Is it possible to perform an accurate study of the dynamic processes occurring in a chemical system, without a previous sound knowledge of its structure?

This was the question I placed at the beginning of my Ph.D thesis, that can summarize the scientific activity I’ve carried out till now, especially in the first years of my research activity.

M. Sc. thesis

During my University career, I’ve developed a strong interest in Reaction Dynamics and in the experimental possibility to real time follow the temporal evolution of a chemical system. For that I attended the courses “Chemical kinetics and Reaction Dynamics” by Prof. E. M. Castellucci and “Laboratory of Physical Chemistry IV” by Dr. M. Becucci, the last regarding advanced spectroscopic technique. Then I carried on the research work for my M.Sc. degree in Chemistry at the European Laboratory for Non-linear Spectroscopy (LENS), under the supervision of prof. Castellucci and dr. Becucci.

My research work based on the confidence of the necessity of an accurate structural analysis, before trying to explain the dynamics induced, for example, by an electronic excitation.

Attention to this topic was driven by my initial research work.

My M.Sc. Thesis (“Studio delle proprieta’ di complessi di Van der Waals per mezzo di spettroscopia di fotoionizzazione” – “A study on properties of Van der Waals complexes by means of photoionization spectroscopy”) has to be located exactly in this framework, dealing with the building and characterization of a Resonance Enhanced MultiPhoton Ionization – Time Of Flight (REMPI-TOF) spectrometer and the setting up of a sound strategy to resolve the structure of isolated molecules and weakly bonded clusters in the gas phase (see publications A.27 and A.26). This stratetegy is based on both experiments (REMPI and High Resolution Laser Induced Fluorescence, HR-LIF) and calculations (Molecular Mechanics, MM, and Quantum Mechanics, QM, methods). During the thesis work, I had the opportunity of collaborating with Prof. Wolfgang Demtroeder (University of Kaiserslautern, Germany).

Structural studies were performed combining experimental results (by means of experiments of vibrationally resolved REMPI and rotationally resolved Laser Induced Fluorescence) and theoretical data obtained from Molecular Mechanics, ab initio and Density Functional Theory calculations.

Doctorate

In the following years, attending the European Doctorate School on Atomic and Molecular Spectroscopy organized by LENS (again under the supervision of Prof. Castellucci), I worked to validate the efficiency of this approach for the study of weakly bonded systems, and to improve some experimental aspects, for example the REMPI signal detection (see publication A.24). Attention has been dedicated to the effect of electronic excitation on different systems (see publications A.23-A.20).

Among the complexes studied, in some cases they in essence maintain the same structure in going from the ground state, S₀, to the first excited state, S₁ (see the papers on anisole-H₂O and anisole-NH₃ complexes). In some other cases, vibrational predissociation occurs, like in some complexes studied by LENS group before my arrival. In other cases electronic excitation changes drastically the intermolecular forces, as demonstrated for aniline complexes with water and methanol. From these studies, and from attending international Congresses, Schools and Workshops, I found new impulse for my interest in Reaction Dynamics.

REMPI experiments provide basic information on the nature of the electronic excited states and their vibrational properties. These data are usually able to suggest the general aspects of the change of intermolecular interaction with electronic excitation. But the initial experimental resources available in the Molecular Beam Laboratory at LENS did not allow the study of dynamical processes. On one hand it was not possible to follow directly the time evolution of fast processes. On the other hand I was interested in the characterization of reaction products eventually generated by the laser excitation of the molecular systems. For that, I spent some months at the Universidad Complutense de Madrid (Madrid, Spain) in the group of Prof. F. J. Aoiz, working with Prof. L. Banares on the velocity mapping experiment they have just built in their lab, in order to take confidence with this technique.

Come back to LENS to finish my Doctorate course, I was involved in the construction and characterization of an apparatus for the detection of charged particles with imaging techniques, coupled with a nanosecond laser system. This kind of experiments, even in the ns time regime, provides more informations on the dynamical processes occurring in the system: for example, studying a photodissociation reaction, it is possible to have the spatial distribution of the produced photofragments.

UCSD Visiting Scientist and LENS post-doc

Once discussed my Ph.D. thesis on “Intermolecular interactions and reaction dynamics in the gas phase”, I went to San Diego, in the framework of a Transfer Of Knowledge (TOK) project, under a collaboration contract on “Dynamics and energetics of transient species in the gas phase: experimental methods”. There, I had the opportunity to work with Prof. Robert E. Continetti and his group, being involved in electron photodetachment experiment on anionic clusters of Iodine and small aromatic molecules, using a photoions/photoelectron coincidence apparatus. Results from this collaboration are presented in publication A.18.

As scheduled in the TOK program, coming back from San Diego I worked again at LENS, where I had (November 2007 – April 2010) a post-doctoral fellowship (assegno di ricerca) on “Chemical Dynamics in isolated systems: experimental studies”. In this framework, I have continued studies on bimolecular complexes in the gas phase, especially on dimers of small aromatic molecules (publications A.19 and A.17), on photodissociation reactions studied in a ns time regime (publication A.16) and on photoionization of small molecules studied by photoelectron imaging (publication A.13). In parallel I worked to couple the LENS imaging apparatus with a femtosecond laser source, with the aim to start a new research line at LENS, i.e. the time-resolved study of reaction dynamics in the gas phase. In this framework, I’ve become interested to the field of coherent control of reaction dynamics: for that I’ve attended the EPSRC Summer School on “Coherent Control of Molecules” held in London in April 2009. I have also presented a project on this subject to the Italian Ministero dell’Istruzione, dell’Universita’ e della Ricerca in the framework of FIRB 2008, positively evaluated by the assigned international referee.

I have acquired both experimental and computational skills. From this last point of view, I’ve become confident with the software packages ORAC, for MM calculations performed in order to explore the ground state Potential Energy Surface of the complex systems I’ve studied, and GAUSSIAN 03, for QM calculations in both the ground state (ab initio and DFT methods, to obtain structural information with an accuracy compatible with the HR-LIF experimental data) and the excited states (TD-DFT methods, to study dissociation dynamics).

I also collaborated with researchers in completely different field, contributing in the experimental work thanks to the confidence I’ve acquired with laser systems. Publications A.25 and A.14 have to be considered in this framework.

LFP post-doc

At the beginning of 2010, I have decided to leave the LENS group in order to improve my international experience and to acquire a more sound knowledge on the time-resolved photoelectron spectroscopy: for that I’ve joined the Reaction Dynamics group at the Laboratoire Francis Perrin (CEA Saclay, France). Here I’ve been involved in a project whose aim was to explore the spectroscopy of photochromic molecules in the gas phase under different environments (free molecules or deposited on Argon cluster) and then conduct time-resolved photoelectron spectroscopy on the same samples; other aims of the same project were related to nanoparticles.

At the LFP, I’ve essentially worked on diarylethenes (publications B.1 and A.5). These molecules present a photochromic activity, and they are very promising for an application in optoelectronical devices. Their photochromism is due to the existence of two isomers, and the isomerization can be induced by light. Using ultrafast ionization techniques in the gas phase, I’ve been able to point out the presence of different relaxation pathways (conical intersection and vibronic coupling) from the excited state of one isomer to the ground state of the other. Moreover I recognized the presence in the sample of different conformers of the starting isomer. I also worked on other different molecules of the same class in order to understand the effect of substituents and geometrical constraints on the diarylethene frame. The studies on deposited molecules (on Ar_n clusters) shown a slowing effect on the dynamics, due to solvation. In order to study these molecules in more complex (and more “realistic”) media, I also worked at the equipment of the femtosecond experimental setup of the LFP’s Reaction Dynamics group with an aerosol source to put nanoparticles in the gas phase.

Then I collaborated with Dr. Stéphane Aloïse (University of Lille, France), Prof. Ingo Fisher (University of Würzburg, Germany) and Dr. Anna Szemik-Hojniak (University of Wroclaw, Poland) on the time-resolved photoelectron spectroscopy of different systems (SBPA, fluorenone, radicals, proton sponges…) (publications A.8 - A.10 and A.2). I was also involved in a project on the ionization dynamics of Ar_n clusters (publication A.1), with experiments at DESIRS beamline at SOLEIL synchrotron (France).

I continued to collaborate with my former LENS group on the energetics and photodissociation dynamics of pyrrol and its derivatives, performing experiments at the GasPhase PhotoEmission beamline at ELETTRA synchrotron (Italy).

ATER position at Paris-Sud University

In September 2012 I moved to the Paris-Sud University for a temporary teaching position. I was involved in a project dealing with the characterization of the energetics and the structure of bichromophoric systems. I asked to work in the group of Dr. Anne Zehnacker at the ISMO, Institut des Sciences Moléculaires d’Orsay, aiming at acquiring expertise in double resonance experiments. I worked on the effect of local chirality on protonated dipeptides, experimentally investigated by InfraRed MultiPhoton Dissociation at CLIO, the Orsay FEL, and to a pioneering experiment based on the coupling of a UV laser with a Pauli trap, in order to study the photoinduced fragmentation of ionic species in the gas phase (publications A.7 and A.3). Due to the interest on chiral recognition topic, I spent a week in Berlin (in Prof. Dr. Otto Dopfer lab), investigating indanol by tandem spectroscopy (publication A.4).

UCLM post-doc

In September 2013 I moved to Spain to join the FemtoChemistry and Microscopy group (animated by Prof. Abderrazak Douhal) at the Universidad de Castilla-La Mancha. I was interested to improve my knowledge and expertise in state- and time-resolved spectroscopic techniques in the condensed phase, with a particular attention to applied research, especially in the field of solar energy harvesting and conversion (publication A.6). I also elaborated and submitted a MarieCurie IEF (Intra-European Fellowship) project, focused on the study of Dye-Sensitized Solar Cell by means of femtosecond resolved up-conversion technique and Single Molecule Spectroscopy.