White-light-induced fragmentation of methane

We experimentally probe molecular ionization and dissociation of methane molecules in the gas phase upon their irradiation by intense pulses of white light that spans the wavelength range 500-850 nm. White light pulses are generated upon irradiation of BK7 glass by 36-fs-long pulses of intense 820 nm laser light. Comparison is made of the molecular fragmentation patterns obtained using white light that is depolarized with those obtained using single-color (820 nm) light that is highly chirped. On the basis of such comparison, we make hitherto-unavailable estimates of the in situ intensity of white light pulses. Results obtained using white light also indicate that resonances apparently do not play any role in the ionization dynamics that ensue upon irradiation by intense, broadband light; neither are the dynamics affected by the polarization properties of the 820 nm light that is used to generate the white light.     

3 β ‐Acetoxy‐5 α ‐cholestan‐6‐one: A Steroid

The crystal and molecular structure of 3 β ‐Acetoxy‐5 α ‐cholestan‐6‐one has been determined by X‐ray crystallographic techniques. The compound crystallizes in the space group P2₁ with cell parameters : a = 13.060(3), b=6.299(2), c=17.152(6)Å; β =96.47(3)o, V = 1402.02ų, Z = 2, R = 0.072 for 1921 observed reflections. The six‐membered rings (A, B and C) exist in the chair conformations while the five‐membered ring‐d assumes half‐chair. All rings of the steroid skeleton are trans connected.     

The Twin-Excited State as a Probe for the Transition State in Concerted Unimolecular Reactions: The Semibullvalene Rearrangement

A twin of the transition state , which can be investigated spectroscopically and can thus supply information about the structure of the transition state, has now been characterized for the Cope rearrangement of semibullvalene (shown below). It involves an excited state with B₂ symmetry and results from a linear combination of the ground-state wave functions of (mirror-image) reactant and product.     

Detection and tracking of targets in infrared images using Bayesian techniques

Simple yet robust techniques for detecting targets in infrared (IR) images are an important component of automatic target recognition (ATR) systems. In our previous works, we have developed IR target detection and tracking algorithms based on image correlation and intensity. In this paper, we discuss these algorithms, their performances and problems associated with them and then propose novel algorithms to alleviate these problems. Our proposed target detection and tracking algorithms are based on frequency domain correlation and Bayesian probabilistic techniques, respectively. The proposed algorithms are found to be suitable for real-time detection and tracking of static or moving targets, while accommodating for detrimental affects posed by the clutter and background noise. Finally, limitations of all these algorithms are discussed.     

Simultaneous measurement of proline and related compounds in oak leaves by high-performance ligand-exchange chromatography and electrospray ionization mass spectrometry for environmental stress studies

A mass spectrometer was coupled to high-performance ligand-exchange liquid chromatography (HPLEC) for simultaneous analysis of stress associated solutes such as proline, hydroxyproline, methylproline, glycine betaine and trigonelline extracted from leaves of drought stressed oaks and an internal standard namely N-acetylproline. Methanol/chloroform/water extracts were analyzed using an Aminex HPX-87C column and specifically quantified by the positive ion mode of an electrospray ionisation-mass spectrometry (ESI-MS) in single ion monitoring (SIM) mode. The recovery of N-acetyl proline added to oak leaf extracts ranged from 85.2 to 122.1% for an intra-day study. Standard calibration curves showed good linearity in the measured range from 0.3125 to 10 μmol L⁻¹ with the lowest correlation coefficient of 0.99961 for trigonelline. The advantages of this alternative procedure, compared to previously published methods using fluorescence or amperometric detections, are the simultaneous and direct detection of osmoprotectants in a single chromatographic run, a minimal sample preparation, a good specificity and reduced limits of quantification, ranging from 0.1 to 0.6 μmol L⁻¹. Fifty-six days of water deficit exposure resulted in increased foliar free proline levels (2.4-fold, P < 0.001, 155 μmol g⁻¹ FW) and glycine betaine contents (2.5-fold, P < 0.05, 175 μmol g⁻¹ FW) of drought stressed oak compared to control.     

The Inverted Bond in [1.1.1]Propellane is a Charge‐Shift Bond

Bonded or not bonded? An ab initio valence bond study of [1.1.1]propellane shows that the two bridgehead carbons are linked by a strong and direct σ bond that is neither classically covalent nor classically ionic, but rather a charge‐shift bond, in which the covalent–ionic resonance energy plays the major role. As such, the central bond of [1.1.1]propellane closely resembles the single bond of difluorine.

     

A supercooled imidazolium iodide ionic liquid as a low-viscosity electrolyte for dye-sensitized solar cells

A series of allyl-functionalized imidazolium salts are reported, including 1-allyl-3-ethylimidazolium iodide and 1-allyl-3-propylimidazolium iodide, which have melting points close to room temperature and show typical properties of supercooled fluids if heated above their melting points. Their viscosities in the liquid state are considerably lower than the benchmark ionic liquid used in solar cells, viz., 1-propyl-3-methylimidazolium iodide. Electrolytes containing these new liquids provide excellent efficiencies and good stability in dye-sensitized solar cells when subjected to an accelerated-light soaking test at 60 degrees C. The structures of three of the new salts have been established in the solid state by single-crystal X-ray analysis.     

Identity SN2 reactions X- + CH3X --> XCH3 + X- (X=F, Cl, Br, and I) in vacuum and in aqueous solution: a valence bond study

The recently developed (L. Song, W. Wu, Q. Zhang, S. Shaik, J. Phys. Chem. A 2004, 108, 6017) valence bond method coupled with a polarized continuum model (VBPCM) has been applied to the identity SN2 reaction of halides in the gas phase and in aqueous solution. The barriers computed at the level of the breathing orbital VB method (P. C. Hiberty, J. P. Flament, E. Noizet, Chem. Phys. Lett. 1992, 189, 259), BOVB and VBPCM//BOVB, are comparable to CCSD(T) and CCSD(T)//PCM results and to experimentally derived barriers in solution (W. J. Albery, M. M. Kreevoy, Adv. Phys. Org. Chem. 1978, 16, 85). The reactivity parameters needed to apply the valence bond state correlation diagram (VBSCD) method (S. Shaik, J. Am. Chem. Soc. 1984, 106, 1227), were also determined by VB calculations. It has been shown that the reactivity parameters along with their semiempirical derivations provide a satisfactory qualitative and quantitative account of the barriers.