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A one parameter, semi-empirical formula for Λ-binding energy of heavy hypernuclei in the inverse powers of core mass number (A c) has been developed in the framework of the folding model. Unlike similar calculations reported by other authors (Deloff 1971; Daskaloyanniset al 1985), we are able to take into account the effect arising from the difference in the number of protons and neutrons of the core nuclei having same mass number. The radius and diffuseness are parametrized using the experimentally known charge density data of a fairly large number of medium and heavy nuclei. The well depth parameter (i.e. Λ-binding energy in infinite nuclear matter) in the formula is obtained from a fit to theB Λ data of Λ 28 Si, Λ 40 Ca, Λ 51 V and Λ 39 Y. Using the original Λ-nucleus potential, theB Λ of ground and the experimentally known excited states of these hypernuclei have also been calculated by solving numerically the two-body Schrödinger equation. The agreement with the experimental data is satisfactory. 相似文献
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Kamrath MZ Garand E Jordan PA Leavitt CM Wolk AB Van Stipdonk MJ Miller SJ Johnson MA 《Journal of the American Chemical Society》2011,133(16):6440-6448
We present infrared photodissociation spectra of two protonated peptides that are cooled in a ~10 K quadrupole ion trap and "tagged" with weakly bound H(2) molecules. Spectra are recorded over the range of 600-4300 cm(-1) using a table-top laser source, and are shown to result from one-photon absorption events. This arrangement is demonstrated to recover sharp (Δν ~6 cm(-1)) transitions throughout the fingerprint region, despite the very high density of vibrational states in this energy range. The fundamentals associated with all of the signature N-H and C=O stretching bands are completely resolved. To address the site-specificity of the C=O stretches near 1800 cm(-1), we incorporated one (13)C into the tripeptide. The labeling affects only one line in the complex spectrum, indicating that each C=O oscillator contributes a single distinct band, effectively "reporting" its local chemical environment. For both peptides, analysis of the resulting band patterns indicates that only one isomeric form is generated upon cooling the ions initially at room temperature into the H(2) tagging regime. 相似文献
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We report the vibrational predissociation spectrum of C(5)H(5)N-CO(2)(-), a radical anion which is closely related to the key intermediates postulated to control activation of CO(2) in photoelectrocatalysis with pyridine (Py). The anion is prepared by the reaction of Py vapor with (CO(2))(m)(-) clusters carried out in an ionized, supersonic entrainment ion source. Comparison with the results of harmonic frequency calculations establishes that this species is a covalently bound molecular anion derived from the corresponding carbamate, C(5)H(5)N-CO(2)(-) (H(+)). These results confirm the structural assignment inferred in an earlier analysis of the cluster distributions and photoelectron spectra of the mixed Py(m)(CO(2))(n)(-) complexes [J. Chem. Phys. 2000, 113 (2), 596-601]. The spectra of the (CO(2))(m)(-) (m = 5 and 7) clusters are presented for the first time in the lower energy range (1000-2400 cm(-1)), which reveal several of the fundamental modes that had only been characterized previously by their overtones and combination bands. Comparison of these new spectra with those displayed by Py(CO(2))(n)(-) suggests that a small fraction of the Py(CO(2))(n)(-) ions are trapped entrance channel reaction intermediates in which the charge remains localized on the (CO(2))(m)(-) part of the cluster. 相似文献
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Leavitt CM Wolk AB Kamrath MZ Garand E Van Stipdonk MJ Johnson MA 《Journal of the American Society for Mass Spectrometry》2011,22(11):1941-1952
We report vibrational predissociation spectra of the four protonated dipeptides derived from glycine and sarcosine, GlyGlyH+•(H2)1,2, GlySarH+•(D2)2, SarGlyH+•(H2)2, and SarSarH+•(D2)2, generated in a cryogenic ion trap. Sharp bands were recovered by monitoring photoevaporation of the weakly bound H2 (D2) molecules in a linear action regime throughout the 700–4200 cm–1 range using a table-top laser system. The spectral patterns were analyzed in the context of the low energy structures obtained
from electronic structure calculations. These results indicate that all four species are protonated on the N-terminus, and
feature an intramolecular H-bond involving the amino group. The large blue-shift in the H-bonded N–H fundamental upon incorporation
of a methyl group at the N-terminus indicates that this modification significantly lowers the strength of the intramolecular
H-bond. Methylation at the amide nitrogen, on the other hand, induces a significant rotation (~110o) about the peptide backbone. 相似文献
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Garand E Fournier JA Kamrath MZ Schley ND Crabtree RH Johnson MA 《Physical chemistry chemical physics : PCCP》2012,14(29):10109-10113
We report the vibrational predissociation spectra of two related organometallic half-sandwich iridium species which have been recently reported as activated intermediates in the context of homogenous water oxidation. These compounds are extracted from solution into a cryogenic photofragmentation mass spectrometer and "tagged" with weakly bound H(2) molecules that do not significantly perturb the intrinsic structures of the ions. The resulting spectra display very sharp (~5 cm(-1)), well-resolved bands that provide a stringent test for electronic structure calculations, and are accurately recovered by harmonic predictions for the bare species. The spectra reveal subtle distortions of the ligand structure when a solvent molecule (acetonitrile) is directly coordinated with the metal center. 相似文献
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