Excited states of the water molecule : Analysis of the valence and Rydberg character

The excited states of the water molecule have been analyzed by using the extended quantum-chemical multistate CASPT2 method, namely, MS-CASPT2, in conjunction with large one-electron basis sets of atomic natural orbital type. The study includes 13 singlet and triplet excited states, both valence and 3s-, 3p-, and 3d-members of the Rydberg series converging to the lowest ionization potential and the 3s- and 3p-Rydberg members converging to the second low-lying state of the cation, 1 math. The research has been focused on the analysis of the valence or Rydberg character of the low-lying states. The computation of the 1 math state of water at different geometries indicates that it has a predominant 3s-Rydberg character at the equilibrium geometry of the molecule but it becomes progressively a valence state described mainly by the one-electron 1b1→4a1 promotion, as expected from a textbook of general chemistry, upon elongation of the O–H bonds. The described valence-Rydberg mixing is established to be originated by a molecular orbital (MO) Rydbergization process, as suggested earlier by R. S. Mulliken [Acc. Chem. Res. 9, 7 (1976)] . The same phenomenon occurs also for the 1 math state whereas a more complex behavior has been determined for the 2 math state, where both MO Rydbergization and configurational mixing take place. Similar conclusions have been obtained for the triplet states of the [email protected] [email protected] [email protected]

Two-dimensional two-component plasma with adsorbing impurities

We study the behavior of the two-dimensional two-component plasma in the presence of some adsorbing impurities. Using a solvable model, we find analytic expressions for the thermodynamic properties of the plasma such as the $n$-body densities, the grand potential, and the pressure. We specialize in the case where there are one or two adsorbing point impurities in the plasma, and in the case where there are one or two parallel adsorbing lines. In the former case we study the effective interaction between the impurities, due to the charge redistribution around them. The latter case is a model for electrodes with adsorbing sticky sites on their surface

Computation of conical intersections by using perturbation techniques

Multiconfigurational second-order perturbation theory, both in its single-state multiconfigurational second-order perturbation theory (CASPT2) and multistate (MS-CASPT2) formulations, is used to search for minima on the crossing seams between different potential energy hypersurfaces of electronic states in several molecular systems. The performance of the procedures is tested and discussed, focusing on the problem of the nonorthogonality of the single-state perturbative solutions. In different cases the obtained structures and energy differences are compared with available complete active space self-consistent field and multireference configuration interaction solutions. Calculations on different state crossings in LiF, formaldehyde, the ethene dimer, and the penta-2,4-dieniminium cation illustrate the discussions. Practical procedures to validate the CASPT2 solutions in polyatomic systems are explored, while it is shown that the application of the MS-CASPT2 procedure is not straightforward and requires a careful analysis of the stability of the results with the quality of the reference wave functions, that is, the size of the active [email protected] [email protected] [email protected]

Retención de agua en musgos de páramo de los municipios de Siachoque, Toca y Pesca (Boyacá)

Los musgos cumplen un papel importante en el ecosistema debido a su estructura morfológica para retener cantidades considerables de agua y mejorar los contenidos de humedad en el suelo. Sin embargo, el alto impacto del hombre en los páramos disminuye notablemente la población de los musgos y la conservación del recurso agua. Se evaluó la capacidad hídrica de muestras colectadas en los páramos de los municipios de Pesca, Siachoque y Toca (Boyacá) en diferentes sustratos (roca, suelo y corteza de árbol o epifitas). Se realizó un diseño completamente al azar y se determinó la capacidad hídrica en seco y en fresco. Se encontró que la familia con mayor número de muestras colectadas fue la Sphagnaceae en los páramos de los municipios de Pesca y Siachoque. Las muestras de musgos colectadas que poseen el mayor contenido de agua fueron las encontradas en el páramo del municipio de Pesca, mientras que las muestras colectadas en el municipio de Toca mostraron una gran variedad de familias de musgos (Leucomiaceae, Dicranaceae, Orthortrichaceae, Bartramyaceae) en menor población y con un menor contenido de agua. Además se presentó un mayor contenido de agua en las muestras colectadas del sustrato suelo que en las colectadas en roca y en epifitas, de ahí la importancia de las condiciones climáticas de cada una de las zonas en los diferentes municipios estudiados, pues afectan la retención de agua por parte de los musgos

Toward the understanding of DNA fluorescence : The singlet excimer of cytosine

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 [email protected] [email protected] [email protected] [email protected]

Ab initio determination of the ionization potentials of DNA and RNA nucleobases

Quantum chemical high level ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute vertical and adiabatic ionization potentials of the five canonical DNA and RNA nucleobases: uracil, thymine, cytosine, adenine, and guanine. Several states of their cations have been also calculated. The present results represent a systematic compendium of these magnitudes, establishing theoretical reference values at a level not reported before, calibrating computational strategies, and guiding the assignment of the features in the experimental photoelectron [email protected] [email protected] [email protected] [email protected]

Tryptophan depletion affects compulsive behaviour in rats:strain dependent effects and associated neuromechanisms

RATIONALE: Compulsive behaviour, present in different psychiatric disorders, such as obsessive-compulsive disorder, schizophrenia and drug abuse, is associated with altered levels of monoamines, particularly serotonin (5-hydroxytryptamine) and its receptor system. OBJECTIVES: The present study investigated whether 5-HT manipulation, through a tryptophan (TRP) depletion by diet in Wistar and Lister Hooded rats, modulates compulsive drinking in schedule-induced polydipsia (SIP) and locomotor activity in the open-field test. The levels of dopamine, noradrenaline, serotonin and its metabolite were evaluated, as well as the 5-HT(2A) and 5-HT(1A) receptor binding, in different brain regions. METHODS: Wistar rats were selected as high (HD) or low (LD) drinkers according to their SIP behaviour, while Lister hooded rats did not show SIP acquisition. Both strains were fed for 14 days with either a TRP-free diet (T−) or a TRP-supplemented diet (T+) RESULTS: The TRP depletion diet effectively reduced 5-HT levels in the frontal cortex, amygdala and hippocampus in both strains of rats. The TRP-depleted HD Wistar rats were more sensitive to 5-HT manipulation, exhibiting more licks on SIP than did the non-depleted HD Wistar rats, while the LD Wistar and the Lister Hooded rats did not exhibit differences in SIP. In contrast, the TRP-depleted Lister Hooded rats increased locomotor activity compared to the non-depleted rats, while no differences were found in the Wistar rats. Serotonin 2A receptor binding in the striatum was significantly reduced in the TRP-depleted HD Wistar rats. CONCLUSIONS: These results suggest that alterations of the serotonergic system could be involved in compulsive behaviour in vulnerable populations

Galaxy Pairs in the 2dF Survey I. Effects of Interactions in the Field

We study galaxy pairs in the field selected from the 100 K public release of the 2dF galaxy redshift survey. Our analysis provides a well defined sample of 1258 galaxy pairs, a large database suitable for statistical studies of galaxy interactions in the local universe, $z \le 0.1$. Galaxy pairs where selected by radial velocity ($\Delta V$) and projected separation ($r_{\rm p}$) criteria determined by analyzing the star formation activity within neighbours (abridged). The ratio between the fractions of star forming galaxies in pairs and in isolation is a useful tools to unveil the effects of having a close companion. We found that about fifty percent of galaxy pairs do not show signs of important star formation activity (independently of their luminosities) supporting the hypothesis that the internal properties of the galaxies play a crucial role in the triggering of star formation by interactions.Comment: 9 pages, 11 Postscript figures. Submitted to MNRAS. Revised versio