Search results for "excited states"
showing 10 items of 51 documents
Triplet 12B-12C-12N : Search for States with Halo
2020
Previously in [1] neutron halo was confirmed for the 2¯, 1.67 MeV and 1¯, 2.62 MeV states in 12B on base of Asymptotic Normalization Coefficients (ANC) method analysis of the obtained experimental data. An unexpected result was received for the unbound 3¯, 3.39 MeV state. Its halo radius was found to be increased and equal to ~5.9 fm. This result can be considered as an evidence of the halo-like structure in this 12B state. It should be noted that last neutron in this state has a non-zero orbital momentum (l = 2). So question arises about possible existence of states with halo in other members of the isobaric triplet 12B–12C–12N. We can expect the formation of a proton halo in the 2¯, 1.19 …
Toward the understanding of DNA fluorescence: The singlet excimer of cytosine
2006
By using the multiconfigurational second-order perturbation method CASPT2, including corrections for the basis set superposition error, the lowest-singlet excited state of the face-to-face π-stacked cytosine homodimer is revealed to be bound by about half an eV, being the source of an emissive feature consistent with the observed redshifted fluorescence. Gloria.Olaso@uv.es Daniel.Roca@uv.es Luis.Serrano@uv.es Manuela.Merchan@uv.es
Electronic structure of the ground and excited states of beta-carboline.
2008
Coupled-cluster calculations are used to compute the energy of conversion between the neutral and the zwitterionic forms of beta-carboline. The stability of the different species is discussed in terms of charge separation and aromatic character, which is related to magnetic criteria. By means of a linear response formalism the vertical excitation energies and oscillator strengths of the lowest singlet states of both structures as well as of the cationic species are determined. General agreement of the relative position and intensity of the different peaks with experimental data is achieved, but the overall spectra are slightly displaced because of solvent effects.
Electronic excited states of conjugated cyclic ketones and thioketones : A theoretical study
2002
Absorption spectra of a series of cyclic conjugated ketones and thioketones have been computed at the multiconfigurational second-order multistate perturbation level of theory, the CASSCF/MS-CASPT2 method. Excitation energies, transition dipole moments, oscillator strengths, and static dipole moments are reported and discussed for excited states with energies lower than ≈ 7–8 eV. The main bands of the spectra have been assigned and characterized in most cases for the first time. The spectroscopy of the different systems is compared in detail. Thioketones in particular have low-energy and intense ππ∗ transitions which suggest corresponding enhanced nonlinear molecular optical properties. Add…
NHC-Based Iron Sensitizers for DSSCs
2018
International audience; Nanostructured dye-sensitized solar cells (DSSCs) are promising photovoltaic devices because of their low cost and transparency. Ruthenium polypyridine complexes have long been considered as lead sensitizers for DSSCs, allowing them to reach up to 11% conversion efficiency. However, ruthenium suffers from serious drawbacks potentially limiting its widespread applicability, mainly related to its potential toxicity and scarcity. This has motivated continuous research efforts to develop valuable alternatives from cheap earth-abundant metals, and among them, iron is particularly attractive. Making iron complexes applicable in DSSCs is highly challenging due to an ultrafa…
Excited states engineering enables efficient near-infrared lasing in nanographenes
2021
The spectral overlap between stimulated emission (SE) and absorption from dark states (i.e. charges and triplets) especially in the near-infrared (NIR), represents one of the most effective gain loss channel in organic semiconductors. Recently, bottom-up synthesis of atomically precise graphene nanostructures, or nanographenes (NGs), has opened a new route for the development of environmentally and chemically stable materials with optical gain properties. However, also in this case, the interplay between gain and absorption losses has hindered the attainment of efficient lasing action in the NIR. Here, we demonstrate that the introduction of two fluoranthene imide groups to the NG core lead…
The first large-scale shell-model calculation of the two-neutrino double beta decay of $^{76}$Ge to the excited states in $^{76}$Se
2022
Large-scale shell-model calculations were carried out for the half-lives and branching ratios of the $2\nu\beta\beta$ decay of $^{76}$Ge to the ground state and the lowest three excited states $2_1^+$, $0_2^+$ and $2_2^+$ in $^{76}$Se. In total, the wave functions of more than 10,000 intermediate $1^+$ states in $^{76}$As were calculated in a three-step procedure allowing an efficient use of the available computer resources. In the first step, 250 lowest states, below some 5 MeV of excitation energy, were calculated without truncations within a full major shell $0f_{5/2}-1p-0g_{9/2}$ for both protons and neutrons. The wave functions of the rest of the states, up to some 30 MeV, were compute…
Lifetime measurements of excited states in $^{162}$W and $^{164}$W and the evolution of collectivity in rare-earth nuclei
2017
International audience; Lifetimes of the first excited 2+ states in the extremely neutron-deficient $^{162}$W and $^{164}$W nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data for the isotopic chains of hafnium, tungsten, and osmium, from the midshell region near the β-stability line towards the N=82 closed shell and the most neutron-deficient nuclides, are compared with predictions of nuclear deformations and 21+→0g.s.+ reduced transition strengths from different classes of state-of-the-art theoretical model calculations. The results reveal striking differences and deficiencies in the predictive power of current nuclear structure models.
Lifetime measurements in 166Re : Collective versus magnetic rotation
2016
Lifetimes of excited states in the neutron-deficient odd-odd nucleus 166Re have been measured for the first time using the recoil distance Doppler-shift method. The measured lifetime for the (8−) state; τ = 480 (80) ps, enabled an assessment of the multipolarities of the γ rays depopulating this state. Information on electromagnetic transition strengths were deduced for the γ -ray transitions from the (9−), (10−), and (11−) states, and in the case of the (10−) and (11−) states limits on the B(M1) and B(E2) strengths were estimated. The results are compared with total Routhian surface predictions and semiclassical calculations. Tilted-axis cranking calculations based on a relativistic mean-f…
Excited-state absorption in erbium-doped silica fiber with simultaneous excitation at 977 and 1531 nm
2009
We report a study of the excited-state absorption (ESA) in erbium-doped silica fiber (EDF) pumped at 977 nm, when the fiber is simultaneously excited by signal radiation at 1531 nm. We show, both experimentally and theoretically, that ESA efficiency at 977 nm gets strongly enhanced only in the presence of signal power. Experimentally, this conclusion is supported through the detection of upconversion emission, a “fingerprint” of the ESA process, and through the measurements of the EDF nonlinear transmission coefficient for the pump wavelength, which is sensitive to the ESA value. It is shown that the experimental data are precisely modeled with an advanced five-level Er3+ model developed fo…