LIF technique offers the potential for the detection of cadmium-induced alteration in photosynthetic activities of Zea Mays L.

The laser-induced fluorescence spectra of leaves of Zea mays L. plants treated with different concentrations (0.01, 0.10 and 1.00 mM) of cadmium were recorded in region 650–800 nm using 488 nm line of Argon Ion laser as excitation source and PMT as detector. Besides this, blue-green fluorescence and Chl fluorescence were also measured using third harmonic (355 nm) of Nd:YAG laser as excitation source and 320 M monochromator with intensified charge coupled device as a detector in the region 400–800 nm. These spectra have been used to analyse the effect of several doses of cadmium on the photosynthetic activities of Z. mays L. plants. The fluorescence intensity ratios (FIR) of control as well as treated Z. mays L. were calculated by evaluating curve-fitted parameters using Gaussian spectral function. In addition, growth parameters like photosynthetic pigments content were also estimated. The chlorophyll fluorescence intensity ratio F685/F735 excited by both 488 and 355 nm lines are strongly correlated with photosynthetic pigments content (total chlorophyll and carotenoids) and their ratios. Consequently, there also existed a correlation between the blue-green fluorescence intensity ratio F470/F540 and photosynthetic pigments content.     

Free NH3 quantum rotations in Hofmann clathrates: structure factors and line widths studied by inelastic neutron scattering

Quantum rotations of NH₃ groups in Hofmann clathrates Ni–Ni–C₆H₆ and Ni–Ni–C₁₂H₁₀ have been studied using inelastic neutron scattering. Calculations of the dynamical structure factor for a free uniaxial quantum rotor reproduce the neutron scattering data with respect to their Q- and T-dependence as well as the relative intensities for the 0 → 1, 0 → 2 and 1 → 2 transitions. Though the effective NH₃ rotation constant is different from the gas phase value, the effective radius of rotation (i.e., the average distance of protons from the rotation axis) is equal or very close to the geometrical value r = 0.94 Å for a NH₃ group. Comparing the experimental data with the calculated dynamical structure factor for the 0 → 3 transition it could be shown, that the corresponding transition line, in contrast to transitions between j = 0,1,2 levels measured so far, has a finite width at T = 0 K.     

Radiative transport and collisional transfer of excitation energy in Cs vapors mixed with Ar or He

This paper is a review (with a few original additions) on the radiative transport and collisional transfer of energy in laser-excited cesium vapors in the presence of argon or helium. Narrow-band excitation of lines with Lorentz, Doppler and Voigt profiles is studied in order to calculate effective rates for pumping of spectral lines with profiles comprising inhomogeneous broadening components. The radiative transport of excitation energy is considered, and a new, simple and robust, but accurate theoretical method for quantitative treatment of radiation trapping in relatively optically thin media is presented. Furthermore, comprehensive lists of experimental values for the excitation energy transfer cross-sections related to thermal collisions in Cs–Ar and Cs–He mixtures are given. Within the collected cross-section data sets, specific regularities with respect to the energy defect, as well as the temperature, are discerned. A particular emphasis is put on the radiative and collisional processes important for the optimization of resonance–fluorescence imaging atomic filters based on Cs–noble gas systems.     

Optical and dielectric properties of isothermally crystallized nano-KNbO3 in Er3+-doped K2O–Nb2O5–SiO2 glasses

Precursor glass of composition 25K₂O–25Nb₂O₅–50SiO₂ (mol%) doped with Er₂O₃ (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO₃ nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO₃ estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO₃ phase. The measured visible photoluminescence spectra have exhibited green emission transitions of ²H_11/2, ⁴S_3/2 → ⁴I_15/2 upon excitation at 377 nm (⁴I_15/2 → ⁴G_11/2) absorption band of Er³⁺ ions. The near infrared (NIR) emission transition ⁴I_13/2 → ⁴I_15/2 is detected around 1550 nm on excitation at 980 nm (⁴I_15/2 → ⁴I_11/2) of absorption bands of Er³⁺ ions. It is observed that photoluminescent intensity at 526 nm (²H_11/2 → ⁴I_15/2), 550 nm (⁴S_3/2 → ⁴I_15/2) and 1550 nm (⁴I_13/2 → ⁴I_15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (τ_f) of the ⁴I_13/2 → ⁴I_15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er³⁺ ions gradually enter into the KNbO₃ nanocrystals.     

Application of a laser produced plasma: Experimental Stark widths of single ionized lead lines

The optical emission spectroscopy from laser produced plasma generated by a 10,640 Å radiation, with an irradiance of 1.4 × 10¹⁰ W cm^− 2 on several lead targets, in vacuum and in an atmosphere of argon, was recorded and analyzed between 1900 and 7000 Å. The Local Thermodynamic Equilibrium conditions and plasma homogeneity have been checked. Stark widths for 31 lines of Pb II have been measured. These lines measured in this work correspond to the transitions 7s → 6p, n(n = 8, 9, 10)s → 7p, n(n = 7, 8)p → 7s, n(n = 7, 8)p → 6p², n(n = 7, 8)d → 7p, n(n = 5, 6)f → 6d, n(n = 5, 6)f → 6p². The population level distribution and the corresponding temperatures were obtained using Boltzmann plots. The plasma electron densities were determined using well-known Stark broadening parameters of spectral lines. Special attention was dedicated to the possible self-absorption of the different transitions. Temporal evolution of the plasma parameters was studied between 0.1 and 9 μs. Stark broadening parameters of the spectral lines were measured at 2.5 μs where the electron temperature was close to 11,300 K and the electron density to 0.8 × 10¹⁶ cm^− 3. The experimental results obtained have been compared with the experimental and theoretical values given by other authors. A systematic trend of this parameter versus temperature of 4244.9 Å Pb II line has been presented.     

Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies

The light-induced spin and structure changes upon excitation of the singlet metal-to-ligand charge transfer (¹MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([Fe^II(bpy)₃]²⁺) by a combination of ultrafast optical and X-ray spectroscopies. Polychromatic femtosecond fluorescence up-conversion, transient absorption studies in the 290–600 nm region and femtosecond X-ray absorption spectroscopy allow us to retrieve the entire photocycle upon excitation of the ¹MLCT state from the singlet low-spin ground state (¹GS) as the following sequence: ^1,3MLCT → ⁵T → ¹GS, which does not involve intermediate singlet and triplet ligand-field states. The population time of the HS state is found to be ～150 fs, leaving it in a vibrationally hot state that relaxes in 2–3 ps, before decaying to the ground state in 650 ps. We also determine the structure of the high-spin quintet excited state by picosecond X-ray absorption spectroscopy at the K-edge of Fe. We argue that given the many common electronic (ordering of electronic states) and structural (Fe–N bond elongation in the high-spin state, Fe–N mode frequencies, etc.) similarities between all Fe(II)-polypyridine complexes, the results on the electronic relaxation processes reported in the case of [Fe^II(bpy)₃]²⁺ are of general validity to the entire family of Fe(II)-polypyridine complexes.     

A time-dependent wave packet study of the H4 four-center reaction

A quantum model based on the time-dependent initial state selected wave packet approach was developed to study the four-center (4C) reaction, A₂ + B₂ → 2AB, and the competing collision induced dissociation (CID), A₂ + B₂ → A + B₂ + A, as applied to the H₂(v₁) + H₂(v₂) system important in combustion. A reduced three-dimensional model of the reaction with the atoms constrained to an isosceles trapezium and a realistic global potential energy surface of Aguado et al. [J. Chem. Phys. 101 (1994) 2742], following Hernández and Clary [J. Chem. Phys. 104 (1996) 8413], was used. A method to analyse the reaction flux for 4C and CID reaction probabilities is presented. The initial A₂ vibrational excitation is not only more efficient than translational energy in facilitating the 4C and CID processes, it also reduces the threshold energy. Both the 4C and CID processes exhibit similar threshold energy behavior. For low vibrational excitation in the A₂ diatom, the 4C process is dominant; as the A₂ diatom becomes highly excited the CID process becomes more important at low collision energies with B₂, but as the collision energy increases the 4C process is favored again.     

Nano Au enhanced upconversion in dichroic Nd3+:Au–antimony glass nanocomposites

Dichroic Nd³⁺:Au–antimony glass (K₂O–B₂O₃–Sb₂O₃) nanocomposites (NCs) have been synthesized by single-step melt-quench thermochemical reduction process. The UV–Vis–NIR spectra show surface plasmon resonance (SPR) band of Au⁰ nanoparticles (NPs) and absorption peaks of Nd³⁺ ions. XRD and SAED results indicate growth of Au⁰ NPs along (200) plane. TEM image reveals elliptical Au⁰ NPs having sizes 12–21 nm (aspect ratio ～1.2) responsible for the dichroic behavior. Photoluminescent upconversion under excitation at 805 nm exhibit two emission bands of Nd³⁺ ions at 540 (green) and 650 (red) nm due to ⁴G_7/2 → ⁴I_9/2 and ⁴G_7/2 → ⁴I_13/2 transitions respectively. Both bands undergo maximum 8 and 11 fold intensity enhancements respectively at 0.03 wt% Au⁰ (4.1 × 10¹⁸ atoms/cm³). Local field enhancement (LFE) induced by Au⁰ SPR and energy transfer (ET) from Au⁰ → Nd³⁺ is found to be responsible for enhancement while ET from Nd³⁺ → Au⁰ and optical re-absorption due to Au⁰ SPR for quenching.     

Recognition of DNA based on changes in the fluorescence intensity of CdSe/CD QDs–phenanthroline systems

The CdSe quantum dots (QDs) modified by mercapto-β-cyclodextrin (CD) were synthesized and characterized by transmission electron microscopy, powder X-ray diffraction, excitation and emission spectra, and fluorescence lifetime. When λ_ex = 370 nm, the fluorescence peak of CdSe/CD QDs is at 525 nm. Phenanthroline (Phen) is able to quench their fluorescence, which can be recovered by the addition of DNA. The quenching and restoration of fluorescence intensity were found to be linearly proportional to the amount of Phen and DNA, respectively. The variation of the fluorescence intensity of the CdSe/CD QDs–Phen system was studied, and it was demonstrated to result from a static mechanism due to the formation of a Phen inclusion complex with the CdSe QDs modified by mercapto-β-cyclodextrin. The fluorescence recovery was due to the binding of DNA with Phen in the inclusion complex, leading to the freeing of the CdSe/CD QDs. The binding constants and sizes of the binding sites of the Phen–DNA interaction were calculated to be 1.33 × 10⁷ mol^?1 L and 10.79 bp.     

Excited state structural dynamics and Herzberg–Teller coupling of tetraphenylporphine explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman spectra of free-base tetraphenylporphine (TPP) were obtained with 397.9, 416, and 435.7 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the resonance Raman spectra (RRs) of TPP. The RRs indicate that the Franck–Condon region photodynamics for S₀ → S₄ electronic state is predominantly along the C_m–ph stretch while that for S₀ → S₃ electronic state is predominantly along the porphin ring C_βC_β stretch. Non-totally symmetric vibrational modes were regularly presented in resonance Raman spectra: the shorter the excitation wavelengths were, the stronger intensity the modes had, which can be interpreted in terms of electric dipole transition moments caused by Franck–Condon and Herzberg–Teller coupling.Four non-total symmetry vibrational mode υ_52, υ₆₄, υ₉₇ and υ₁₃₀ in A₂ irreducible representative of TPP were observed in 397.9, 416 and 435.7 nm resonance Raman spectrum. With the shorter wavelength laser excitations at 416 or 397.9 nm, the A₂ vibrational modes show more enhanced Raman intensity by comparison with those in the TPP spectrum excited at 435.7 nm.     

Photolysis of glyoxal in air

The photolysis of glyoxal in synthetic air was investigated in a quartz cell at 298 K using three types of UV sources (TL/12 lamps (275–380 nm), TL/03 lamps (390–470 nm) and mercury lamps (254 nm)) and products were identified and quantitatively analyzed using long-path FTIR spectroscopy. For all light sources, the observed products were CO, HCHO and HCOOH. Absolute quantum yields were determined using Cl₂ and Br₂ as actinometers. Photolysis in the first absorption band of glyoxal, using TL/12 lamps, provided an overall quantum yield of Φ_T = 0.97 ± 0.05, independent of total pressure ranging from 100 to 700 Torr air. The absolute quantum yields obtained with the TL/03 lamps, covering the second absorption band of glyoxal, showed dependency on total pressure, ranging from Φ_T = 0.12 at 100 Torr to Φ_T = 0.042 at 700 Torr, which can be expressed as a Stern–Volmer-type equation 1/Φ_T = (6.80 + 251.8) × 10⁻⁴ × P (Torr).By combining the product yields with literature data, we deduced the detailed picture of glyoxal photolysis, including the dependency of the quantum yield of each particular channel: CHOCHO + hν → 2HCO (Φ₁); CHOCHO + hν → H₂ + 2CO (Φ₂); CHOCHO + hν → H₂CO + CO (Φ₃) on the applied wavelength. The product quantum yields indicate that dissociation into two HCO radicals is the most important pathway under atmospheric conditions. The mean photolysis rate was measured under solar radiation in the EUPHORE outdoor chamber to be J_obs = 1.04 ± 0.10 × 10⁻⁴ s⁻¹, corresponding to a mean effective quantum yield ϕ_eff = 0.035 ± 0.007. Although glyoxal has a very low effective quantum yield, photolysis remains an important removal path in the atmosphere.     

Slab calculations and Green’s function recursive methods combined to study the electronic structure of surfaces: application to Cu(1 1 1)–(4 × 4)-Na

We have recently developed an ab initio scheme for the calculation of the electronic structure of surfaces. The method is based on the combination of density functional calculations using finite slabs and the use of recursive methods to obtain the Green’s function of the surface. The slab calculations are performed using a linear combination of atomic orbitals as a basis set. From such calculation we directly obtain the surface Hamiltonian in a tight-binding form. Combining this information with that from a bulk calculation of the substrate, we gather all the pieces to construct the Hamiltonian of the semi-infinite system. The surface Green’s function is then computed using the transfer-matrix method and projected onto a wavepacket localized in the surface region. The width and energy of the surface electronic features are obtained from the analysis of such projection. With this approach we get rid of the finite size effects associated with the slab calculations. We have applied this method to the calculation of resonant charge transfer times from adsorbates to metallic substrates. We have focused in the case of core-excited Ar and S on Ru(0 0 0 1) to compare with core-hole clock spectroscopy experiments. We have also used our method to reveal the role of the elastic width in the scanning tunneling spectroscopy measurements of the quasi two-dimensional quantum well state appearing in p(2 × 2) ordered overlayers of Na and Cs on Cu(1 1 1). Here we present a new application of the method to study a more diluted alkali overlayer, the Cu(1 1 1)–(4 × 4)-Na surface. We present results for the relaxed geometries, binding energies, work function change and the position and width of the 3s Na resonance.     

Density functional theory investigation of the photodissociation channels of acetophenone

The photodissociations of acetophenone (C₆H₅COCH₃) have been investigated by density functional theory (DFT) approach. The experimentally observed three photodissociation channels were clarified from the theoretical calculations on the related reactants, transition states (TSs), and products. Two of the three channels, C₆H₅COCH₃ → C₆H₅CO + CH₃ and C₆H₅COCH₃ → C₆H₅ + CH₃CO, were assigned to Norrish I reactions on the potential energy surfaces (PESs) of the lowest triplet state (T₁). And, the first one is more favorable for lower barrier. The subsequent decompositions, C₆H₅CO → C₆H₅ + CO and CH₃CO → CH₃ + CO, were also studied by the similar calculations as above. The third photodissociation channel, C₆H₅COCH₃ → C₆H₅CH₃ + CO, has been documented on the PESs of the ground state (S₀). The third one played a minor role in the photodissociations of C₆H₅COCH₃ for much higher barrier than the first two.     

Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532 nm and 780 nm, dispersive Raman microscopy with excitation laser of 532 nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064 nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96 cm⁻¹ belongs to deformation vibrations of interlayer cations. The band at 200 cm⁻¹ corresponds to deformation vibrations of the AlO₆ octahedron and at 710 cm⁻¹ can be assigned to deformation vibrations of the SiO₄ tetrahedron. The band at 3620 cm⁻¹ corresponds to the stretching vibration of structural OH groups in montmorillonites.     

Nonempirical analysis of the catalytic activity of the molecular environment – optimal static and dynamic catalytic fields for double proton transfer in formamide–formamidine complex

The double proton transfer reaction in model formamide–formamidine dimer mimicking adenine–thymine base pair was investigated. The physical nature of the catalytic activity of the first hydration shell has been analyzed using hybrid variation–perturbation decomposition of intermolecular interaction energy. The differential transition state stabilization energy is dominated by long range electrostatic multipole term, whereas electrostatic penetration, exchange and delocalization terms are negligible or partly cancel each other. This allowed to derive (within electrostatic approximation) the generalized static and dynamic properties of the molecular environment exerting optimal catalytic activity towards canonic → rare and rare → canonic tautomeric rearrangement.     

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s²) to He (1s¹2p¹). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m³, and an energy balance of about −4×10⁵ kJ/mol H₂ compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H₂.     

Studies on the interaction between imidacloprid and human serum albumin: Spectroscopic approach

The interaction between imidacloprid (IMI) and human serum albumin (HSA) was investigated using fluorescence and UV/vis absorption spectroscopy. The experimental results showed that the fluorescence quenching of HSA by IMI was a result of the formation of IMI–HSA complex; static quenching was confirmed to result in the fluorescence quenching. The apparent binding constant K_A between IMI and HSA at three differences were obtained to be 1.51 × 10⁴, 1.58 × 10⁴, and 2.19 × 10⁴ L mol^?1, respectively. The thermodynamic parameters, ΔH° and ΔS° were estimated to be 28.44 kJ mol^?1, 174.76 J mol^?1 K^?1 according to the van’t Hoff equation. Hydrophobic interactions played a major role in stabilizing the complex. The distance r between donor (HSA) and acceptor (IMI) was obtained according to fluorescence resonance energy transfer. The effect of IMI on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy CD and three-dimensional fluorescence spectra, the environment around Trp and Tyr residues were altered.     

A simple fluorescence quenching method for berberine determination using water-soluble CdTe quantum dots as probes

A novel method for the determination of berberine has been developed based on quenching of the fluorescence of thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) by berberine in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of berberine between 2.5 × 10^?8 and 8.0 × 10^?6 mol L^?1 with a detection limit of 6.0 × 10^?9 mol L^?1. The method has been applied to the determination of berberine in real samples, and satisfactory results were obtained. The mechanism of the proposed reaction was also discussed.     

Enhanced frequency upconversion of Sm3+ ions by elliptical Au nanoparticles in dichroic Sm3+: Au-antimony glass nanocomposites

Dichroic Sm³⁺: Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K₂O–B₂O₃–Sb₂O₃ (KBS) by a single-step melt-quench technique involving selective thermochemical reduction. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results indicate that Au⁰ nanoparticles are grown along the (2 0 0) plane direction. The transmission electron microscopic (TEM) image reveals the elliptical Au⁰ nanoparticles having major axis range 12–17 nm. Dichroic behavior is due to elliptical shape of Au⁰ nanoparticles of aspect ratio ～1.2. Au⁰ NPs of concentration of 0.03 wt% (4.1 × 10¹⁸ atoms/cm³) drastically enhances the intensity (～7-folds) of electric dipole ⁴G_5/2 → ⁶H_9/2 red transition (636 nm) of Sm³⁺ ions and then attenuates with further increase in Au⁰ concentration. The magnetic dipole ⁴G_5/2 → ⁶H_5/2 green (566 nm) and ⁴G_5/2 → ⁶H_7/2 orange (602 nm) transitions remain almost unaffected by presence of nano Au⁰. Local field enhancement (LFE) induced by Au⁰ SPR and energy transfer (ET) from fluorescent Au⁰ → Sm³⁺ ions are found to be responsible for the enhancement while reverse ET from Sm³⁺ → Au⁰ and optical re-absorption due to Au⁰ SPR for attenuation.     

Characteristics of Dicesium Plutonium(IV) Nitrate Formation in Separation System of Uranyl Nitrate Hexahydrate Crystal

There is a concerned that Cs and Pu double salt Cs2Pu(NO3)6 is formed under certain conditions in the course of U crystallization. The influence of the Cs concentration in a feed solution on Cs2Pu(NO3)6 formation was thus examined in the U crystallization process. Cesium and Pu were decontaminated after crystal washing with a decreasing Cs concentration in the feed solution. Although Cs remained in the mother liquor at a Cs concentration of 1.0 g/dm³ in the feed solution, Cs2Pu(NO3)6 precipitated at a Cs concentration of 2.2 g/dm³. There is, therefore, a lower limit for the Cs concentration in the feed solution at which Cs2Pu(NO3)6 precipitates, and this limit falls in the range from 1.0 to 2.2 g/dm³ Cs.