Mass analyzed threshold ionization spectra of phenol...Ar2: ionization energy and cation intermolecular vibrational frequencies

The phenol(+)...Ar(2) complex has been characterized in a supersonic jet by mass analyzed threshold ionization (MATI) spectroscopy via different intermediate intermolecular vibrational states of the first electronically excited state (S(1)). From the spectra recorded via the S(1)0(0) origin and the S(1)β(x) intermolecular vibrational state, the ionization energy (IE) has been determined as 68,288 ± 5 cm(-1), displaying a red shift of 340 cm(-1) from the IE of the phenol(+) monomer. Well-resolved, nearly harmonic vibrational progressions with a fundamental frequency of 10 cm(-1) have been observed in the ion ground state (D(0)) and assigned to the symmetric van der Waals (vdW) bending mode, β(x), along the x axis containing the C-O bond. MATI spectra recorded via the S(1) state involving other higher-lying intermolecular vibrational states (σ(s)(1), β(x)(3), σ(s)(1)β(x)(1), σ(s)(1)β(x)(2)) are characterized by unresolved broad structures.     

Approximate factoring of the inverse

Computation of approximate factors for the inverse constitutes an algebraic approach to preconditioning large and sparse linear systems. In this paper, the aim is to combine standard preconditioning ideas with sparse approximate inverse approximation, to have dense approximate inverse approximations (implicitly). For optimality, the approximate factoring problem is associated with a minimization problem involving two matrix subspaces. This task can be converted into an eigenvalue problem for a Hermitian positive semidefinite operator whose smallest eigenpairs are of interest. Because of storage and complexity constraints, the power method appears to be the only admissible algorithm for devising sparse–sparse iterations. The subtle issue of choosing the matrix subspaces is addressed. Numerical experiments are presented.     

Frequency-comb-referenced molecular spectroscopy in the mid-infrared region

A simple method for absolute-frequency measurements of molecular transitions in the mid-IR region is reported. The method is based on a cw singly resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45?μm. The mid-IR frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute-frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated.     

Surface initiated polymerization of a cationic monomer on inner surfaces of silica capillaries: Analyte separation by capillary electrophoresis versus polyelectrolyte behavior

[2‐(Methacryloyl)oxyethyl]trimethylammonium chloride was successfully polymerized by surface‐initiated atom transfer radical polymerization method on the inner surface of fused‐silica capillaries resulting in a covalently bound poly([2‐(methacryloyl)oxyethyl]trimethylammonium chloride) coating. The coated capillaries provided in capillary electrophoresis an excellent run‐to‐run repeatability, capillary‐to‐capillary and day‐to‐day reproducibility. The capillaries worked reliably over 1 month with EOF repeatability below 0.5%. The positively charged coated capillaries were successfully applied to the capillary electrophoretic separation of three standard proteins and five β‐blockers with the separation efficiencies ranging from 132 000 to 303 000 plates/m, and from 82 000 to 189 000 plates/m, respectively. In addition, challenging high‐ and low‐density lipoprotein particles could be separated. The hydrodynamic sizes of free polymer chains in buffers used in the capillary electrophoretic experiments were measured for the characterization of the coatings.     

Low-loss photon-to-electron conversion

Silicon photodiodes with induced junction structure can reach low-loss photon-to-electron conversion. The calculated conversion efficiency in the visible wavelength range typically deviates less than 10 ppm from unity and its uncertainty is about 100 ppm at room temperature or as low as 1 ppm at 78 K. Here we show experimentally that our dedicated induced junction photodiodes indeed have very low conversion losses when they are assembled in a light trapping structure as provided by, for example, the predictable quantum efficient detector (PQED). It is concluded that the remaining measured losses, if any, are probably due to surface recombination of electrons and holes close to the silicon/silicon dioxide interface of the photodiode.     

Molecular Engineering of Fracture Energy Dissipating Sacrificial Bonds Into Cellulose Nanocrystal Nanocomposites

Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one‐component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2‐ureido‐4[1H]‐pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites.     

Stereoselective total synthesis of pachastrissamine (jaspine B)

A short total synthesis of the cytotoxic natural product pachastrissamine is described. The synthesis includes eight steps starting from Garner’s aldehyde and proceeds in 20% overall yield. Pd(0)-mediated intramolecular cyclisation and Ru-mediated cross-metathesis are the key reactions in this sequence.     

N−X⋅⋅⋅O−N Halogen Bonds in Complexes of N-Haloimides and Pyridine-N-oxides: A Large Data Set Study

N−X⋅⋅⋅⁻O−N⁺ halogen-bonded systems formed by 27 pyridine N-oxides (PyNOs) as halogen-bond (XB) acceptors and two N-halosuccinimides, two N-halophthalimides, and two N-halosaccharins as XB donors are studied in silico, in solution, and in the solid state. This large set of data (132 DFT optimized structures, 75 crystal structures, and 168 ¹H NMR titrations) provides a unique view to structural and bonding properties. In the computational part, a simple electrostatic model (SiElMo) for predicting XB energies using only the properties of halogen donors and oxygen acceptors is developed. The SiElMo energies are in perfect accord with energies calculated from XB complexes optimized with two high-level DFT approaches. Data from in silico bond energies and single-crystal X-ray structures correlate; however, data from solution do not. The polydentate bonding characteristic of the PyNOs’ oxygen atom in solution, as revealed by solid-state structures, is attributed to the lack of correlation between DFT/solid-state and solution data. XB strength is only slightly affected by the PyNO oxygen properties [(atomic charge (Q), ionization energy (I_s,min) and local negative minima (V_s,min)], as the σ-hole (V_s,max) of the donor halogen is the key determinant leading to the sequence N-halosaccharin>N-halosuccinimide>N-halophthalimide on the XB strength.     

Structural Characteristics of Hydrogenated Carbon and Boron Nitride Nanotubes: Impact of H?H Interactions

The structural characteristics of perhydrogenated carbon and boron nitride nanotubes are determined by means of quantum chemical calculations. Two families of nanotubes are systematically studied for both carbon and boron nitride, the nanotubes being derived from the perhydrogenated (110) and (111) sheets of diamond and cubic boron nitride. Single‐walled perhydrogenated carbon nanotubes prefer structures analogous to the (111) sheet. In clear contrast, the single‐walled perhydrogenated boron nitride nanotubes prefer structures analogous to the (110) sheet. The significantly different structural characteristics are due to the polarization of hydrogen atoms in the perhydrogenated boron nitride nanotubes. The presence of attractive electrostatic H? H interactions leads to a strong preference for multilayering of the boron nitride sheets and nanotubes. The results are expected to provide new insights into the structural characteristics of main‐group binary hydrides.     

Detailed analysis of the cation ground state of three dichlorobenzenes by mass analyzed threshold ionization spectroscopy

Two color resonant mass analyzed threshold ionization (MATI) spectroscopy was applied in order to investigate the ionic properties of the structural isomers of dichlorobenzene above the ionization threshold. A detailed analysis of the vibrational properties of the two main chlorine isotopomers of each isomer was performed resulting in a precise picture of the vibrational states in the cation ground states. The general features of the two investigated isotopomers turned out to be quite similar, although some vibrational modes are slightly different up to a few wavenumbers, except for the 6b normal mode of p-dichlorobenzene. There the spectrum of the (35)Cl(2)-isotopomer shows several additional peaks compared to the one of the (35)Cl(37)Cl-isotopomer. An explanation for the extraordinary observance is discussed. In addition to the examination of the ionic ground state the measured and calculated frequencies were used to confirm the former assignment of the vibrations in the S(1) state, especially with respect to a Herzberg-Teller coupling as observed in benzene.