Improved carrier-envelope phase locking of intense few-cycle laser pulses using above-threshold ionization

A robust nonoptical carrier-envelope phase (CEP) locking feedback loop, which utilizes a measurement of the left-right asymmetry in the above-threshold ionization (ATI) of Xe, is implemented, resulting in a significant improvement over the standard slow-loop f-to-2f technique. This technique utilizes the floating average of a real-time, every-single-shot CEP measurement to stabilize the CEP of few-cycle laser pulses generated by a standard Ti:sapphire chirped-pulse amplified laser system using a hollow-core fiber and chirped mirror compression scheme. With this typical commercially available laser system and the stereographic ATI method, we are able to improve short-term (minutes) CEP stability after a hollow-core fiber from 450 to 290 mrad rms and long-term (hours) stability from 480 to 370 mrad rms.     

Electrochemical Reduction of N2 to NH3 at Low Potential by a Molecular Aluminum Complex

Electrochemical generation of ammonia (NH₃) from nitrogen (N₂) using renewable electricity is a desirable alternative to current NH₃ production methods, which consume roughly 1 % of the world's total energy use. The use of catalysts to manipulate the required electron and proton transfer reactions with low energy input is also a chemical challenge that requires development of fundamental reaction pathways. This work presents an approach to the electrochemical reduction of N₂ into NH₃ using a coordination complex of aluminum(III), which facilitates NH₃ production at −1.16 V vs. SCE. Reactions performed under ¹⁵N₂ liberate ¹⁵NH₃. Electron paramagnetic resonance spectroscopic characterization of a reduced intermediate and investigations of product inhibition, which limit the reaction to sub-stoichiometric, are also presented.     

Development of an on-line sensor for bioreactor operation

Applied Biochemistry and Biotechnology -     

Structure-activity relationships for flow cytometric data of smaller polycyclic aromatic hydrocarbons

Using flow cytometry, select polycyclic aromatic hydrocarbons (PAHs) were evaluated for induction of apoptosis in human monocytic THP-1 cells. Based on structure, the PAHs were divided into linear and bay-region-containing compounds. Except for fluorene, the linear PAHs failed to induce apoptosis; all of the bay-region-containing PAHs induce apoptosis. The relationship that a bay-region is required to induce apoptosis is supported by results for benzo[a]pyrene (positive) and 2-methylanthracene (negative). The data for bay-region containing, four-ringed PAH compounds reveal that possessing a linear-region of more than two rings diminishes the ability of a PAH to induce apoptosis. Owing to the steric interactions of the hydrogen atoms of the methyl group and those on the ring carbons, 1-methylanthracene does not have a true bay-region. However, the methyl group substituted in the 1-position does confer a bay-like conformation, which may explain its activity in contrast to its parent derivative anthracene and its 2-postion homologue.     

Disentangling the volume effect through intensity-difference spectra: application to laser-induced dissociation of H2+

An intensity-difference spectrum method is developed to disentangle the intensity volume effect inherent in focused laser beam interaction with gas-phase matter. This method is applicable to a Gaussian beam of constant axial intensity, which keeps the exact contribution from a predetermined intensity range and eliminates the contributions from lower intensities. We apply this method to the angularly resolved kinetic energy release spectrum of laser-induced dissociation of H2+. The difference spectrum at higher intensities is found to be dominated by the bond-softening process, and the distribution shifts to lower energy and becomes narrower with increasing intensity.     

Development of a differential volume reactor system for soil biodegradation studies

Applied Biochemistry and Biotechnology - A bench scale experimental system was developed for the analysis of polycyclic aromatic hydrocarbon (PAH) degradation by mixed microbial cultures in PAH...     

Delocalization tunable by ligand substitution in [L2Al]n− complexes highlights a mechanism for strong electronic coupling

Ligand-based mixed valent (MV) complexes of Al(iii) incorporating electron donating (ED) and electron withdrawing (EW) substituents on bis(imino)pyridine ligands (I₂P) have been prepared. The MV states containing EW groups are both assigned as Class II/III, and those with ED functional groups are Class III and Class II/III in the (I₂P⁻)(I₂P²⁻)Al and [(I₂P²⁻)(I₂P³⁻)Al]²⁻ charge states, respectively. No abrupt changes in delocalization are observed with ED and EW groups and from this we infer that ligand and metal valence p-orbitals are well-matched in energy and the absence of LMCT and MLCT bands supports the delocalized electronic structures. The MV ligand charge states (I₂P⁻)(I₂P²⁻)Al and [(I₂P²⁻)(I₂P³⁻)Al]²⁻ show intervalence charge transfer (IVCT) transitions in the regions 6850–7740 and 7410–9780 cm⁻¹, respectively. Alkali metal cations in solution had no effect on the IVCT bands of [(I₂P²⁻)(I₂P³⁻)Al]²⁻ complexes containing –PhNMe₂ or –PhF₅ substituents. Minor localization of charge in [(I₂P²⁻)(I₂P³⁻)Al]²⁻ was observed when –PhOMe substituents are included.

Organo-aluminum mixed-valent complexes combine properties of both organic and transition element mixed-valent compounds. This supports delocalized electronic structures that are structurally and electronically tunable.     

Further examples of the failure of surrogates to properly model the structural and hydrothermal chemistry of transuranium elements: insights provided by uranium and neptunium diphosphonates

In situ hydrothermal reduction of Np(VI) to Np(IV) in the presence of methylenediphosphonic acid (C1P2) results in the crystallization of Np[CH2(PO3)2](H2O)2 (NpC1P2-1). Similar reactions have been explored with U(VI) resulting in the isolation of the U(IV) diphosphonate U[CH2(PO3)2](H2O) (UC1P2-1), and the two U(VI) diphosphonates (UO2)2[CH2(PO3)2](H2O)3.H2O (UC1P2-2) and UO2[CH2(PO3H)2](H2O) (UC1P2-3). Single crystal diffraction studies of NpC1P2-1 reveal that it consists of eight-coordinate Np(IV) bound by diphosphonate anions and two coordinating water molecules to create a polar three-dimensional framework structure wherein the water molecules reside in channels. The structure of UC1P2-1 is similar to that of NpC1P2-1 in that it also adopts a three-dimensional structure. However, the U(IV) centers are seven-coordinate with only a single bound water molecule. UC1P2-2 and UC1P2-3 both contain U(VI). Nevertheless, their structures are quite distinct with UC1P2-2 being composed of corrugated layers containing UO 6 and UO 7 units bridged by C1P2; whereas, UC1P2-3 is found as a polar three-dimensional network structure containing only pentagonal bipyramidal U(VI). Fluorescence measurements on UC1P2-2 and UC1P2-3 exhibit emission from the uranyl moieties with classical vibronic fine-structure.     

Molecular site assessment and process monitoring in bioremediation and natural attenuation

A variety of modern biotechnical approaches are available to assist in optimizing and controlling bioremediation processes. These approaches are broad-ranging, and may include genetic engineering to improve biodegradative performance, maintenance of the environment, and process monitoring and control. In addition to direct genetic engineering strategies, molecular diagnostic and monitoring technology using DNA gene probing methods and new quantitative mRNA analytical procedures allows direct analysis of degradative capacity, activity, and response underin situ conditions. Applications of these molecular approaches in process developments for trichloroethylene (TCE), polychlorinated biphenyls (PCB), and polynuclear aromatic hydrocarbons (PAH) bio-oxidation in soils, aquifer sediments, and ground-water treatment reactors have been demonstrated. Molecular genetic technologies permit not only the development of new processes for bioremediation, but also new process monitoring, control strategies, and molecular optimization paradigms that take full advantage of vast and diverse abilities of microorganisms to destroy problem chemicals.     

Dissociation and ionization of H+2 by ultrashort intense laser pulses probed by coincidence 3D momentum imaging

Laser-induced dissociation and ionization of H(+)(2) were simultaneously measured using coincidence 3D momentum imaging, allowing direct separation of the two processes, even where the fragment kinetic energy is the same for both processes. The results for 45 and 135 fs 790 nm pulses with an intensity of approximately 2.5 x 10(14) W/cm(2) differ from each other much more than one would expect from previous measurements with longer pulses. Ionization was negligible for the longer pulse and was strongly aligned along the laser polarization for the shorter pulse, but showed no structure in its kinetic energy distribution. In addition, the ionization to dissociation ratio was found to be much smaller than theoretically predicted for H(+)(2).