Inner-shell photodetachment from Ni− : A giant Feshbach resonance

Citation: Dumitriu, I., Bilodeau, R. C., Gorczyca, T. W., Walter, C. W., Gibson, N. D., Rolles, D., … Berrah, N. (2017). Inner-shell photodetachment from \mathrm{N}{\mathrm{i}}^{\ensuremath{-}}: A giant Feshbach resonance. Physical Review A, 96(2), 023405. https://doi.org/10.1103/PhysRevA.96.023405Inner-shell photodetachment from Ni−([Ar]3d94s2) leading to Ni+,Ni2+, and Ni3+ ion production was studied near and above the 3p excitation region, in the 60–90 eV photon energy range, using a merged ion-photon beam technique. The absolute photodetachment cross section of Ni− leading to Ni+ ion production was measured. The 3p→3d photoexcitation in Ni− gives rise to a giant Feshbach resonance. In the near-threshold region, a Fano profile, modified by a Wigner s-wave (l=0) threshold law, accurately fits the Ni− single-photodetachment cross section. A lower-order R-matrix calculation shows overall agreement with essential features of the experimental data, confirming the nature of the strong, asymmetric Fano profile of the giant 3p→3d photoexcitation-autodetachment resonance in Ni−

Glucocorticoids, master modulators of the thymic catecholaminergic system?

There is evidence that the major mediators of stress, i.e., catecholamines and glucocorticoids, play an important role in modulating thymopoiesis and consequently immune responses. Furthermore, there are data suggesting that glucocorticoids influence catecholamine action. Therefore, to assess the putative relevance of glucocorticoid-catecholamine interplay in the modulation of thymopoiesis we analyzed thymocyte differentiation/maturation in non-adrenalectomized and andrenalectomized rats subjected to treatment with propranolol (0.4 mg.100 g body weight(-1).day(-1)) for 4 days. The effects of beta-adrenoceptor blockade on thymopoiesis in non-adrenalectomized rats differed not only quantitatively but also qualitatively from those in adrenalectomized rats. In adrenalectomized rats, besides a more efficient thymopoiesis [judged by a more pronounced increase in the relative proportion of the most mature single-positive TCR alpha beta(high) thymocytes as revealed by two-way ANOVA; for CD4(+)CD8(-)F (1,20) = 10.92, P lt 0.01; for CD4(-)CD8(+)F (1,20) = 7.47, P lt 0.05], a skewed thymocyte maturation towards the CD4(-)CD8(+) phenotype, and consequently a diminished CD4(+)CD8(-)/CD4(-)CD8(+) mature TCR alpha beta(high) thymocyte ratio (3.41 +/- 0.21 in non-adrenalectomized rats vs 2.90 +/- 0.31 in adrenalectomized rats, P lt 0.05) were found. Therefore, we assumed that catecholaminergic modulation of thymopoiesis exhibits a substantial degree of glucocorticoid-dependent plasticity. Given that glucocorticoids, apart from catecholamine synthesis, influence adrenoceptor expression, we also hypothesized that the lack of adrenal glucocorticoids affected not only beta-adrenoceptor- but also alpha-adrenoceptor-mediated modulation of thymopoiesis

Estimation of target strength of Sardina pilchardus and Sardinella aurita by theoretical approach

The target strength (TS) patterns of Sardina pilchardus and Sardinella aurita at 38 and 120 kHz were estimated by a prolate-spheroid model, using measurements of swimbladder length and width. The ratio of swimbladder length to total length (TL) was similar in both species, however the ratio of swimbladder width to TL was smaller and more variable for S. aurita. Assuming a normal distribution of fish swimming orientation angle (θfish) with mean ± standard deviation (SD) of 0 ± 10°, the normalized (by TL) average TS (b20) was estimated to be -64.0 dB (38 kHz) and -65.2 dB (120 kHz) for S. pilchardus, and -66.2 dB (38 kHz) and -67.2 dB (120 kHz) for S. aurita. Compared with currently applied b20 values at 38 kHz, our results under four different θfish assumptions (0 ± 10°, 0 ± 15°, -5 ± 10°, and -5 ± 15°) were 6-9 dB higher for S. pilchardus and 5-7 dB higher for S. aurita. This suggests four- to eightfold overestimation risk for S. pilchardus and three- to fivefold overestimation risk for S. aurita when using the currently applied b20 values

Two-photon coincidence studies of highly-charged ion relaxation in solids

We studied the relaxation of hollow atoms by two-photon transitions during the stopping of slow (E=8.5q keV) highly charged Pbq+ (q=53–58) ions in a thin Ta foil. The X-rays emitted during the relaxation process were detected in coincidence with two Si(Li) detectors. Particular attention was paid to the role of the internal dielectronic excitation (IDE) in the relaxation dynamics. We found a clear contribution to relaxation by the IDE process also for projectiles with initial M-shell vacancies and IDE speeds up relaxation of electrons from high Rydberg states by directly filling vacancies in the N-shell that is accompanied with the excitation of M-shell electrons. We discuss the relaxation mechanism, and present results for the fluorescence yield and the IDE probability of highly charged Pb ions in a solid

Site-selective ionization and relaxation dynamics in heterogeneous nanosystems

We investigated energy and charge transfer mechanisms as well as fragmentation dynamics in site-selectively ionized heterogeneous core-shell clusters using a high-resolution photoelectron-ion coincidence technique. We show that after inner-shell photoionization, energy or charge is transferred to neighboring atoms and that the subsequent charge localization depends on the site of ionization. Cluster bulk ionization leads to more distinct fragmentation channels than surface ionization. We attribute this to different electronic decay, charge localization, and fragmentation times and conclude that charge transfer and fragmentation dynamics are strongly influenced by the environment of the initially ionized atom

Inner-shell photodetachment from Ni−: A giant Feshbach resonance

Inner-shell photodetachment from Ni−([Ar]3d94s2) leading to Ni+,Ni2+, and Ni3+ ion production was studied near and above the 3p excitation region, in the 60–90 eV photon energy range, using a merged ion-photon beam technique. The absolute photodetachment cross section of Ni− leading to Ni+ ion production was measured. The 3p→3d photoexcitation in Ni− gives rise to a giant Feshbach resonance. In the near-threshold region, a Fano profile, modified by a Wigner s-wave (l=0) threshold law, accurately fits the Ni− single-photodetachment cross section. A lower-order R-matrix calculation shows overall agreement with essential features of the experimental data, confirming the nature of the strong, asymmetric Fano profile of the giant 3p→3d photoexcitation-autodetachment resonance in Ni−