Investigation of charge migration/transfer in radical cations using Ehrenfest method with fully quantum nuclear motion

The main focus of this thesis is to investigate the effect of charge migration on molecular dynamics. Upon the creation of a superposition of cationic states by a short ionizing pulse in an attosecond pump-probe experiment, the electronic wavefunction is in a non-stationary state and the initial dynamics are purely electronic, driven by Charge Migration (CM) before the onset of any nuclear motions. The CM can be simulated using a frozen nuclear framework but its importance on long-term dynamics and competition with vibrationally mediated charge motion (i.e. Charge Transfer (CT)) remains unknown. Unravelling the mechanism behind CM and its importance on electron and nuclear coherence can help in designing an initial superposition of electronic states to steer nuclear motions toward a specific product. Further control of the photo-reactivity could be achieved with the use of probe/control laser pulses and open the door for more direct comparison with experimental results. In order to investigate the dynamics upon photoionization with an attosecond pump-pulse, the coupled electron-nuclear dynamics of the system is simulated using nonadiabatic quantum dynamics techniques within the sudden approximation. A single-set approach is adopted for the expansion of the nuclear wavefunction using a linear combination of Gaussian Wavepackets (GWP). The calculation is done using the Quantum-Ehrenfest method (QuEh) and the time-dependent Potential Energy Surfaces (PES) are evaluated with the Complete Active Space Configuration Interatcion (CAS-CI) method. The resulting dynamics are analyzed with adiabatic/diabatic state populations, Normal Mode (NM) displacements and bond lengths averaged over the nuclear wavepacket using Gross Gaussian populations (GGP). To reduce the cost of computation, the algorithm implemented in QUANTICS is parallelized with a Message Passing Interface (MPI). Further, the section of code which interacts with the database that contains previously calculated points on the PES is rewritten using the Structured Query Language (SQL) and the SQLite engine. For the purpose of unravelling the mechanism behind CM, the nonadiabatic dynamics of a model retinal Protonated Schiff Base (rPSB) and benzene are investigated by defining the initial electronic wavefunction in a systematic way. As demonstrated by the results on rPSB, the relaxation mechanism such as single and double bond length alternation and isomerization can controlled by varying the initial composition of electronic states. With the rich symmetry of benzene, the initial nuclear dynamics which are controlled by an initial gradient and electron dynamics can be analyzed using symmetry rules. The initial gradient is a combination of totally symmetric motion and non-symmetric components which correspond to the intra- (eigenstate) and inter-state (couplings) gradients, respectively. The electron dynamics and its associated nuclear motions can be examined by grouping together the localized holes where the CM occurs. With the initial gradient and CM, one can predict the initial nuclear relaxation and possibly control the photo-products formed by designing a specific superposition of electronic eigenstates. To explore the effect of laser pulses on dynamics, an implementation within the dipole approximation using the dipole-electric field dot product is done in the GAUSSIAN program. The dynamics in the presence of an infrared probe pulse is simulated on model systems such as allene and the ethylene cation. The pulse is able to induce change in the electron and nuclear dynamics of the system and some of its effect can be explained using irreducible representations and the alignment of the electric fields. The work presented in this thesis offers an insight into the photocontrol of molecules and opens the door for further investigation of charge-directed dynamics

Introduction to LCA, interests and opportunities for the rubber supply chain

Life Cycle Assessment (LCA) is a product-oriented method to assess the environmental impacts of a product while accounting for its whole life cycle, "from the cradle to the grave". It is standardised by international norms (ISO, 2006). It was first mostly used for eco-conception in industrial productions, but has been widely spread in the agricultural sector in the last twenty years. By its holistic nature, LCA is a unique method to assess several environmental impacts while avoiding pollution trade-offs between production stages or impact categories. The most renowned impact categories are climate change or energy use, but several other impact categories can also be assessed such as eutrophication or human toxicity. With the growing awareness of the risks associated with climate change and the need to protect the environment, the design of eco-friendly production modes has become critical. Throughout the world, initiatives from both the private and public sectors promote the development of sustainable supply chains including the development of communication tools using LCA indicators. In France, a law was recently promulgated (Grenelle 1, 2009) that makes the eco-labelling based on LCA compulsory for a wide range of products such as food and pet food, automobile, clothes, electronics etc. Application of LCA to agricultural products or bio-sourced materials is not straightforward due to the variability in agricultural production systems. This variability is particularly important in the Tropics, where both pedo-climatic and socio-cultural conditions greatly vary. To account for the influence of these conditions on the field emissions and the final impacts within LCA, methodological developments are being carried out by the scientific community. Researchers at CIRAD especially focus on how to better account for tropical specificities and perennial crops within LCA (Bessou et al., 2012). They work together with several partners in France (www.elsa-lca.org) and abroad, and CIRAD is notably member of the LCA AgriFood ASIA Network (http://lca-agrifood-asia.org). Undoubtedly, there is a good opportunity for the actors in the rubber supply chain to benefit from the researches at CIRAD and the dynamism of the LCA AgriFood ASIA Network. Environmental impacts of rubber products will necessarily need to be assessed in a short to medium term, for instance because of buyers requests, and LCA has become the most commonly used method in order to compare products. As a perennial crop, not used for food products, it is crucial to assess the assets and drawbacks of rubber production in order to define best management practices and supply chain strategies to limit environmental impacts. (Résumé d'auteur

A comprehensive model of the optical spectra of carbon nanotubes on substrate by polarized microscopy

Polarized optical microscopy and spectroscopy are progressively becoming key methods for the high-throughput characterization of individual carbon nanotubes (CNTs) and other one-dimensional nanostructures, on substrate and in devices. The optical response of CNTs on substrate in cross polarization experiments is usually limited by the polarization conservation of the optical elements in the experimental setup. We developed a theoretical model taking into account the depolarization by the setup and the optical response of the substrate. We show that proper modelization of the experimental data requires to take into account both non-coherent and coherent light depolarization by the optical elements. We also show how the nanotube signal can be decoupled from the complex reflection factor of the anti-reflection substrate which is commonly used to enhance the optical contrast. Finally, we describe an experimental protocol to extract the depolarization parameters and the complex nanotube susceptibility, and how it can improve the chirality assignment of individual carbon nanotubes in complex cases.Comment: 10 pages, 7 Figures, submitted to PRB. A supplementary information completes this pape