Control of near-threshold detachment cross sections via laser polarization

The behavior of near-threshold cross sections for dissociation of a target into a pair of particles, as described by Wigner's threshold law, can depend sensitively on the angular momentum of the particles. In this Letter, we investigate the near-threshold nonresonant two-photon detachment process in the negative ion of gold. The expected s-wave threshold behavior is observed with linearly polarized light. Closure of the s-wave channel is realized by using circular polarization, allowing the first observation of a d-wave threshold. Practical applications are discussed, including extensions which could prove valuable for investigations of negative ions with near-threshold structure.     

Chalcogen arsenide clusters of iron with a functional carboxyl group: Synthesis, structures, and thermolysis

The carbonyl clusters [Fe₃(??₃-Q)(??₃-AsR)(CO)₉] (Q = Se and Te; R = meta- and para-HOOCC₆H₄) were obtained from the salts K₂[Fe₃(??₃-Q)(CO)₉] and organoarsenic diiodides RAsI₂ prepared by reducing iodination of arsonic acids RAsO(OH)₂ according to a novel method. The structures of the clusters were identified by X-ray diffraction. The crystal packing motifs of the dimers of the cluster molecules and their relationship with the solubility of the clusters are discussed. The sequential steps of the thermolysis (decarbonylation, decarboxylation, and decomposition of the organic fragment) of the clusters were studied. The presence and location of the carboxyl group does not influence the decarbonylation temperature.     

Conductance and vibrational states of single-molecule junctions controlled by mechanical stretching and material variation

The changes of molecular conformation, contact geometry, and metal-molecule bonding are revealed by inelastic-electron-tunneling spectroscopy measurements characterizing the molecular vibrational modes and the metal-phonon modes in alkanedithiol molecular junctions at low temperature. Combining inelastic-electron-tunneling spectroscopy with mechanical control and electrode material variation (Au or Pt) enables separating the influence of contact geometry and of molecular conformation. The mechanical strain of different electrode materials can be imposed onto the molecule, opening a new route for controlling the charge transport through individual molecules.     

Selective Formation and Unusual Reactivity of Tetraarsabicyclo[1.1.0]butane Complexes

The selective formation of the dinuclear butterfly complexes [{Cp′′′Fe(CO)₂}₂(μ,η^1:1‐E₄)] (E=P ( 1 a ), As ( 1 b )) and [{Cp*Cr(CO)₃}₂(μ,η^1:1‐E₄)] (E=P ( 2 a ), As ( 2 b )) as new representatives of this rare class of compounds was found by reaction of E₄ with the corresponding dimeric carbonyl complexes. Complexes 1 b and 2 b are the first As₄ butterfly compounds with a bridging coordination mode. Moreover, first studies regarding the reactivity of 1 b and 2 b are presented, revealing the formation of the unprecedented As₈ cuneane complexes [{Cp′′′Fe(CO)₂}₂{Cp′′′Fe(CO)}₂(μ₄,η^1:1:2:2‐As₈)] ( 3 b ) and [{Cp*Cr(CO)₃}₄(μ₄,η^1:1:1:1‐As₈)] ( 4 ). The compounds are fully characterized by NMR and IR spectroscopy as well as by X‐ray structure analysis. In addition, DFT calculations give insight into the transformation pathway from the E₄ butterfly to the corresponding cuneane structural motif.     

TWO DIFFERENT TYPES OF PHOTOCHEMISTRY IN PHYCOERYTHROCYANIN α-SUBUNIT*

The photochemical activities of phycoerythrocyanin α-subunits from Mastigocladus laminosus separated by isoelectric focusing were tested by irradiating at 500, 550, 577 and 600 nm. Two types of photoreversible photochromic responses have been characterized by absorption and absorption difference spectroscopy. Type I is the well-known absorption shift from 571 to 506 nm. Type II is a new response characterized by a line-broadening of the 570 nm absorption.     

ORIGIN OF THE RED SHIFTED ABSORPTION IN PHYCOCYANIN 632 FROM Mastigocladus laminosus

A phycocyanin (PC) with γ_max= 632 nm (PC632) was isolated from extracts of the cyanobacterium Mastigocladus laminosus. The complex contained three polypeptides migrating in SDS-PAGE around 22 kDa. The N-termini of the three polypeptides are identical. They are homologous to rod-core linker polypeptides from this and another cyanobacterium and are identical to one of them. Reconstitution of PC (γ_max=614–620 nm) with the 22 kDa polypeptide produced again the red-shifted PC632. Phycobilisomes isolated at pH 6 or 7 contain, if any, only traces of 22 kDa polypeptides. Origin and functions of the polypeptides are discussed, they are most likely proteolytic fragments of allophycocyanin-PC rod-core linkers that contain the PC-binding domain.