Low temperature scanning force microscopy of the Si(111)-(7x7) surface

A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- (7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few A of the surface.     

C-N bond formation via ligand-induced nucleophilicity at a coordinated triamidoamine ligand

Reaction of (N(3)N)ZrX complexes (X = amido, Cl(-), CH(3)(-)) with carbodiimide substrates results in insertion into an Zr-N bond of the triamidoamine ligand rather than the Zr-X bond as has been observed for related (N(3)N)ZrX complexes (X = PR(2)(-), AsR(2)(-)).     

Application of novel technology to the abe fermentation process

Applied Biochemistry and Biotechnology - Traditional technology for ABE production and recovery does not allow an economic process. However, use of a fluidized-bed reactor using immobilized cells...     

Chemical imaging of single 4,7,12,15-tetrakis[2.2]paracyclophane by spatially resolved vibrational spectroscopy

Single 4,7,12,15-tetrakis[2.2]paracyclophane were deposited on NiAl(110) surface at 11 K. Two adsorbed species with large and small conductivities were detected by the scanning tunneling microscope (STM). Their vibrational properties were investigated by inelastic electron tunneling spectroscopy (IETS) with the STM. Five vibrational modes were observed for the species with the larger conductivity. The spatially resolved vibrational images for the modes show striking differences, depending on the coupling of the vibrations localized on different functional groups within the molecule to the electronic states of the molecule. The vibrational modes are assigned on the basis of ab initio calculations. No IETS signal is resolved from the species with the small conductivity.     

Optical coherence and theoretical study of the excitation dynamics of a highly symmetric cyclophane-linked oligophenylenevinylene dimer

Optoelectronic properties of a polyphenylenevinylene-based oligomer and its paracylophane-linked dimer are studied using a variety of experimental and theoretical techniques. Despite the symmetrical structure and redshifted absorption of the dimer versus the monomer, an exciton picture is not the most appropriate. Electronic structure calculations establish changes in charge density upon optical excitation and show localized excitations that cannot be accounted for by a simple Frenkel exciton model. Visible frequency pump-probe anisotropy measurements suggest that the dimer should be considered as a three-level system with a fast, approximately 130 fs, internal conversion from the higher to lower energy excited electronic state. Signatures of nuclear relaxation processes are compared for electric field-resolved transient grating and two-dimensional photon echo spectra. These measurements reveal that nuclear relaxation occurs on similar time scales for the monomer and dimer. The connection between the spectral phase of four-wave mixing signals and the time dependent width of a nuclear wave packet is discussed. Semiempirical electronic structure and metropolis Monte Carlo calculations show that the dominant line broadening mechanisms for the monomer and dimer are associated with inter-ring torsional coordinates. Together, the theoretical calculations and electric field-resolved four-wave mixing experiments suggest that while the structure of dimer is more rigid than that of monomer, the difference in their rigidities is not sufficient to slow down excited state relaxation of dimer with respect to the monomer.