra of clusters with n ≥ 3 are assigned to structures, in which the excess proton is located on the (H2O)n solvent moiety, BZ-(H2O)nH(+). Quantum chemical calculations at the B3LYP, MP2, and ri-CC2 levels support the conclusion of proton transfer from BZH(+) to the solvent moiety in the S0 state for hydration sizes larger than the critical value nc = 3. The vibronic spectrum of the S1 ← S0 transition (ππ(*)) of the n = 1 cluster is consistent with a cis-BZH(+)-H2O structure in both electronic states. The large blueshift of the S1 origin by 2106 cm(-1) upon hydration with a single H2O ligand indicates that the proton affinity of BZ is substantially increased upon S1 excitation, thus strongly destabilizing the hydrogen bond to the solvent. The adiabatic S1 excitation energy and vibronic structure calculated at the ri-CC2/aug-cc-pVDZ level agrees well with the measured spectrum, supporting the notion of a cis-BZH(+)-H2O geometry. The doubly hydrated species, cis-BZH(+)-(H2O)2, does not absorb in the spectral range of 23 000-27 400 cm(-1), because of the additional large blueshift of the ππ(*) transition upon attachment of the second H2O molecule. Calculations predict roughly linear and large incremental blueshifts for the ππ(*) transition in [BZ-(H2O)n]H(+) as a function of n. In the size range n ≥ 3, the calculations predict a proton transfer from the (H2O)nH(+) solvent back to the BZ solute upon electronic ππ(*) excitation

Electronic excited state of protonated aromatic molecules: protonated Fluorene

The photo-fragmentation spectrum of protonated fluorene has been recorded in the visible spectral region, largely red shifted as compared to the first excited state absorption of neutral fluorene. The spectrum shows two different vibrational progressions, separated by 0.19 eV that are assigned to the absorption of two isomers. As in protonated linear PAHs, comparison with ab-initio calculations indicates that the red shift is due to the charge transfer character of the excited state

Trapped hydronium radical produced by ultraviolet excitation of substituted aromatic molecule

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; ArgentinaFil: 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; ArgentinaFil: Naito, Ayumi. Tokyo Institute of Technology; JapónFil: Manita, Shun. Tokyo Institute of Technology; JapónFil: Tsukada, Kohei. Tokyo Institute of Technology; JapónFil: Miyazaki, Mitsuhiko. Tokyo Institute of Technology; JapónFil: Fujii, Masaaki. Tokyo Institute of Technology; JapónFil: Broquier, Michel. Université Paris Sud; FranciaFil: Gregoire, Gabriel Eduardo. Université Paris Sud; FranciaFil: Dedonder Lardeux, Claude. Aix Marseille Université; FranciaFil: Jouvet, Christophe. Aix Marseille Université; FranciaFil: 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; Argentin

Processus inelastiques rotationnels induits par collisions dans des molecules interstellaires : OCS et NH3

SIGLECNRS T 57590 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc