Energy transfer in collisional activation of gaseous organic ions

The amounts of translational energy lost in the collisional activation (CA) of CH₄⁺, CD₄⁺, CH₃⁺, and CD₃⁺ to form the possible C(H,D)_0–3⁺ products have been measured. These values are consistent with the gain in internal energy required to produce the observed decomposition in unimolecular reactions, as predicted by the quasi-equilibrium theory. Further, there appear to be marked differences in the distribution of internal energy values of CH₄⁺ produced by electron ionization of CH₄ and the distribution produced by CA of low energy CH₄⁺ ions.     

Laser separation of oxygen isotopes by IR multiphoton dissociation of (CH3)2O

Isotopically selective (with respect to ¹⁸O) one- and two-frequency multiphoton dissociation of dimethyl ether (CH₃)₂O by pulsed TEA CO₂ laser radiation has been studied. The maximum primary selectivity, 16, is attained with the dissociation yields of the desired component (CH₃) ₂ ¹⁸ O ₁₈=5×10^–4 and 1.7×10^–2 for one- and two-frequency excitation, respectively. The dependences of MPD yields and selectivity on laser radiation frequency, (CH₃)₂O pressure, buffer gas (N₂) pressure and temperature have been measured. Multiphoton absorption coefficients have been measured and the average number of absorbed quanta calculated. The laser photon energy consumed for separating one ¹⁸O atom has been estimated: 11 and 4 keV/¹⁸O atom for one- and two-frequency excitation, respectively.     

On accounting for the effect of particles of a condensed dispersed phase on radiant energy transfer in gaseous media

Questions concerning the formation of the optical properties of dense gaseous and plasma media in relation to the specific features of radiant energy transfer are considered. The integral equations describing the radiation trapping are investigated as a new class of generalized wave equations of Schrödinger type. Starting from the methods of quantum mechanics, original analytical and numerical approaches are suggested for solving problems of the radiative kinetics of both spatially homogeneous and inhomogeneous absorbing media containing dispersed particles. In terms of the quasi-classical approximation, two classes of reference problems for determination of phase factors are formulated. Solutions for a number of model problems are presented that demonstrate the efficiency of the methods developed.     

Binding of Mn(II) ions to lecithin bilayers as determined by ESR and NMR investigations

Summary The Mn(II)-lecithin system was investigated by means of paramagnetic relaxation studies. Unsonicated and sonicated aqueous dispersions were considered at various temperatures andpH values. Information was derived from both the frequency dependence of the ESR line shape and the paramagnetic contributions to the water proton relaxation rates. A dynamic equilibrium was suggested, by taking into account the role of the through-water cation binding in the metal-lipid interaction.

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Riassunto Il sistema Mn(II)-lecitina è stato studiato per mezzo di misure di rilassamento paramagnetico. Sono state considerate dispersioni acquose sonicate e non a vari valori di temperature epH. Da misure EPR in funzione della frequenza e dallo studio di contributi paramagnetici alle velocità di rilassamento dei protoni dell’acqua sono state ottenute informazioni sul sistema Mn(II)-lecitina. Prendendo in considerazione il ruolo del legame acqua-catione, nell’interazione metallo lipide, è stato suggerito un equilibrio dinamico.

     

Study of the sputtering of adsorbates by low energy ions (O on Ni)

Sputtering or ion impact desorption of adsorbed layers has been studied by low energy ion scattering and model calculations. For adsorption of a monolayer or less (e.g. oxygen on nickel) the desorption by ions can be readily observed by He⁺ ion scattering from the development of the adsorbate and substrate signal as a function of time. Desorption cross sections for Ne⁺ and He⁺ ions in the energy range from 500 eV to 1600 eV are given. These results are compared with the model calculations and the influence of various parameters can be studied by this comparison. The contribution of different processes to the sputtering mechanism is discussed.     

Characterization of a broadband pulse for phase controlled multiphoton microscopy by single beam SPIDER

We present what we believe to be a new version of spectral phase interferometry for direct electric field reconstruction (SPIDER) using only a single-phase and polarization controlled laser beam. Two narrow pulses and one broadband pulse are selected out of an ultrafast laser pulse by a polarization and phase control technique to generate second harmonic generation (SHG) signals, which are equivalent to a spectral shear interferogram in the conventional SPIDER method. The spectral phase of the broadband laser pulse is extracted analytically with double quadrature spectral interferometry (DQSI). An arbitrary spectral phase can be retrieved with great precision and compensated in situ at the sample position of a microscope. This new method requires no separate reference beam and is suitable for nonlinear optical microscopy with a phase controlled laser pulse.     

A numerical study of energy transfer mechanisms in materials following irradiation by swift heavy ions

Swift heavy ions interact with electrons in materials and this may yield permanent atomic displacements; the energy transfer mechanisms that bring electronic excitations into atomic motion are not fully understood, and are generally discussed in terms of two theories, viz. Coulomb explosion and heat exchange between excited electrons and atoms, which is limited by electron-phonon coupling. We address this problem for a “generic” material using a semi-classical numerical approach where the dynamics of the evolving electron density is calculated by using molecular dynamics simulations applied to pseudo-electrons. The forces exerted on the nuclei are then used to calculated the trajectories of the nuclei. From the temporal evolution of the atomic kinetic energy, we find that the energy transfer between the electrons and the nuclei can be divided in two parts. First, a Coulomb heating starts the motion of the atoms by giving them a radial speed; this process differs from Coulomb explosion because the atoms are not displaced over interatomic distances. Second, a thermal energy transfer, as described in linear transport theory, takes place. Our study thus confirms the domination of thermal energy exchange mechanisms over Coulomb explosion models.     

Investigations of multiphoton selective dissociation of (CH3)2O in the field of a pulsed CO2 laser

Experimental investigations of multiphoton selective dissociation of (CH₃)₂O induced by a pulsed CO₂ laser have been conducted. Separation of H, C, and O isotopes was performed in enriched mixtures and in samples with the natural abundance. The following coefficients of selectivity have been obtained:K _D/K_H=4.0,K ₁₃/K₁₂=1.7, andK ₁₈/K₁₆≧1.6. We studied the dependences of the selectivity coefficient on ether pressure, on the laser energy and frequency as well as the influence of secondary chemical reactions on the dissociation selectivity. Estimations made by using the RRKM theory have indicated that ether molecules that decompose have an average excitation energy above the dissociation threshold of ∼1.5 kcal/mole.     

Influence of the potential energy surface on the cross sections for deeply inelastic transfer reactions induced by heavy ions

Large differences are observed in the cross sections for deeply inelastic reactions involving the transfer of several charges from ⁴⁰Ca and ⁴⁰Ar projectiles to the same rare-earth targets. The cross sections for four and six charge transfers from projectile to target are enhanced for ⁴⁰Ca incident ions. These differences are qualitatively explained by considering that the drift paths in the (Z, A) plane are governed by a static potential energy surface which describes the composite system. Shell corrections have been included in the calculation of this potential energy surface.     

Strong dependence of ir multiphoton absorption and dissociation yield of SF6 molecule on intensity (duration) of exciting laser pulse

The role of played by the intensity of the exciting TEA CO₂ laser pulses in the processes of ir multiphoton absorption (MPA) of SF₆ molecules cooled toT _R?40 K andT _v?160 K in a pulsed supersonic jet and the dissociation of SF₆ in a bulk atT?300 K under essentially collisionless conditions have been investigated. A strong dependence of MPA and the dissociation yield on pulse intensity were observed. The frequency dependences of the intensity effects were studied.     

Improved anti-Stokes energy transfer between rare earth ions in Er（0.5）Yb（9.5）：FOV oxyfluoride vitroceramics explains the strong color reversal

The widely used energy transfer theory is a foundation of luminescence,in which the rates of Stokes and antiStokes processes have the same calculation formula.An improvement on the anti-Stokes energy transfer to explain the fluorescence intensity reversal between the red and green fluorescence of Er(0.5)Yb(9.5):FOV is reported in the present article.The range of the intensity reversal Σ was measured to be 877.Dynamic processes for 16 levels were simulated.A coefficient,the improvement factor of the intensity ratio of Stokes to anti-Stokes processes in quantum Raman theory compared to classical Raman theory,is introduced to successfully describe the anti-Stokes energy transfer.A new method to calculate the distance between the rare earth ions,which is critical for the energy transfer calculation,is proposed.The validity of these important improvements is also proved by experiment.     

Identification of glucosinolates in capers by LC-ESI-hybrid linear ion trap with Fourier transform ion cyclotron resonance mass spectrometry (LC-ESI-LTQ-FTICR MS) and infrared multiphoton dissociation

An liquid chromatography-mass spectrometry method using electrospray ionization in negative ion mode coupled with a hybrid quadrupole linear ion trap and Fourier transform ion cyclotron resonance (FTICR) mass spectrometer was applied to characterize of intact glucosinolates (GLSs) in crude sample extracts of wild bud flowers of Capparis spinosa (Capparis species, family Capparaceae). Structural information of GLSs was obtained upon precursor ions' isolation within the FTICR trapping cell and subsequent fragmentation induced by infrared multiphoton dissociation (IRMPD). Such a fragmentation was found very useful in terms of chemical identification of all precursor ions [M-H](-) including sulfur-rich GLSs reported here for the first time. Along with most common GLSs already found in capers such as glucocapparin, isopropyl/n-propyl-GLS, mercapto-glucocapparin, and two indolic GLS, i.e., 4-hydroxyglucobrassicin and glucobrassicin, the occurrence of the uncommon glycinyl-glucocapparin as well as two sulfur-rich GLSs is reported. IRMPD showed an increased selectivity towards disulfide bond cleavages with thiol migration, suggesting the side chain structure of non-targeted compounds, i.e., disulfanyl-glucocapparin and trisulfanyl-glucocapparin. Glucocapparin [2.05?±?0.25?mg/g, dry weight (dw)] was the most abundant GLS, followed by glucobrassicin (232?±?18?μg/g, dw) and 4-hydroxyglucobrassicin (89?±?12?μg/g, dw). All other compounds were present at very low content ranging from 0.5 to 1.5?μg/g dw. Copyright ? 2012 John Wiley & Sons, Ltd.     

Computer simulation of an energy transfer dye laser (ETDL)

Computer calculations of an energy transfer dye laser (ETDL) performance are presented. It is shown that the ETDL output can be manipulated by varying the donor or acceptor concentrations. Experiments done on the anthracene-perylene ETDL are in agreement with the predictions of the present calculation.     

Calculation of anharmonic effects in the unimolecular dissociation of M2+(H2O)2 (M = Be,Mg, and Ca)

The anharmonic and harmonic rate constants of the unimolecular dissociation of M²⁺(H₂O)₂ (M = Be, Mg, and Ca) were calculated using the Rice–Ramsperger–Kassel–Marcus theory. The anharmonic effects of the reactions were investigated. The results show that the energy barrier of the dissociation of Be²⁺(H₂O)₂ is 68.47 kcal/mol, and the anharmonic (T_4000K = 4.28×10⁸ s^?1) and harmonic (T_4000K = 4.22×10⁸ s^?1) rate constants were close in value in both the canonical and microcanonical systems. The energy barriers of the two steps for the dissociation, Mg²⁺(H₂O)₂ → MgOH⁺+H₃O⁺, were 37.41 and 11.39 kcal/mol, and those for the dissociation, Ca²⁺(H₂O)₂ → CaOH⁺+H₃O⁺, were 21.15 and 26.42 kcal/mol. The anharmonic effect of the two reactions is significant and cannot be neglected in both the canonical and microcanonical systems. The comparison also shows that the rate constants of the dissociation of Ca²⁺(H₂O)₂ have the maximum values, while those of Be²⁺(H₂O)₂ have the minimum values in the three reactions; however, the anharmonic effect also shows the similar trend in the comparison.     

Enhanced luminescence of rare-earthTb (III) by Tm (III) in bis(benzoylmethyl) sulfoxide complexes and intra-molecular energy transfer

Rare-earth complexes [(Tb_xTm_y)L₅(ClO₄)₂](ClO₄)·3H₂O(x:y=1.000:0.000, 0.999:0.001, 0.995:0.005, 0.990:0.010, 0.950:0.050, 0.900:0.100, 0.800:0.200, 0.700:0.300; L=C₆H₅COCH₂SOCH₂COC₆H₅) were synthesized and characterized with elemental analysis, infrared spectra (IR) and ¹H NMR. The photophysical properties of these complexes were studied in detail with ultraviolet absorption spectra, fluorescent spectra and lifetimes. The fluorescence spectra and decay curves of complexes indicated that the fluorescence emission intensity was enhanced and the fluorescence lifetime was prolonged by Tm (III), which may be due to the intra-molecular energy transfer between inert rare-earth ions and active rare-earth ions. The complexes showed the best properties when the mole ratio of Tb (III) to Tm (III) is 0.995:0.005. The intensity of fluorescence can be increased to 208%. Additionally, the energy-transfer mechanisms between the ligand and the central Tb (III) ions were discussed.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Elasticity of polymer solutions in Couette flow measured by fluorescence resonance energy transfer (FRET)

Polymer solutions are complex fluids that show elasticity and deformation in response to shear flows. A fluorescence resonance energy transfer (FRET) technique has been applied to measure the end-to-end distances of individual polymer molecules in Couette flow, using end-tagged reversible-addition fragmentation chain transfer (RAFT) polymerised poly(methyl methacrylate) (PMMA). Real-time rheofluorescence measurements on these polymers in solution above the critical overlap concentration are reported at several shear rates. The PMMA in Couette flow shows a systematic decrease in fluorescence, corresponding to a reduction in end-to-end distance of the polymer molecules with shear exposure. Full reversibility of the fluorescence signal is observed after the cessation of shear. These results show that polymer solution elasticity arises from compressive deformation of the polymer molecules in Couette flow. At polymer concentrations above the critical overlap, the polymer molecules are restricted by their neighbours and the net hydrodynamic forces are compressive rather than extensive.