9 research outputs found
Ultrafast dissociation dynamics of 2-Ethylpyrrole
To explore the effects of ring substitution on dissociation dynamics, the primary photochemistry of 2-ethylpyrrole has been explored using ultrafast ion imaging techniques. Photoexcitation to the S1 state, a ÏÏ* state, in the range of 238 to 265 nm results in cleavage of the NâH bond with an H-atom appearance lifetime of ca. 70 fs. The insensitivity of this lifetime to photon energy, combined with a small kinetic isotope effect, suggests that tunneling does not play a major role in NâH bond cleavage. Total kinetic energy release spectra reveal modest vibrational excitation in the radical counter-fragment, increasing with photon energy. At wavelengths †248 nm a second, low kinetic energy H-atom loss mechanism becomes available with an appearance lifetime of approximately 1.5 ps and possibly due to the population of higher lying 1ÏÏ* states
Bottom-up excited state dynamics of two cinnamate-based sunscreen filter molecules
Methyl-E-4-methoxycinnamate (E-MMC) is a model chromophore of the commonly used commercial sunscreen agent, 2- ethylhexyl-E-4-methoxycinnamate (E-EHMC). In an effort to garner a molecular-level understanding of the photoprotection mechanisms in operation with E-EHMC, we have used time-resolved pump-probe spectroscopy to explore E-MMCâs and E-EHMCâs excited state dynamics upon UV-B photoexcitation to the S1 (11ÏÏ*) state in both the gas- and solution-phase. In the gas-phase, our studies suggest that the excited state dynamics are driven by non-radiative decay from the 11ÏÏ* to the S3 (11nÏ*) state, followed by de-excitation from the 11nÏ* to the ground electronic state (S0). Using both a non-polar-aprotic solvent, cyclohexane, and a polar-protic solvent, methanol, we investigated E-MMC and EEHMCâs photochemistry in a more realistic, âcloser-to-shelfâ environment. A stark change to the excited state dynamics in the gas-phase is observed in the solution-phase suggesting that the dynamics are now driven by efficient E/Z isomerisation from the initially photoexcited 11ÏÏ*state to S0
Infrared spectroscopy of thin films of functional oxides deposited on silicon : the ab initio contribution to modeling
Le PbZrâââTiâOâ (PZT) est une pĂ©rovskite mixte possĂ©dant de nombreuses propriĂ©tĂ©s, dont certaines sont dĂ©jĂ utilisĂ©es dans lâindustrie, ce qui en fait un matĂ©riau encore trĂšs Ă©tudiĂ© Ă lâheure actuelle, malgrĂ© la toxicitĂ© du plomb et de ses oxydes. Au cours de cette thĂšse, nous nous sommes intĂ©ressĂ©s Ă la spectroscopie dâabsorption IR de ce composĂ©, tant au niveau expĂ©rimental que thĂ©orique. Nous avons donc rĂ©alisĂ© des modĂ©lisations, via le code de calcul CRYSTAL basĂ© sur les mĂ©thodes de Combinaison LinĂ©aire dâOrbitales Atomiques et de la ThĂ©orie de la Fonctionnelle de la DensitĂ© (LCAO-DFT) pĂ©riodique, afin dâaider Ă lâinterprĂ©tation des spectres expĂ©rimentaux rĂ©alisĂ©s sur la ligne AILES du synchrotron SOLEIL. Dans ce but, nous avons commencĂ© par modĂ©liser les composĂ©s de base du PZT : le PbTiOâ (PT) et le PbZrOâ (PZ). Nos rĂ©sultats reproduisant trĂšs bien les donnĂ©es de la littĂ©rature sur ces deux composĂ©s, nous avons pu faire une analyse fine de leur spectre dâabsorption IR. Dâautre part, leur modĂ©lisation nous a permis de dĂ©terminer des paramĂštres de calcul transfĂ©rables (base et fonctionnelle notamment) et de les appliquer sur le PZT en utilisant la mĂ©thode de la supermaille, couplĂ©e Ă une analyse statistique. Les rĂ©sultats obtenus sont prometteurs pour lâinterprĂ©tation, car tout Ă fait comparables aux spectres expĂ©rimentaux. Afin de nous rapprocher au mieux du cristal rĂ©el de PT, nous nous sommes intĂ©ressĂ©s Ă la modĂ©lisation de couches ultraminces et de lacunes dâoxygĂšne, dans le but de voir leur effet sur le spectre dâabsorption IR du PT.PbZrâââTiâOâ (PZT) is a complex perovskite that has many properties, some of which are already used industrially. Thus, in spite of the toxicity of lead and its oxides, this material is still under extensive investigation. In this thesis, we are interested of both experimental and theoretical IR absorption spectroscopy of this compound. To do so, we used the CRYSTAL code, based on the Linear Combination of Atomic Orbitals method and periodic Density Functional Theory (LCAO-DFT) in order to facilitate the interpretation of experimental spectra, recorded on the AILES beamline of synchrotron SOLEIL. In this goal, we first studied the two building blocks of PZT: PbTiOâ (PT) and PbZrOâ (PZ). Our results are in very good agreement with what has already been done in the literature. We, thus, could carry out a precise interpretation of their absorbance spectra. Moreover, transferable parameters (in particular the basis set and the functional) have been determined and used to study PZT. The supercell method, coupled with a statistical analysis, provided promising results, comparable with experimental data and, thus, helpful for their interpretation. In order to make a step towards the real PT crystal, we started the simulation of ultrathin films and oxygen vacancies to investigate their effects on the IR absorption spectrum
Etude par spectroscopie infrarouge de films minces dâoxydes fonctionnels intĂ©grĂ©s sur silicium : apport des modĂ©lisations ab initio
PbZrâââTiâOâ (PZT) is a complex perovskite that has many properties, some of which are already used industrially. Thus, in spite of the toxicity of lead and its oxides, this material is still under extensive investigation. In this thesis, we are interested of both experimental and theoretical IR absorption spectroscopy of this compound. To do so, we used the CRYSTAL code, based on the Linear Combination of Atomic Orbitals method and periodic Density Functional Theory (LCAO-DFT) in order to facilitate the interpretation of experimental spectra, recorded on the AILES beamline of synchrotron SOLEIL. In this goal, we first studied the two building blocks of PZT: PbTiOâ (PT) and PbZrOâ (PZ). Our results are in very good agreement with what has already been done in the literature. We, thus, could carry out a precise interpretation of their absorbance spectra. Moreover, transferable parameters (in particular the basis set and the functional) have been determined and used to study PZT. The supercell method, coupled with a statistical analysis, provided promising results, comparable with experimental data and, thus, helpful for their interpretation. In order to make a step towards the real PT crystal, we started the simulation of ultrathin films and oxygen vacancies to investigate their effects on the IR absorption spectrum.Le PbZrâââTiâOâ (PZT) est une pĂ©rovskite mixte possĂ©dant de nombreuses propriĂ©tĂ©s, dont certaines sont dĂ©jĂ utilisĂ©es dans lâindustrie, ce qui en fait un matĂ©riau encore trĂšs Ă©tudiĂ© Ă lâheure actuelle, malgrĂ© la toxicitĂ© du plomb et de ses oxydes. Au cours de cette thĂšse, nous nous sommes intĂ©ressĂ©s Ă la spectroscopie dâabsorption IR de ce composĂ©, tant au niveau expĂ©rimental que thĂ©orique. Nous avons donc rĂ©alisĂ© des modĂ©lisations, via le code de calcul CRYSTAL basĂ© sur les mĂ©thodes de Combinaison LinĂ©aire dâOrbitales Atomiques et de la ThĂ©orie de la Fonctionnelle de la DensitĂ© (LCAO-DFT) pĂ©riodique, afin dâaider Ă lâinterprĂ©tation des spectres expĂ©rimentaux rĂ©alisĂ©s sur la ligne AILES du synchrotron SOLEIL. Dans ce but, nous avons commencĂ© par modĂ©liser les composĂ©s de base du PZT : le PbTiOâ (PT) et le PbZrOâ (PZ). Nos rĂ©sultats reproduisant trĂšs bien les donnĂ©es de la littĂ©rature sur ces deux composĂ©s, nous avons pu faire une analyse fine de leur spectre dâabsorption IR. Dâautre part, leur modĂ©lisation nous a permis de dĂ©terminer des paramĂštres de calcul transfĂ©rables (base et fonctionnelle notamment) et de les appliquer sur le PZT en utilisant la mĂ©thode de la supermaille, couplĂ©e Ă une analyse statistique. Les rĂ©sultats obtenus sont prometteurs pour lâinterprĂ©tation, car tout Ă fait comparables aux spectres expĂ©rimentaux. Afin de nous rapprocher au mieux du cristal rĂ©el de PT, nous nous sommes intĂ©ressĂ©s Ă la modĂ©lisation de couches ultraminces et de lacunes dâoxygĂšne, dans le but de voir leur effet sur le spectre dâabsorption IR du PT
Confinement Effects on the Nuclear Spin Isomer Conversion of H <sub>2</sub> O
International audienceThe mechanism for interconversion between the nuclear spin isomers (NSI) of H2O remains shrouded in uncertainties. The temperature dependence displayed by NSI interconversion rates for H2O isolated in an argon matrix provides evidence that confinement effects are responsible for the dramatic increase in their kinetics with respect to the gas phase, providing new pathways for o-H2Oâp-H2O conversion in endohedral compounds. This reveals intramolecular aspects of the interconversion mechanism which may improve methodologies for the separation and storage of NSI en route to applications ranging from magnetic resonance spectroscopy and imaging to interpretations of spin temperatures in the interstellar medium
FDDYNAM16 Towards elucidating the photochemistry of the sunscreen filter ethyl ferulate using time-resolved gas-phase spectroscopy
Ultrafast time-resolved ion yield (TR-IY) and velocity map imaging spectroscopies are employed to reveal the relaxation dynamics after photoexcitation in ethyl 4-hydroxy-3-methoxycinnamate (ethyl ferulate, EF), an active ingredient in commercially available sunscreens. In keeping with a bottom-up strategy, the building blocks of EF, 2-methoxy-4-vinylphenol (MVP) and 4-hydroxy-3-methoxycinnamyl alcohol (coniferyl alcohol, ConA), were also studied to assist in our understanding of the dynamics of EF as we build up in molecular complexity. In contrast to the excited state dynamics of MVP and ConA, which are described by a single time constant (>900 ps), the dynamics of EF are described by three time constants (15 ± 4 ps, 148 ± 47 ps, and >900 ps). A mechanism is proposed involving internal conversion (IC) between the initially excited S1(11ÏÏ*) and S2(11nÏ*) states followed by intramolecular vibrational redistribution (IVR) on both states, in competition with intersystem crossing onto neighbouring triplet states (15 ± 4 ps). IVR and IC within the triplet manifold then ensues (148 ± 47 ps) to populate a low-lying triplet state (>900 ps). Importantly, the fluorescence spectrum of EF at the S1 origin, along with the associated lifetime (6.9 ± 0.1 ns), suggests that population is trapped, during initial IVR, on the S1(11ÏÏ*) state. This serves to demonstrate the complex, competing dynamics in this sunscreen filter molecule