Mn -Acetate Complexes Studied as Single Molecules.

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn coordination clusters of general formula [Mn Mn O (RCOO) (H O) ] had been exemplified by bulk samples of the archetypal [Mn Mn O (CH COO) (H O) ] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn O (CH COO) (CH CN)] (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn O (CH COO) (CH CN)] (1), [Mn O (CH COO) ] (2), [Mn O (CH COO) (H O) ] (3), and the complex in bulk geometry [Mn Mn O (CH COO) (H O) ] (5).

Soft X-ray Spectroscopy as a Probe for Gas-Phase Protein Structure: Electron Impact Ionization from Within.

Preservation of protein conformation upon transfer into the gas phase is key for structure determination of free single molecules, for example using X-ray free-electron lasers. In the gas phase, the helicity of melittin decreases strongly as the protein's protonation state increases. We demonstrate the sensitivity of soft X-ray spectroscopy to the gas-phase structure of melittin cations ([melittin+qH] , q=2-4) in a cryogenic linear radiofrequency ion trap.

Size-Dependent Ligand Quenching of Ferromagnetism in Co(benzene) Clusters Studied with X-ray Magnetic Circular Dichroism Spectroscopy.

Cobalt-benzene cluster ions of the form Co(bz) (n = 0-3) were produced in the gas phase, mass-selected, and cooled in a cryogenic ion trap held at 3-4 K. To explore ligand effects on cluster magnetic moments, these species were investigated with X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. XMCD spectra yield both the spin and orbital angular momenta of these clusters.

Maximum spin polarization in chromium dimer cations as demonstrated by X-ray magnetic circular dichroism spectroscopy.

X-ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr2 (+) . Our results indicate that the removal of a single electron from the 4sσg bonding orbital of Cr2 drastically changes the preferred coupling of the 3d electronic spins. While the neutral molecule has a zero-spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of S=11/2, and almost twice the bond length of the neutral molecule.

A multicoincidence study of fragmentation dynamics in collision of γ-aminobutyric acid with low-energy ions.

Fragmentation of the γ-aminobutyric acid molecule (GABA, NH(2)(CH(2))(3)COOH) following collisions with slow O(6+) ions (v≈0.3 a.u.

Ion-induced fragmentation of amino acids: effect of the environment.

In general, radiation-induced fragmentation of small amino acids is governed by the cleavage of the C-C(α) bond. We present results obtained with 300 keV Xe(20+) ions that allow molecules (glycine and valine) to be ionised at large distances without appreciable energy transfer. Also in the present case, the C-C(α) bond turns out to be the weakest link and hence its scission is the dominant fragmentation channel.