Search results for "conical"

Toward an Understanding of Ultrafast Electron Transfer in Photosynthesis

2008

The mechanism of electron transfer (ET) from reduced pheophytin (Pheo−) to the primary stable photosynthetic acceptor, a quinone (Q) molecule, is addressed by using high-level ab initio computations and realistic molecular models. The results reveal that the ET process involving the (Pheo−+Q) and (Pheo+Q−) oxidation states can be seen essentially as an ultrafast radiationless transition between the two hypersurfaces taking place via conical intersections (CIs) and is favoured when the topology of the interacting moieties makes possible some overlap between the lowest occupied molecular orbitals (LUMO) of the two systems. Thus, it is anticipated that large scale motions, which are difficult …

2014

There have been a number of recent experimental investigations of the nonadiabatic relaxation dynamics of aniline following excitation to the first three singlet excited states, 1(1)ππ*, 1(1)π3s/πσ* and 2(1)ππ*. Motivated by differences between the interpretations of experimental observations, we have employed CASSCF and XMCQDPT2 calculations to explore the potential energy landscape and relaxation pathways of photoexcited aniline. We find a new prefulvene-like MECI connecting the 1(1)ππ* state with the GS in which the carbon-atom carrying the amino group is distorted out-of-plane. This suggests that excitation above the 1(1)π3s/πσ* vertical excitation energy could be followed by electronic…

Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands

2018

We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry atQband (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique atUband (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σlevel betweenUandQbands. With the benefit of quasi-simultaneousUandQband observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three d…

Jet stability and the generation of superluminal and stationary components

2001

We present a numerical simulation of the response of an expanding relativistic jet to the ejection of a superluminal component. The simulation has been performed with a relativistic time-dependent hydrodynamical code from which simulated radio maps are computed by integrating the transfer equations for synchrotron radiation. The interaction of the superluminal component with the underlying jet results in the formation of multiple conical shocks behind the main perturbation. These trailing components can be easily distinguished because they appear to be released from the primary superluminal component, instead of being ejected from the core. Their oblique nature should also result in distinc…

Can coupled-cluster theory treat conical intersections?

2007

Conical intersections between electronic states are of great importance for the understanding of radiationless ultrafast relaxation processes. In particular, accidental degeneracies of hypersurfaces, i.e., between states of the same symmetry, become increasingly relevant for larger molecular systems. Coupled-cluster theory, including both single and multireference based schemes, offers a size-extensive description of the electronic wave function, but it sacrifices the Hermitian character of the theory. In this contribution, we examine the consequences of anti-Hermitian contributions to the coupling matrix element between near-degenerate states such as linear dependent eigenvectors and compl…

Focal squeeze in axicons

2005

The on-axis irradiance distribution of a truncated conical wavefront is evaluated in terms of the Fresnel number of the focusing geometry. In agreement with geometrical optics, a focal line of increasing intensity is generated for extremely high Fresnel numbers. Otherwise clear deviations may be observed for the position of the maximum irradiance along the optical axis. A remarkable focal squeeze appears and, for decreasing Fresnel numbers, this effect manifests stronger. An analytical formula is provided for the fast evaluation of the focal squeeze.

Similar chemical structures, dissimilar triplet quantum yields: a CASPT2 model rationalizing the trend of triplet quantum yields in nitroaromatic sys…

2019

The photophysics of nitroaromatics compounds stand out for being characterized by an ultrafast decay into the triplet manifold and by a significant value of the triplet quantum yield. The latter quantity can change dramatically from one system to another, as proven for the molecules 2- nitronaphthalene, 1-nitronaphthalene, and 2methyl-1nitronaphthale, whose triplet quantum yield have been previously measured to be 0.93 ± 0.15, 0.64 ± 0.12, and 0.33 ± 0.05, respectively (J. Phys. Chem. A 2013, 117, 14100). In the present contribution we rationalize the reported trend for the triplet quantum yield on the basis of the different ability that the excited S 1 state has in the three molecules to r…

(2+1)-dimensional Einstein-Kepler problem in the centre-of-mass frame

1999

We formulate and analyze the Hamiltonian dynamics of a pair of massive spinless point particles in (2+1)-dimensional Einstein gravity by anchoring the system to a conical infinity, isometric to the infinity generated by a single massive but possibly spinning particle. The reduced phase space \Gamma_{red} has dimension four and topology R^3 x S^1. \Gamma_{red} is analogous to the phase space of a Newtonian two-body system in the centre-of-mass frame, and we find on \Gamma_{red} a canonical chart that makes this analogue explicit and reduces to the Newtonian chart in the appropriate limit. Prospects for quantization are commented on.

Emission and null coordinates: geometrical properties and physical construction

2011

A Relativistic Positioning System is defined by four clocks (emitters) broadcasting their proper time. Then, every event reached by the signals is naturally labeled by these four times which are the emission coordinates of this event. The coordinate hypersurfaces of the emission coordinates are the future light cones based on the emitter trajectories. For this reason the emission coordinates have been also named null coordinates or light coordinates. Nevertheless, other coordinate systems used in different relativistic contexts have the own right to be named null or light coordinates. Here we analyze when one can say that a coordinate is a null coordinate and when one can say that a coordin…

Transition From Ideal To Viscous Mach Cones In A Partonic Transport Model

2013

Using a partonic transport model we investigate the evolution of conical structures in ultrarelativistic matter. Using two different source terms and varying the transport properties of the matter we study the formation of Mach Cones. Furthermore, in an additional study we extract the two-particle correlations from the numerical calculations and compare them to an analytical approximation. The influence of the viscosity to the shape of Mach Cones and the corresponding two-particle correlations is studied by adjusting the cross section of the medium. peerReviewed