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By the straightforward incorporation of an enamine group as an electron-donor moiety at meso position of BODIPY core, a halogen-free theragnostic photosensitizer for PDT with ability of bio staining lipid droplets is achieved.

We have conducted time-resolved experiments (pump–probe and pump–repump–probe) on a model aromatic chromophore, aniline, after excitation in water at 267 nm. In the initial spectra recorded, in addition to the absorption corresponding to the bright ππ* excitation, the fingerprint of a transient state with the electron located on the solvent molecule is identified. We postulate that the latter corresponds to the πσ* state along the N–H bond, whose complete relaxation with a ∼500 ps lifetime results in the formation of the fully solvated electron and cation. This ionization process occurs in parallel with the ππ* photophysical channel that yields the characteristic ∼1 ns fluorescence lifetime. The observed branched pathway is rationalized in terms of the different H-bonds that the water establishes with the amino group. The proposed mechanism could be common for aromatics in water containing N–H or O–H bonds and would allow the formation of separated charges after excitation at the threshold of their electronic absorptions.

The search for efficient heavy atom free photosensitizers (PSs) for photodynamic therapy (PDT) is a very active field. We describe herein a simple and easily accessible molecular design based on the attachment of an enamine group as an electron-donor moiety at the

EnglishThe educational community is aware of the importance of Human Rights Education for an inclusive society. Thus, the knowledge of theses inviolable rights is essential, and students should be aware of their violation. Starting from the objective of a true democratic society, we must avoid such attitudes, denouncing them and looking for possible solutions. In summary, Human Rights Education seeks to create critical human groups and individuals by making our students active, participatory and transformative citizens, in order to facilitate civic coexistence. For this end, the students of the Faculty of Education of Vitoria-Gasteiz carried out an introductory analytical task within Adi-Adian module, where they put in contact the different civil, social, cultural and political Human Rights and the reality, developing part of the objectives and contents of the Social and Civic Competence satisfactorily. Furthermore, the students will reflect about this learning process through a co-assessment task, which shows positive results euskaraAspalditik Giza Eskubideetarako Hezkuntzaren garrantziaz jabetu gara hezkuntza-komunitatean. Hori horrela, pertsona orori gizaki izateagatik dagozkion eskubide bortxaezinen ezagutza ezinbestekoa da, eta ikasleei gizartean gertatzen diren eskubideen urraketez ohartarazi behar zaie. Benetako berdintasunean oinarritutako gizarte demokratikoa helburutzat izanda, horrelako jarrerak ekidin beharrean gaude, horiek salatuz eta horiei aurre egiteko irtenbideak bilaraziz. Azken finean, Giza Eskubideetarako Hezkuntzaren bidez gizabanako eta gizatalde kritikoak sortu nahian gaude, gure ikasleak herritar aktiboak, parte-hartzaileak eta eraldatzaileak bilakatuz eta bizikidetza erraztuko duten subjektuak sorraraziz. Horretarako, Gasteizko Hezkuntza Fakultateko ikasleekin hasierako praktika analitiko bat egin da Adi-Adian moduluaren barnean, non Giza Eskubideen Aldarrikapen Unibertsalaren eskubide zibil, politiko, sozial eta kulturalak egungo berriekin harremanetan jarri diren; bide batez, Konpetentzia Sozial eta Zibikoa garatu eta ikasleak Giza Eskubideetarako Hezkuntzaren praktikotasunaz jabetu dira. Bestalde, koebaluazio-ariketa baten bidez, ikasleek ikaskuntza-prozesu honi buruzko hausnarketa egin dute, eta emaitza positiboak lortu.

Laser spectroscopy in jets is one of the main sources of structural data from molecular aggregates. Consequently, numerous and sophisticated experimental systems have been developed to extract precise information, which is usually interpreted in the light of quantum mechanical calculations. However, even with the most sophisticated experiments, it is sometimes difficult to interpret the experimental results. We present here the example of water dimer and how after almost 70 years, the assignment of its mass-resolved IR spectrum still generates controversy that extends toward the mechanism of ionization of water aggregates.

This study describes a simple method to generate sub-20 fs UV-pulses (264 nm) by third-harmonic generation, in an air-plasma filament formed after focusing the fundamental 800 nm beam directly in the lab open-atmosphere. The generated pulses are applied to track the relaxation through the conical intersection that couples the S2 and S1 states, in the benchmark molecule of naphthalene. The transients, with a resolution of about 25 fs, show two differentiate patterns of quantum beats. The assignation of these oscillations to specific modes in the lower S1 state and to electronic coherence between the two coupled states is discussed. All the experiments were carried out at the CLPU facility. The authors acknowledge the assistance from the CLPU technical and administrative personnel. They also thank the financial support from the Spanish MINECO through the grant: PGC2018-098561-B-C21. The work was also funded by the Basque Government (IT1162-19 and IT1491-22). I. Lamas thanks the UPV/EHU for his predoctoral fellowship. Technical and human support provided by SGIker (UPV/EHU, MICINN, GV/EJ, ESF) is also gratefully acknowledged. The authors greatly appreciate the Open Access funding provided by University of Basque Country.

Aiming to serve as a guide to understand the relaxation mechanisms of more complex aza-aromatic compounds, such as purine bases, we have studied the non-radiative channels of a set of azaindole structural isomers: 4-, 5-, 6- and 7-azaindole (AI). The relaxation of the isolated molecules, after excitation at the low energy portion of their spectra, has been tracked by femtosecond time-resolved ionization, and the decay paths have been obtained with MS-CASPT2//TD-DFT calculations. Although the ultrashort measured lifetimes for 5- and 6-AI are in contrast to the long-living excited state found in 7-AI, the calculations describe a common relaxation pathway. Along it, the initially excited ππ* states decay to the ground state through a conical intersection accessed through an nπ* state that functions as a gate state. The work reveals that the position of the nitrogen atoms in the purine ring determines the barrier to access the gate state and therefore, the rate of the non-radiative relaxation.

The available experimental data provided by ultrafast dynamics studies of pyrrole and its derivatives in excited states of mixed Rydberg/valence 3s/πσ* character are strongly affected by the interaction with the laser pulses. Understanding these data has constituted an endeavor for several groups during the past few years. Here we apply a simple theoretical model that, including the interaction with the laser pulses, allows one to clarify some aspects of the discrepancies between measurements monitoring different experimental observables. New experimental data on pyrrole, 2,4-dimethylpyrrole, and 2,5-dimethylpyrrole are also provided to check the validity of the model and to gain more insight into the excited state dynamics of pyrrole systems.

The use of genetic tests in assisted reproduction is growing fast. Among potential usages, the selection of the most suitable donor profile stands out. Being able to consider the genomic compatibility between donor and recipient is very important in order to prevent certain diseases. Nevertheless, taking this new factor into account can significantly increase the time needed for donor selection. This paper describes a web-tool designed to automatize the comparison of genomic and phenotypic profiles in assisted reproduction practices, which potentially reduces the chance of error and the time needed in donor-matching processes.

We have investigated the relaxation, following excitation in the 290–235 nm region, of neutral aniline homoclusters (An)n formed in a supersonic expansion by femtosecond time resolved ionization. The applied method permits isolation of the dynamics of the dimer from that originated in bigger species of the generated distribution. Interestingly, and differently from the monomer and (An)n≥3 clusters, the dimer does not present a N–H dissociative 1πσ* channel. This fact can be explained in terms of the symmetric structure adopted, in which each molecule establishes two N–H⋯π interactions, destabilizing the H dissociation channel. The observations permit relating the photophysics to the interactions established by the aniline units and confirming previous observations and theoretical predictions on the structure of aniline aggregates.

The photoprotective capabilities of a family of compounds have been investigated. Their relaxation mechanisms have been explored by fluorescence and transient absorption measurements, and the minimum energy relaxation pathways were modeled by CASSCF/CASPT2 methods. This study demonstrates their excellent properties as sunscreens, and provides novel mechanistic insights for the rational design of new species.

The relaxation dynamics of thiophenol, excited from the onset of the S 1 (1 1 ππ ∗ ) state absorption, to the more intense S 3 (2 1 ππ ∗ ) state band (290–244 nm), has been studied by time resolved ion yield spectroscopy. Along the studied energy range, the reached excited states relax in less 100 fs. These results evidence that the photophysics is dominated by the non-adiabatic coupling between the initially excited S 1 and S 3 1 ππ ∗ states, and the dissociative character 1 πσ ∗ state. Contrarily to phenol, the 1 1 ππ ∗ / 1 πσ ∗ crossing is reached from the origin of the 1 1 ππ ∗ state absorption, through a nearly barrierless pathway.

The photodynamics of an orthogonal BODIPY dimer, particularly the formation of triplet states, has been explored by femtosecond and nanosecond transient absorption measurements. The short time scale data show the appearance of transient features of triplet character that, according to quantitative analysis of their intensities, account for more than 100% of the initially excited molecules, which reveals the occurrence of a singlet fission process in the isolated dimers. The formation rate of the triplet correlated state (TT) is found to depend on the solvent polarity, pointing to the mediation of a charge transfer character state. The dissociation of the (TT) state into pairs of individual triplets determines the triplet yield measured in the long time scales. The kinetic model derived from the results provides a comprehensive view of the photodynamics of BODIPY dimers and permits rationalization of the photophysical parameters of these systems.

Método para caracterización de un pulso ultracorto, que comprende: hacer llegar un pulso de referencia de duración conocida a un primer detector con una banda prohibida menor que la energía por fotón del pulso a caracterizar y a un segundo detector con una banda prohibida mayor que la energía por fotón del pulso a caracterizar y menor que dos veces la energía por fotón del pulso a caracterizar: obtener en dicho primer detector una señal monofotónica de referencia Salref proporcional a la duración del pulso de referencia: obtener en dicho segundo detector una señal bifotónica de referencia beref proporcional a la duración del pulso de referencia; hacer llegar a los detectores un pulso ultracorto a caracterizar; obtener en dicho primer detector una señal monofotónica Sal proporcional a la duración del pulso ultracorto a caracterizar; obtener en dicho segundo detector una señal bifotónica Sbe proporcional a la duración del pulso ultracorto a caracterizar; obtener la duración del pulso a caracterizar a partir de dichas señales monofotónicas, de dichas señales bifotónicas y de la duración conocida del pulso de referencia. Dispositivo para la caracterización de un pulso ultracorto, Universidad del País Vasco - Euskal Herriko Unibertsitatea, Universidad de Cantabria, Consejo Superior de Investigaciones Científicas (España), A1 Solicitud de patente con informe sobre el estado de la técnica

Micelles are interesting self-organized structures with multiple applications in chemistry and related with the formation of biological structures. Their final shape depends on a subtle equilibrium between several weak forces: namely, van der Waals and hydrogen bond interactions. In order to address the influence of each type of interaction, the aggregation of cyclohexanol molecules was studied in the gas phase. The geometry of the clusters formed with sizes from 2 to 6 cyclohexanol molecules was elucidated by an IR double resonance technique that combines fs and ns lasers. Comparison of the structures obtained with those from previous studies demonstrates that hydrogen bond plays a central role in defining the general shape, but that its contribution to the overall stabilization energy may be lower than expected in systems with multiple C-H···π interactions.

The photochemical and photophysical pathways operative in N-methylpyrrole, after excitation in the near part of its ultraviolet absorption spectrum, have been investigated by the combination of time-resolved total ion yield and photoelectron spectroscopies with high-level ab initio calculations. The results collected are remarkably different from the observations made for pyrrole and other aromatic systems, whose dynamics is dictated by the presence of πσ* excitations on X–H (X: N, O, S, ...) bonds. The presence of a barrier along the C–N dissociation coordinate that can not be tunneled triggers two alternative decay mechanisms for the S1 A″ πσ* state. While at low vibrational content the C–N dissociation occurs on the surface of a lower 3ππ* state reached after efficient intersystem crossing, at higher excitation energies, the A″ πσ* directly internally converts to the ground state through a ring-twisted S1/S0 conical intersection. The findings explain previous observations on the molecule and may be relevant for more complex systems containing similar C–N bonds, such as the DNA nucleotides This work was funded by the “Ayudas para apoyar las actividades de grupos de investigación del sistema universitario vasco” program from the Basque Government, Grant 2014SGR1202 from the Agència de Gestiód’Ajuts Universitaris i de Recerca (AGAUR) from Catalonia (Spain), CTQ2016-69363-P from the Spanish Ministerio de Economıá y Competitividad (MINECO) and UNGI10-4E-801 from the Ministerio de Ciencia e Innovación (MICINN) and the European Fund for Regional Development, and the Xarxa de Refereǹ cia en Quiḿ ica Teor̀ ica i Computacional de Catalunya (AGAUR)

Mass-resolved excitation spectroscopic techniques are usually limited to systems with a chromophore, that is, a functional group with electronic transitions in the Vis/UV, with lifetimes from hundreds of picoseconds to some microseconds. In this paper, we expand such techniques to any system, by using a combination of nanosecond IR pulses with nonresonant ionization with 800 nm femtosecond laser pulses. Furthermore, we demonstrate that the technique can achieve conformational specificity introducing an additional nanosecond IR laser. As a proof-of-principle, we apply the technique to the study of phenol(H(2)O)(1), propofol(H(2)O)(1) γ-butyrolactone(H(2)O)(n), n = 1-3, and (H(2)O)(2) complexes. While monohydrated phenol and propofol clusters permit a direct comparison with a well-studied system including an aromatic chromophore, γ-butyrolactone is a cyclic nonaromatic molecule, whose mass-resolved spectroscopy cannot be tackled by conventional techniques. Finally, we further demonstrate the potential of the technique by obtaining the first mass-resolved IR spectrum of the neutral water dimer, a nice example of a system whose ionization-based detection had not been possible to date.

Global warming is likely to profoundly influence future weather patterns, and one consequence of this is the likelihood of an increase in tropical cyclone intensity. The present paper presents a cost-benefit analysis of introducing significant amounts of green energy in the electricity system in Japan in the light of the economic damage that an increase in tropical cyclone intensity could have on GDP growth between 2010 and 2085. Essentially the passage of a tropical cyclone will result not only in physical damage but also on a decrease in economic productivity due to precautionary cessation of the economic activity, which has an effect on GDP growth. By comparing the economic performance of different electricity system scenarios with the indirect economic damage of tropical cyclones from 2010 to 2085, based on the yearly economic data of green electricity, fossil fuel, GDP and population, it can be seen that the green scenarios are generally a cost-effective way of mitigating the effects of these weather systems, despite the large amount of initial investments necessary.

The influence of water solvation on the photophysics of the indole chromophore has been investigated by revisiting the ultrafast relaxation of indole–water clusters. The dynamics after excitation in the 284–234 nm energy range has been tracked by time delayed ionization with a 1305 nm probe. The results collected in the indole– ( H 2 O ) 1 + mass channel, which were ascribed mainly to the indole– ( H 2 O ) 2 + cluster fragmented by dissociative ionization, reflect a dynamical behavior analogous to that observed for the isolated indole molecule. The two femtosecond time constants observed in the transients were assigned to the coupling between the L a and L b π π ∗ surfaces, and to the system evolution along the dissociative π σ ∗ state.

The relaxation dynamics of the isolated indole molecule has been tracked by femtosecond time-resolved ionization. The excitation region explored (283-243 nm) covers three excited states: the two ππ* L(b) and L(a) states, and the dark πσ* state with dissociative character. In the low energy region (λ273 nm) the transients collected reflect the absorption of the long living L(b) state. The L(a) state is met 1000-1500 cm(-1) above the L(b) origin, giving rise to an ultrafast lifetime of 40 fs caused by the internal conversion to the lower L(b) minimum through a conical intersection. An additional ~400 fs component, found at excitation wavelengths shorter than 263 nm, is ascribed to dynamics along the πσ* state, which is likely populated through coupling to the photoexcited L(a) state. The study provides a general view of the indole photophysics, which is driven by the interplay between these three excited surfaces and the ground state.

A number of scientists have recently conducted research that shows that tropical cyclone intensity is likely to increase in the future. This would result in an increase in the damage along with a decrease in economic productivity due to precautionary cessation of the economic activity of the affected areas during the passage of the cyclone. The economic effect of this stop in economic activity is a phenomenon that has not received much attention in the past, and the cumulative effect that it can have on the Japanese economy over the next 75 years has never been evaluated. The starting point for the evaluation of the economic risks is the change in the patterns of tropical cyclone intensity suggested by Knutson and Tuleya.(1) The results obtained show how a significant decrease in the overall productivity of the country could be expected, which could lower GDP by between 6% and 13% by 2085.

An experimental study of the evolution of nanosecond pulsed lasers absorbed by Ni metal is presented. The ions ejected near fluence threshold fit single Maxwell–Boltzmann distributions (MBDs) whereas the ion distributions at higher fluences have side-bands whose maxima match accurately those of the ionization and recombination precursors. It is demonstrated that ions are trapped for ≈1 μs and further ejected in a few picoseconds whereas electrons have shorter dead time (≈10 ns) and continue evaporating for as long as ≈1 μs. Radiation is partially trapped during the creation of the electric field that ejects ions. The evolution also applies to other metals.

The relaxation dynamics of naphthalene (NPH) and 1-aminonaphthalene (AMN) in superexcited (SE) states has been investigated by pump-probe femtosecond ionization. SE states were produced by two-photon resonant absorption via S1 and S2 states and their time evolution probed by ionization with 800 nm light pulses. A fine-tuning of the pump and probe laser intensities permits us to separate the dynamics of the SE states from that of the S1/S2 intermediate states. SE state relaxation pathways were investigated in the channels of the parent and the major fragment ions. The lifetimes of two relaxation processes were derived from the exponential fit and found to be in the femtosecond and the picosecond time scales. The fast component is attributed to internal conversion (IC) from the SE states to the Rydberg states, whereas the slow one, only observed in the fragment transients, is assigned to fragmentation of the relaxed neutral molecules. The study sheds light on the significant role of SE states dynamics in pump-probe ionization experiments.

The relaxation dynamics of jet cooled naphthalene (NPH) has been studied by mass-resolved transient ionization, following excitation to the S 1 (L b ) and S 2 (L a ) states and further single/multi photon ionization at a variety of probe wavelengths. Time-dependent signals were collected from the parent C 10 H 8 + and the C 10 H 7 + fragment ions. The relaxation transients include two lifetimes of 30 and 800 fs. The short decay suggests the presence of a conical intersection nearby the L a state surface minimum that is crossed in one single passage by most part of the population, whereas the long lifetime is tentatively assigned either to internal vibrational redistribution (IVR) within the L b state, or to the decay of coherent recurrences.

A detailed investigation on the ion kinetic energy distributions of ions ejected in the nanosecond pulsed laser ablation of aluminum is reported. For laser fluences just over threshold, the emerging ions fit shifted neat Maxwell−Boltzmann-Coulomb (MBC) distributions. For fluences higher than ∼1.3 J/cm2, the Al+ distributions split into two MBC contributions peaked at different energies. It is demonstrated that the observed Al+ ion distribution has two components, one fast, correlated with the direct multiphoton laser ionization, and the other slow, associated with electron−Al0 collisions in the solid. A similar behavior is observed at higher fluences for all Al ion distributions indicating that the electron-impact ionization of Al rate constants is faster than that of recombination and other possible collision channels. In addition, the linear relationship between the Coulomb velocities and the ion charges and the behavior of Coulomb energy of the ions versus the laser fluence suggest the appearance of an...

The transient signals derived from femtosecond pump-probe experiments are analyzed in terms of the coherent evolution of the energy levels perturbed by the excitation pulse. The model system is treated as the sum of independent two-level subsystems that evolve adiabatically or are permanently excited, depending on the detuning from the central wavelength of the excitation laser. This approach will allow us to explain numerically and analytically the convergence between the coherent and incoherent (rate equations) treatments for complex multi-level systems. It will be also shown that the parameter that determines the validity of the incoherent treatment is the distribution of states outside and inside the laser bandwidth, rather than the density of states as it is commonly accepted., Comment: 11 pages. 8 Figures

The nonradiative relaxation channels of gas-phase tryptophan excited along the S1–S4 excited states (287–217 nm) have been tracked by femtosecond time-resolved ionization. In the low-energy region, λ ≥ 240 nm, the measured transient signals reflect nonadiabatic interactions between the two bright La and Lb states of ππ* character and the dark dissociative πσ* state of the indole NH. The observed dynamical behavior is interpreted in terms of the ultrafast conversion of the prepared La state, which simultaneously populates the fluorescent Lb> and the dissociative πσ* states. At higher energies, after excitation of the S4 state, the tryptophan dynamics diverges from that observed in indole, pointing to the opening of a relaxation channel that could involve states of the amino acid part. The work provides a detailed picture of the processes and electronic states involved in the relaxation of the molecule, after photoexcitation in the near part of its UV absorption spectrum.

The relaxation of 2,5-dimethylpyrrole after excitation in the 290-239 nm range, which covers the weak absorption of the S1 (1)A2 πσ* state, dissociative along the N-H bond, and the stronger band mostly attributed to the (1)B2 ππ* state, has been investigated by time-resolved ion and photoelectron techniques. The measurements yield an invariant lifetime of ∼55 fs for the (1)πσ* state, after preparation in its Franck-Condon region with increasing vibrational content. This ultrafast rate indicates that, contrary to the observations made in pyrrole (Roberts et al. Faraday Discuss. 2013, 163, 95-116), the molecule reaches the dissociative part of the potential without any barrier effect, although calculations predict the latter to be higher than in the pyrrole case. The results are rationalized in terms of a barrier free multidimensional pathway that very likely involves out-of-plane vibrations. Additionally, a lifetime of ∼100 fs is found after excitation along the higher (1)B2 ππ* ← S0 transition. The relaxation of this state by coupling to a very short living S1 (1)πσ* state, or by alternative routes, is discussed in the light of the collected photoelectron measurements.

Universities have increasingly emphasized competencies as central elements of students' development. However, the assessment of these competencies is not an easy task. The availability of data that learners generate in computer mediated learning offers great potential to study how learning takes place, and thus, to gather evidences for competency-assessment using enriched rubrics. These are the so-called electronic assessment instruments. Among them, the enriched rubrics arises as a tool to improve the assessment process. However, the lack of data interoperability and the decentralization of those educational applications set out a challenge to exploit trace data. To face these problems we have designed and developed SCALA (Supporting Competency-Assessment through a Learning Analytics approach), an analytics system that integrates usage -how the user interacts with resources- and social -how students and teachers interact among them- trace data to support competency assessment. After presenting the components of SCALA (process, model and platform), we evaluate them presenting six scenarios to know whether it is viable in terms of time, sustainability and quality assurance to normalize the heterogeneous data present in technology-rich learning environments. The results show and confirm the viability of the proposed solution and the possibility to offer real-time feedback to the teachers to assess students'.

2-Colour REMPI and ZEKE-PFI spectra of the 4-amino-3-ethylbenzonitrile (EtABN) molecule are reported for the first time. EtABN S 1 ← S 0 0 0 0 transition is located at 33 578 cm −1 , and its adiabatic ionisation threshold, as determined by ZEKE-PFI spectroscopy is 64 799 ± 4 cm −1 . A comparison with the spectra of 4-aminobenzonitrile (ABN) shows that the ethyl substituent gives rise to a rich spectroscopy, mainly involving the Ph–Et rocking mode.

The adiabatic ionization threshold (AIT) of trans- and gauche-benzocaine has been measured by zero electron kinetic energy-pulsed field ionization (ZEKE-PFI) spectroscopy to be 7.8412+/-0.0008 eV (lasers at 34,134.4 and 29,109.3 cm(-1)) and 7.8421+/-0.0004 eV (34,144.8+29105.7 cm(-1)), respectively. AITs computed at the B3LYP/AUG-cc-p-VDZ level for the two conformers are some approximately 2,500 cm(-1) lower than the experimental; in contrast their energy difference is very close. The trans-benzocaine cation ZEKE spectra has been recorded taking a number of S(1) intermediate vibronic states. The spectra provide an energy threshold for the appearance of intramolecular vibrational redistribution (IVR) around approximately 540 cm(-1) in the S(1) state.

The conformational isomerization dynamics of melatonin and 5-methoxy N-acetyltryptophan methyl amide (5-methoxy NATMA) have been studied using the methods of IR-UV hole-filling spectroscopy and IR-induced population transfer spectroscopy. Using these techniques, single conformers of melatonin were excited via a well-defined NH stretch fundamental with an IR pump laser. This excess energy was used to drive conformational isomerization. By carrying out the infrared excitation early in a supersonic expansion, the excited molecules were re-cooled into their zero-point levels, partially re-filling the hole created in the ground state population of the excited conformer, and creating gains in population of the other conformers. These changes in population were detected using laser-induced fluorescence downstream in the expansion via an UV probe laser. The isomerization quantum yields for melatonin show some conformation specificity but no hint of vibrational mode specificity. In 5-methoxy NATMA, no isomerization was observed out of the single conformational well populated in the expansion in the absence of the infrared excitation. In order to study the dependence of the isomerization on the cooling rate, the experimental arrangement was modified so that faster cooling conditions could be studied. In this arrangement, the pump and probe lasers were overlapped in space in the high density region of the expansion, and the time dependence of the zero-point level populations of the conformers was probed following selective excitation of a single conformation. The analysis needed to extract isomerization quantum yields from the timing scans was developed and applied to the melatonin timing scans. Comparison between the frequency and time domain isomerization quantum yields under identical experimental conditions produced similar results. Under fast cooling conditions, the product quantum yields were shifted from their values under standard conditions. The results for melatonin are compared with those for N-acetyl tryptophan methyl amide.

Author Institution: Department of Chemistry, Purdue University; Department of Chemistry and the James Franck Institute, University of Chicago

The 4-aminobenzonitrile (ABN) molecule has two active sites amenable to hydrogen bonding to methanol (MeOH) and ethanol (EtOH): the amino, –NH2, and the cyano, –CN, groups. Two-color resonance enhanced multiphoton ionization time-of-flight mass spectroscopy and hole burning spectroscopy in addition to the ionization energies provides sound evidence of the occurrence of two isomers in the ABN(MeOH)1 complex and one single isomer for the ABN(EtOH)1 complex. Combining the outcomes from the ABN/methanol and ABN/ethanol experiments with ab initio computations at reliable theory levels one identifies the preferred solvation sites and the optimized geometries. A discussion of the role of the aliphatic chains on the geometry of the isomers and other properties is presented.

The electronic and infrared spectra of anthranilic acid in a supersonic jet were measured. The fluorescence excitation spectrum is extremely congested. IR−UV hole-burning measurements indicate that only a single ground-state rotamer contributes to the observed spectrum. Vibrational progressions in 252 and 418 cm-1 modes were observed. Density functional theory calculations indicate that these modes involve the in-plane bending motions of the amino and carboxyl groups of anthranilic acid. The presence of vibrational progressions in these modes suggests that the relative positions of the amino and carboxyl groups are different in the ground and excited electronic states of anthranilic acid. This observation is supported by the fluorescence-dip infrared spectra acquired, which show a shift in the lower frequency NH stretch fundamental from 3394 to 2900 cm-1 upon electronic excitation, suggesting a dramatic strengthening of the intramolecular hydrogen bond in the excited state. The change in the hydrogen-bond...

This work reports the identification of the gas phase amino-p-phenethylamine (APEA) conformers with computed DFT stable structures. Two-colour mass-resolved multiphoton ionisation and hole burning spectroscopies have been used to find the number of conformers and record their spectra. The spectra show the presence of four well-characterized conformers, with origin bands paired off as gauche and anti conformers, in clear contrast to the five stable structures predicted by computational methods. Several criteria have been employed to relate the experimental spectra of the conformers to stable computed structures, the ionisation energies being the most reliable for unambiguous identification. The method can be applied to other small- and medium-size biological and organic molecules.

Herein, the interpretation of the femtosecond-scale temporal evolution of the pyrrole ion signal, after excitation in the 267-217 nm interval, recently published by our group [R. Montero, A. Peralta Conde, V. Ovejas, M. Fernández-Fernández, F. Castaño, J. R. Vázquez de Aldana, and A. Longarte, J. Chem. Phys. 137, 064317 (2012)] is re-visited. The observation of a shift in the pyrrole(+) transient respect to zero delay reference, initially attributed to ultrafast dynamics on the πσ* type state (3s a1 ← π 1a2), is demonstrated to be caused by the existence of pump + probe populated states, along the ionization process. The influence of these resonances in pump-prone ionization experiments, when multi-photon probes are used, and the significance of a proper zero-time reference, is discussed. The possibility of preparing the πσ* state by direct excitation is investigated by collecting 1 + 1 photoelectron spectra, at excitation wavelengths ranging from 255 to 219 nm. No conclusive evidences of ionization through this state are found.

An extensive laser spectroscopic, structural and computational investigation on the neurotransmitter analogue p -methoxyphenethylamine (MPEA) chromophore weakly bound to one molecule of water, (MPEA(H 2 O) 1 ) is reported. The complex was prepared by supersonic expansion of a gas mixture of seeded MPEA and water molecules in rare gas He. Two well-characterised experimental isomers have been observed, with geometries resulting from large contributions of the ordinary hydrogen bond and other intermolecular forces. Four key properties of the complex and related species are addressed in this paper: the characterisation of the isolated isomers observed spectra, the measurements of the binding energies of the ground, first electronic and ground ion states of the complex, the identification of each isomer spectrum with the computed geometries and the relationship of the complex stable isomers with the precursor conformers. A number of mass resolved laser spectroscopies have been used in order to get a complete set of experimental results, that complemented with ab initio density functional computations at four basis set, finally permitted us to settle and assign the mentioned properties of the two observed MPEA(H 2 O) 1 isomers.

Weakly bound complexes of phenol (Ph) and fluoromethane (CH3F) formed in a supersonic expansion have been identified by one- and two-color mass-resolved and hole burning spectroscopies. Only one isomer has been observed for the 1:1 complex. Threshold fragmentation has been employed to determine the binding energies of the complex in its ground, S0, and first electronic, S1, states, as well as in the ion ground state, I0, yielding the following results: D0(S0)=1540±50 cm−1, D0(S1)=1713±50 cm−1, and D0(I0)=3932±50 cm−1, respectively. In a complementary study, calculations on the complex geometries and binding energies were conducted at the B3LYP/6-31+G* and the MP2/6-31+G* levels. It has been shown that the binding energies computed at the MP2/6-31+G* level are in excellent agreement with the experimental values, whilst those calculated at the B3LYP/6-31+G* level underestimate them by nearly 30%, probably due to the poor description of the dispersion forces.

Binding or dissociation energies of the ground state, S0, the first electronic excited state, S1, and the ion ground state, I0, of the p-methoxyphenetylamine(H2O)1-4 complexes, referred to henceforth as either MPEA(H2O)1-4 or by their stoichiometric ratios 1:1−4, have been analyzed by threshold ion fragmentation. MPEA(H2O)1-4 complexes were prepared by the supersonic expansion of premixed samples containing appropriate amounts of MPEA and water molecules into carrier gas He. A number of isomers, with characteristic transition energies, have been identified: two for MPEA(H2O)1 at 35 676 and 35 689 cm-1, one for MPEA(H2O)2 at 35 687, one for MPEA(H2O)3 at 35 571 and two for MPEA(H2O)4 at 35 419 and 35 422 cm-1 respectively. The ionization energy and fragmentation thresholds, the latter defined as the onset energy of the process MPEA(H2O)n* + hν→ MPEA(H2O)n-1+ + H2O, have been determined, and from them the dissociation energies for the set of MPEA(H2O)1-4 isomers in their ground state, first electronic exci...

Weakly bound hydrogen bonded ethyl-p-aminobenzoate/water complexes, referred to henceforth both as EAB/(H2O)n (n=1–4) or by their stoichiometry 1:n, have been investigated with a combined approach of mass and light detector laser spectroscopic techniques and ab initio calculations. The experimental studies follow explorations with laser induced fluorescence (LIF), and include one-color resonant enhanced multiphoton ionization (REMPI), two-color REMPI (R2PI), pressure dependent R2PI and hole burning (HB) spectroscopies. Calculations were conducted at the B3LYP/6-31+G* level and for the 1:1 complex led to the existence of six stable isomers, identified as the experimental origin bands at +4, +6, +13, +89, +96, and +108 cm−1 above the bare EAB 000 transition. It has been shown that three of these bands originate in the EAB trans conformer, while the other three derive from the EAB gauche conformer. None of the experimental methods used lead us to observe the EAB(H2O)2 complex spectrum and the inspection of t...

A combined theoretical and experimental study of ethyl- p -aminobenzoate (EAB) molecule to substantiate the number of conformers, identify their electronic 0 0 0 transitions, vibrational bands, structures and ionisation energies is reported. The experimental study is mainly based on pump–probe laser techniques on the sample molecule prepared in a supersonic expansion beam and includes one-colour and two-colour resonance enhanced multiphoton ionisation (REMPI, R2PI) hole burning and dispersed emission spectroscopies. The spectra are rationalised with the help of density functional theory (DFT) computations at the B3LYP/6-31+G* level. EAB R2PI spectrum is reported for the first time and the trans and gauche conformers ionisation energy thresholds have been measured to be 7.828 and 7.826 eV, respectively. The small energy difference of the trans and gauche 0 0 0 transitions is suggested to be originated in the different contribution of the ethyl group orbitals to the conformer highest and lowest occupied molecular orbital states. Ground and first electronic excited states vibrational spectra of both conformers have been assigned with the help of the computed DFT vibrational wave numbers. The most intense bands of the vibrational spectra are identified as belonging to ring vibrations: 10a, 17b, 1+skeletal vibration, 5, 17a, 18b among others. Most vibrational modes in both conformers appear at close wave numbers and only the low energy modes, in the region below 400 cm −1 , should be regarded as the characteristic fingerprint of each conformer. No long vibrational progressions have been observed.

A combined wide range of laser spectroscopic techniques and computational quantum chemistry are used to investigate conformer landscapes of large substituted aromatic molecules. The spectroscopic techniques include laser-induced fluorescence (LIF), high-resolution LIF, resonance-enhanced multiphoton ionization (REMPI) with mass detection, two-color resonance ionization with mass detection (R2PI), laser dispersed emission (DE), and ion-dip hole burning (HB). These techniques are balanced with extensive ab initio DFT calculations at the B3LYP/6-31+G* and B3LYP/6-311+G* levels. These methods have been applied to investigate the nine possible conformations of the p−methoxyphenethylamine (MPEA) neurotransmitter molecule. Even when all the spectroscopic techniques play important roles, two color ionization energy (IE) threshold determinations have proven to be especially useful in the study. The gauche and anti conformers exhibit different ionization energy values, and even the amino hydrogen orientation influe...

Methyl-p-aminobenzoate(H2O)1 complex, henceforth MAB(H2O)1, prepared by pulsed supersonic expansion, has been examined by a broad range of laser based spectroscopic, mass and isomer selective techniques and density functional theory (DFT) calculations, in order to identify its isomer structures, ionization energies, and vibrational frequencies. The experimental techniques used include laser induced fluorescence (LIF), mass resolved excitation spectroscopy (MRES) either with one (REMPI) or two laser colors (R2PI), laser excited dispersed emission (DE), high resolution MRES, pressure controlled R2PI, hole burning (HB) spectroscopy, and photoion fragmentation threshold (PIFT). Experimental results have been interpreted, rationalized and extended with density functional theory (DFT) computations at the B3LYP/6-31G and B3LYP/6-31+G* levels. Although bare MAB molecule have four possible solvation sites, prone to yielding hydrogen bonds with the water molecule, LIF, R2PI, and HB spectroscopy of MAB(H2O)1 only pi...

Laser induced fluorescence, dispersed emission and two-colour ionisation spectroscopy (including the ionisation energy threshold) are suggested as an appropriate set of experimental methods for drawing the ground and excited state vibrational spectra of large organic molecules in presence of solvated molecules and dimers. In this Letter, they have been applied to obtain the vibrational spectrum of methyl- p -aminobenzoate (MAB). Parallel ground state ab initio calculations have enabled the geometry to be determined and the vibrational modes to be accurately assigned. The comparison of the ground and the first electronic excited state vibrational band wavenumbers shows an excellent agreement except for the excited state bands observed at 52.2, 565.6 and 579.7 cm −1 .

The ultrafast dynamics of the imidazole chromophore has been tracked after electronic excitation in the 250-217 nm energy region, by time delayed ionization with 800 nm laser pulses. The time-dependent signals collected at the imidazole(+) mass channel show the signature of femtosecond dynamics, originating on the πσ*- and ππ*-type states located in the explored energy region. The fitting of the transients, which due to the appearance of nonresonant coherent adiabatic excitation requires a quantum treatment based in the Bloch equations, yields two lifetimes of 18 ± 4 and 19 ± 4 fs. The first is associated with the πσ* ← ππ* internal conversion, while the second reflects the loss of ionization cross-section as the system evolves along the dissociative πσ* surface. This study provides a comprehensive picture of the photophysics of the molecule that agrees with previous experimental and theoretical findings.