235 research outputs found
The electronic spectra of protonated PANH molecules
Aims. This study was designed to examine the viability of protonated
nitrogen-substituted polycyclic aromatic hydrocarbons (H+PANHs) as candidates
for the carriers of the diffuse interstellar bands (DIBs). Methods. We obtained
the electronic spectra of two protonated PANH cations, protonated acridine and
phenanthridine, using parent ion photo-fragment spectroscopy and generated
theoretical electronic spectra using ab initio calculations. Results. We show
that the spectra of the two species studied here do not correspond to known
DIBs. However, based on the general properties derived from the spectra of
these small protonated nitrogen-substituted PAHs, we propose that larger H+PANH
cations represent good candidates for DIB carriers due to the expected
positions of their electronic transitions in the UV-visible and their narrow
spectral bands.Comment: 7 pages, 2 figures, accepted for publication in A&
SUSY Quantum Mechanics with Complex Superpotentials and Real Energy Spectra
We extend the standard intertwining relations used in Supersymmetrical (SUSY)
Quantum Mechanics which involve real superpotentials to complex
superpotentials. This allows to deal with a large class of non-hermitean
Hamiltonians and to study in general the isospectrality between complex
potentials. In very specific cases we can construct in a natural way
"quasi-complex" potentials which we define as complex potentials having a
global property such as to lead to a Hamiltonian with real spectrum. We also
obtained a class of complex transparent potentials whose Hamiltonian can be
intertwined to a free Hamiltonian. We provide a variety of examples both for
the radial problem (half axis) and for the standard one-dimensional problem
(the whole axis), including remarks concerning scattering problems.Comment: 22 pages, Late
Pseudoscalar-scalar transition form factors in covariant light front dynamics
In an explicitly covariant light-front formalism, we analyze transition form
factors between pseudoscalar and scalar mesons. Application is performed in
case of the transition in the full available transfer momentum
range .Comment: 4 pages, 4 figures. Talk given at the XXXIII International Conference
on High Energy Physics, ICHEP06, Moscow, 26 July-02 Augus
Form factors in B->f0(980) and D->f0(980) transitions from dispersion relations
Within the dispersion relation approach we give the double spectral
representation for space-like and time-like B-> f_0(980) and D-> f_0(980)
transition form factors in the full q^2 range. The spectral densities, being
the input of the dispersion relations, are obtained from a triangle diagram in
the relativistic quark model.Comment: Talk given at MESON 2006, Krakow, 9-13 June 200
Scalar resonances in a unitary -wave model for
We propose a model for decays following
experimental results which indicate that the two-pion interaction in the
-wave is dominated by the scalar resonances and
. The weak decay amplitude for , where is a
resonance that subsequently decays into , is constructed in a
factorization approach. In the -wave, we implement the strong decay by means of a scalar form factor. This provides a unitary
description of the pion-pion interaction in the entire kinematically allowed
mass range from threshold to about 3 GeV. In order to
reproduce the experimental Dalitz plot for \Dppp, we include contributions
beyond the -wave. For the -wave, dominated by the , we use a
Breit-Wigner description. Higher waves are accounted for by using the usual
isobar prescription for the and . The major
achievement is a good reproduction of the experimental
distribution, and of the partial as well as the total \Dppp branching ratios.
Our values are generally smaller than the experimental ones. We discuss this
shortcoming and, as a byproduct, we predict a value for the poorly known transition form factor at .Comment: 23 pages, 2 figures. Two new equations. The value for the strength of
the contribution of the scalar form factor now agrees with other results in
the literature. Main results unchanged. Version to appear in Phys. Rev.
Communication: UV photoionization of cytosine catalyzed by Ag+
The photo-induced damages of DNA in interaction with metal cations, which are found in various environments, still remain to be characterized. In this paper, we show how the complexation of a DNA base (cytosine (Cyt)) with a metal cation (Ag+) changes its electronic properties. By means of UV photofragment spectroscopy of cold ions, it was found that the photoexcitation of the CytAg+ complex at low energy (315-282) nm efficiently leads to ionized cytosine (Cyt+) as the single product. This occurs through a charge transfer state in which an electron from the p orbital of Cyt is promoted to Ag+, as confirmed by ab initio calculations at the TD-DFT/B3LYP and RI-ADC(2) theory level using the SV(P) basis set. The low ionization energy of Cyt in the presence of Ag+ could have important implications as point mutation of DNA upon sunlight exposition.Fil: Taccone, MartĂn Ignacio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; ArgentinaFil: FĂ©raud, Geraldine. Aix Marseille UniversitĂ©. Physique des Interactions Ioniques et MolĂ©culaires; FranciaFil: Berdakin, Matias. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; ArgentinaFil: Dedonder Lardeux, Claude. Aix Marseille UniversitĂ©. Physique des Interactions Ioniques et MolĂ©culaires; FranciaFil: Jouvet, Christophe. Physique des Interactions Ioniques et MolĂ©culaires; FranciaFil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; Argentin
Non-radiative processes in protonated diazines, pyrimidine bases and an aromatic azine
International audienceThe excited state lifetimes of DNA bases are often very short due to very efficient non-radiative processes assigned to the pp*ânp* coupling. A set of protonated aromatic diazine molecules (pyridazine, pyrimidine and pyrazine C4H5N2+) and protonated pyrimidine DNA bases (cytosine, uracil and thymine), as well as the protonated pyridine (C5H6N+), have been investigated. For all these molecules except one tautomer of protonated uracil (enolâketo), electronic spectroscopy exhibits vibrational line broadening. Excited state geometry optimization at the CC2 level has been conducted to find out whether the excited state lifetimes measured from line broadening can be correlated to the calculated ordering of the pp* and np* states and the pp*ânp* energy gap. The short lifetimes, observed when one nitrogen atom of the ring is not protonated, can be rationalized by relaxation of the pp* state to the np* state or directly to the electronic ground state through ring puckering
Final state interactions in B+- to K+ K- K+- decays
Charged B decays to three charged kaons are analysed in the framework of the
QCD factorization approach. The strong final state K+K-interactions are
described using the kaon scalar and vector form factors. The scalar non-strange
and strange form factors at low K+K- effective masses are constrained by chiral
perturbation theory and satisfy the two-body unitarity conditions. The latter
stem from the properties of the meson-meson amplitudes which describe all
possible S-wave transitions between three coupled channels consisting of two
kaons, two pions and four pions. The vector form factors are fitted to the data
on the electromagnetic kaon interactions. The model results are compared with
the Belle and BaBar data. Away from phi(1020) resonance, in the S-wave
dominated K+K- mass spectra, a possibility for a large CP asymmetry is
identified.Comment: 7 pages, 4 figures, modified version published in Physics Letters
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