Outer-Sphere Electron Transfer in Methylene Chloride: Concentration, Salt, and Temperature Dependences of the Oxidation of beta-Re(2)X(4)(cis-1,2-bis(diphenylphosphino)ethylene)(2) (X = Cl, Br) by [Co(dimethylglyoximate)(3)(BF)(2)]BF(4) and the Oxidation of Re(2)Br(4)(PMe(2)Ph)(4) by [Co(1,2-cyclohexanedione dioximate)(3)(BBu)(2)]BF(4)

The kinetics of the oxidation of beta-Re(2)X(4)(cis-1,2-bis(diphenylphosphino)ethylene)(2) (X = Cl, Br) by the cobalt clathrochelate [Co(dimethylglyoximate)(3)(BF)(2)]BF(4) and the oxidation of Re(2)Br(4)(PMe(2)Ph)(4) by the cobalt clathrochelate [Co(1,2-cyclohexanedione dioximate)(3)(BBu)(2)]BF(4) have been studied by the stopped-flow method as a function of temperature (-85 to -19 degrees C), added Bu(4)NBF(4) (0-0.100 M), and reactant concentration in the low dielectric solvent methylene chloride. For each reaction, approximately 100 different conditions were studied. The observed rate constants were well fit by a mechanism involving separate paths for free ion and the ion-paired Co(III) oxidant. The analysis yielded values for DeltaH() and DeltaS() for each path of each reaction and consistent DeltaH degrees and DeltaS degrees values for the ion-pairing of the cationic reactant and the electrolyte. In addition, temperature-dependent electrochemical measurements in 0.10 M Bu(4)NBF(4) yielded DeltaH degrees and DeltaS degrees for the electron transfer process. This is the first measurement of the homogeneous electron transfer reactivity of the dirhenium complexes, and they showed the expected high reactivity. The most notable result is a very high inhibition (ca. 700-fold) by added salt of only the [Co(dmg)(3)(BF)(2)]BF(4) reactions. We attribute this to a change of rate-controlling step, for the ion-paired path, to one involving anion migration. This appears only to occur when the magnitude of ion-pairing free energy is significantly greater than the magnitude of the free energy change for the electron transfer process.     

Characterization of an actively linearized ultrabroadband chirped laser with a fiber-laser optical frequency comb

The optical frequency sweep of an actively linearized, ultrabroadband, chirped laser source is characterized through optical heterodyne detection against a fiber-laser frequency comb. Frequency sweeps were measured over approximately 5 THz bandwidths from 1530 nm to 1570 nm. The dominant deviation from linearity resulted from the nonzero dispersion of the fiber delay used as a reference for the sweep linearization. Removing the low-order dispersion effects, the residual sweep nonlinearity was less than 60 kHz rms, corresponding to a constant chirp with less than 15 ppb deviation across the 5 THz sweep.     

Modification of galvannealed steel through aluminum addition

Aluminum is believed to modify and to some extent control the coating characteristics of commercially produced galvanneal sheet steel. These include mechanical, chemical, and aesthetic properties. Whereas the aluminum added to the molten zinc bath is known to form intermetallics before the steel is annealed, our research is primarily concerned with the effect aluminum has on suppression or enhancement of the particular iron--zinc alloy phases in the coating during galvannealing. The microstructure of four commercially important iron--zinc intermetallic phases containing varying aluminum content between 0--1.5 weight percent has been studied. It is also believed that an iron--aluminum alloy, known as the inhibition layer, forms on the steel surface following hot dipping and prior to annealing. Transmission and scattering Mössbauer spectroscopy as well as X-ray diffraction have been used to identify iron--zinc and iron--aluminum alloys present in the coatings. Discussion will be presented on the effect aluminum has on phase suppression for Fe--Zn alloys prepared in commercially produced galvanneal.     

Self-adjoint subspace extensions of nondensely defined symmetric operators

The self-adjoint subspace extensions of a possibly nondensely defined symmetric operator in a Hilbert space are characterized in terms of “generalized boundary conditions.”     

Direct-comb molecular spectroscopy with accurate, resolved comb teeth over 43 THz

We demonstrate a dual-comb spectrometer using stabilized frequency combs spanning 177 to 220 THz (1360 to 1690 nm) in the near infrared. Comb-tooth-resolved measurements of amplitude and phase generate over 4×10(5) individually resolved spectral elements at 100 MHz point spacing and kilohertz-level resolution and accuracy. The signal-to-noise ratio is 100 to 3000 per comb tooth. Doppler-broadened phase and amplitude spectra of CO(2), CH(4), C(2)H(2), and H(2)O in a 30 m multipass cell agree with established spectral parameters, achieving high-resolution measurements with optical bandwidth generally associated with blackbody sources.     

Acetonitrile/water gas-phase reaction products observed by use of atmospheric pressure chemical ionization: adducts formed with sulfonamides

Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the two most common mass spectrometric ionization methods used in the pharmaceutical industry. However, APCI analysis can sometimes lead to ambiguity in compound characterization and quantitation due to gas-phase reactions occurring between acetonitrile and water in the plasma, and between these plasma-generated compounds and the analyte. During the analysis of various sultams and sulfonamides we observed signals corresponding to m/z [M+44](+) and [M+60](+). Various solvent conditions and collisionally activated dissociation MS(n) experiments revealed that under the high-energy plasma conditions of APCI, the acetonitrile/water solvent mixture reacts undergoing acid-catalyzed hydrolysis producing acetamide, 59 Da. Further, the highly reactive 43 Da species ethanimine is also produced. These two compounds, normally not observed in APCI analysis, are stabilized by the sulfonamide and appear as adduct species in the mass spectra. The sulfone oxygens and the lone pair of electrons on the amide nitrogen play a role in stabilizing this adduct.     

Rapidly rotating Bose-Einstein condensates in and near the lowest Landau level

We create rapidly rotating Bose-Einstein condensates in the lowest Landau level by spinning up the condensates to rotation rates Omega > 99% of the centrifugal limit for a harmonically trapped gas, while reducing the number of atoms. As a consequence, the chemical potential drops below the cyclotron energy 2 variant Planck's over 2pi Omega. While in this mean-field quantum-Hall regime we still observe an ordered vortex lattice, its elastic shear strength is strongly reduced, as evidenced by the observed very low frequency of Tkachenko modes. Furthermore, the gas approaches the quasi-two-dimensional limit. The associated crossover from interacting- to ideal-gas behavior along the rotation axis results in a shift of the axial breathing mode frequency.     

Observation of Tkachenko oscillations in rapidly rotating Bose-Einstein condensates

We directly image Tkachenko waves in a vortex lattice in a dilute-gas Bose-Einstein condensate. The low (sub-Hz) resonant frequencies are a consequence of the small but nonvanishing elastic shear modulus of the vortex-filled superfluid. The frequencies are measured for rotation rates as high as 98% of the centrifugal limit for the harmonically confined gas. Agreement with a hydrodynamic theory worsens with increasing rotation rate, perhaps due to the increasing fraction of the volume displaced by the vortex cores. We also observe two low-lying m=0 longitudinal modes at about 20 times higher frequency.     

Observation of long-lived vortex aggregates in rapidly rotating Bose-Einstein condensates

We study the formation of large vortex aggregates in a rapidly rotating dilute-gas Bose-Einstein condensate. When we remove atoms from the rotating condensate with a tightly focused, resonant laser, the density can be locally suppressed, while fast circulation of a ring-shaped superflow around the area of suppressed density is maintained. Thus a giant vortex core comprising 7 to 60 phase singularities is formed. The giant core is only metastable, and it will refill with distinguishable single vortices after many rotation cycles. The surprisingly long lifetime of the core can be attributed to the influence of strong Coriolis forces in the condensate. In addition we have been able to follow the precession of off-center giant vortices for more than 20 cycles.