Search results for "intersection"
showing 10 items of 213 documents
Quantum Chemistry of Excited States in Polyhedral Boranes
2015
In this Chapter we describe the electronic structure of ground states and excited states of the two isomers of octadecaborane (22), anti- and syn-B18H22, and the new derivative of anti-B18H22, the polyhedral substituted borane 4,4′-(HS)2-anti-B18H20. A theoretical interpretation is given on the fluorescence of the anti-B18H22 isomer, and the non-radiative decay of the syn-B18H22 isomer, an unsolved problem since 1962. For the new derivative of anti-B18H22, substitution of hydrogen atoms in positions 4 and 4′ by SH groups allows the tuning of the photophysical properties in 4,4′-(HS)2-anti-B18H20, facilitating intersystem crossing from the excited singlet state to the triplet state.
Theoretical CASPT2 study of the excited state double proton transfer reaction in the 7-azaindole dimer
2006
Accurate CASPT2 calculations on the excited state double proton transfer reaction in the 7-azaindole dimer have been performed on different symmetric and asymmetric pathways along the protons interchange. The presence of a conical intersection connecting the initially photoinduced singlet excited state with a charge transfer state leading both to asymmetric ionic and neutral structures promotes a step-wise mechanism, probably taking place through the ionic intermediate. The concerted path is computed slightly higher in energy in the gas phase.
Co-riding With My eBike to Get Green Lights
2019
Researchers are increasingly exploring interactive technology supporting human-system partnership in an exertion context, such as cycling. So far, most investigations have supported the rider cognitively, by the system "sensing and presenting" information to assist the rider to make informed decisions. In contrast, we propose systems that promote user-system co-operation, by "sensing and acting" on information to assist the rider, not only "cognitively" but also "physically", with the aim of facilitating user-system co-operation in an exertion context. Our prototype, "Ari", is a novel augmented eBike designed to facilitate user-system co-operation, where the information that each party can …
Los beneficios del mar: negocios e inversiones económicas de la oficialidad naval en el siglo XVIII
2019
Throughout the eighteenth century, the Spanish navy was extensively reformed and enhanced as a consequence of the new model of Monarchy that the Bourbons introduced. Among the measures adopted, it is remarkable the erection of the naval officers corps according to the needs and obligations that maritime war had in this century. This group becomes the paradigm of the new professionalization and new training approach, and its members had great relevance due to its great mobility around the empire and the power of the naval institution. This means that a part of the naval officers were placed in privileged positions and at the intersection of diverse political, social and economic networks. Th…
The role of the low-lying dark np* states in the photophysics of pyrazine: a quantum dynamics study
2014
The excited state dynamics of pyrazine has attracted considerable attention in the last three decades. It has long been recognized that after UV excitation, the dynamics of the molecule is impacted by strong non-adiabatic effects due to the existence of a conical intersection between the B2u(ππ*) and B3u(nπ*) electronic states. However, a recent study based on trajectory surface hopping dynamics simulations suggested the participation of the Au(nπ*) and B2g(nπ*) low-lying dark electronic states in the ultrafast radiationless decay of the molecule after excitation to the B2u(ππ*) state. The purpose of this work was to pursue the investigation of the role of the Au(nπ*) and B2g(nπ*) states in…
Quantum chemical study on the population of the lowest triplet state of psoralen
2007
Abstract The efficient population of the low-lying triplet ππ * state of psoralen is studied with the quantum chemical CASPT2 method. Minima, singlet–triplet crossings, conical intersections, and reaction paths on the low-lying singlet and triplet states hypersurfaces of the system have been computed together with electronic energy gaps and spin–orbit coupling terms. A mechanism is proposed, favorable in the gas phase, for efficient deactivation of the initially populated singlet excited ππ * state, starting with an intersystem crossing with an n π * triplet state and evolving via a conical intersection toward the final lowest-lying ππ * triplet state, protagonist of the reactivity of psora…
Pyrene, a Test Case for Deep-Ultraviolet Molecular Photophysics
2019
We determined the complete relaxation dynamics of pyrene in ethanol from the second bright state, employing experimental and theoretical broadband heterodyne detected transient grating and two-dimensional photon echo (2DPE) spectroscopy, using pulses with duration of 6 fs and covering a spectral range spanning from 250 to 300 nm. Multiple lifetimes are assigned to conical intersections through a cascade of electronic states, eventually leading to a rapid population of the lowest long-living excited state and subsequent slow vibrational cooling. The lineshapes in the 2DPE spectra indicate that the efficiency of the population transfer depends on the kinetic energy deposited into modes requir…
Adenine and 2-aminopurine: Paradigms of modern theoretical photochemistry
2006
Distinct photophysical behavior of nucleobase adenine and its constitutional isomer, 2-aminopurine, has been studied by using quantum chemical methods, in particular an accurate ab initio multiconfigurational second-order perturbation theory. After light irradiation, the efficient, ultrafast energy dissipation observed for nonfluorescent 9H-adenine is explained here by the nonradiative internal conversion process taking place along a barrierless reaction path from the initially populated 1 (ππ* L a ) excited state toward a low-lying conical intersection (CI) connected with the ground state. In contrast, the strong fluorescence recorded for 2-aminopurine at 4.0 eV with large decay lifetime …
Críticas al derecho y el sujeto “mujeres” y propuestas desde la jurisprudencia feminista | Criticism to the Law and the Subject “Women” and Proposals…
2014
Resumen: Las feministas tradicionalmente han criticado el derecho como un instrumento de opresión de las mujeres. Se ha duda sobre la capacidad del derecho de transformar la realidad y ser capaz de traducir legalmente las demandas políticas de las mujeres, mejorando sus vidas. Además, los últimos movimientos feministas han sido muy escépticos con la viabilidad de la categoría “mujeres” como sujeto del derecho. Este artículo analiza estas dudas y críticas recuperando algunas de las propuestas hechas por las juristas feministas para crear nuevas categorías jurídicas que incluyan las demandas y necesidades de las mujeres y desplacen la importancia del sujeto. Abstract: Feminists have traditi…
Il concetto di intersezionalità fra teorie femministe e sociologia
2019
Il saggio offre una panoramica del concetto di intersezionalità, delle sue articolazioni, delle criticità teoriche e metodologiche che lo attraversano, concludendo con un’analisi delle principali interazioni con le categorie sociologiche. The essay offers an overview of the concept of intersectionality, its articulations, the theoretical and methodological criticalities that cross it, concluding with an analysis of the main interactions with sociological categories.