Vibrational relaxation induced population inversions in laser pumped polyatomic molecules

Conditions for population inversion in laser pumped polyatomic molecules are described. For systems which exhibit metastable vibrational population distributions [slow vibration—translation/rotation (V—T/R) relaxation], large, long lived inversions are possible even when the vibrational modes are strongly coupled by rapid collisional vibration—vibration (V—V) energy transfer. Overtone states of a hot mode are found to invert with respect to fundamental levels of a cold mode even at V—V steady state. Inversion persists for a V—T/R relaxation time. A gain of 4 m^?1 for the 2v₃ → v₂ transition in CH₃F (λ ≈ 15.9 μ) was found assuming a spontaneous emission lifetime of 10 s for this transition. General equations are derived which can be used to determine the magnitude of population inversion in any laser pumped, vibrationally metastable, polyatomic molecule. A discussion of factors controlling the population maxima of different vibrational states in optically pumped, V—V equilibrated metastable polyatomics is also given.     

Determination of rates of collision-induced vibrational and intramultiplet transitions for YO(A2II) molecules in Ar- and N2-diluted flames

Rate contants for single-step collisional transitions between specified vibrational and electronic-doublet levels of YO(A²II) molecules were determined under multiple-collision conditions at constant total gas pressure. We recorded simultaneously the thermal emission spectrum and the fluorescence spectra induced by a cw dye laser tuned successively at various vibronic transitions. We used premixed N₂-diluted or Ar-diluted H₂-O₂ flames at 1 atm and = 2350 K, containing YO vapour. Relative rate constants (normalized to the quenching plus radiative de-excitation rate constants) were obtained by solving a set of simultaneous master equations involving the stationary laser-induced population increments. Absolute rate constants were derived therefrom by determining indirectly the fluorescence efficiency. Exoergic doublet-mixing collisions appeared to have greater probabilities than Δv = ?1 or ?2 transitions and were about equally probable as quenching collisions. Ar and N₂ were about equally efficient as collision partner. The rate constants of each process and of its reverse were compared with detailed-balance. The rotational levels in the pumped band appeared to preserve the e/f symmetry index partially.     

The effect of hyperfine structure on the collisional relaxation of the thallium atom excited by laser beam

We present a theoretical analysis of the transient population inversions which appear in the optically pumped thallium (6² P _1/2, 6² P _3/2, 7² S _1/2) atom. We account for the hyperfine structure and we assume that the pumping occurs in the presence of buffer gas. Numerically computed time dependencies of population differences between the Zeeman sublevels of hyperfine levels of the 7² S _1/2 and 6² P _{1/2, 3/2} states are given. It is demonstrated how the described effects depend on the strength of the atom-field coupling and buffer gas pressure. The role of resonant and nonresonant pumping is explained.     

Hyperfine interactions at 57Fe in octaethylhaemin

Mössbauer measurements on octaethylhaemin have been made between 4.2 and 300 K, and (at the lower temperature) in applied magnetic fields of up to 50 kG. From a spin hamiltonian treatment the saturation value of the hyperfine field at the ⁵⁷Fe nucleus is found to be 495 kG, and the splitting parameter for the ferric ion levels by the axial ligand field is D = 8.0 cm^?1. The electric field gradient 1/2e²qQ = +0.93 mm s^?1.     

Collision cross sections for excitation energy transfer in Na* (3P 1/2)+K(4S 1/2)⇔Na*(3P 3/2)+K(4S 1/2) processes

The cross sections for the excitation energy transfer between the 3² P _J states of sodium atoms by collisions with ground-state potassium atoms have been measured by resonant Doppler-free two-photon spectroscopy, where the population densities of directly pumped and collisionally excited Na(3P _J )(J=1/2, 3/2) levels were probed by counter-propagating Na(3P _J ) → Na(4D _{3/2, 5/2}) excitation and detected with the thermionic diode. Cross sections of σ(3P _1/2 → 3P _3/2)=190 Ų±20% and σ(3P _3/2 → 3P _1/2)=100 Ų±20% were found. The theoretical calculations taking into account the long-range interaction termsR ^?6,R ^?8 andR ^?10 yield a value σ(3P _1/2 → 3P _3/2)=165 Ų. On the basis of these long-range interaction potentials the differential cross section has been calculated and compared with recently published experimental data. Very good agreement between the theoretical and experimental data was found.     

Quasi-stationary detection of transient absorption of a dissociating molecule

Using the forth harmonic of a Nd-YAG laser at 266 nm TlI was dissociated and the dissociation was observed by a transient absorption due to a transition from the repulsive potential, which correlates to T1 (6p ² P _3/2) and I, to the repulsive potential with the asymptote T1 (7s) and I. The experiment is performed with quasi-stationary spectroscopy in the nanosecond time domain, but detects transients effects by asymmetric absorption profiles in the frequency domain. Simulations applying Bloch equations with time dependent molecular energies are able to reproduce the observations and give information on the difference potential between the two molecular states involved and the transition dipole moment. The results are also in good agreement with fs experiments from other authors.     

Quenching dynamics study on photoinduced excited triplet duroquinone by TEMPO in 1,2-propandiol

Chemically induced dynamic electron polarization (CIDEP) spectrum and transient absorptive spectrum are recorded in photolysis of duroquinone (DQ) in 1,2-propanodiol (PG). Durosemiquinone neutral radical DQH^• and PG ketyl radical \textCH₃[(\textC)\dot]\textOHCH₂\textOH{\text{CH}}_{3}{{{\dot{\text{C}}}\text{OHCH}}}_{2}{\text{OH}} are produced through hydrogen transfer reaction from PG to ³DQ*. When stable radical TEMPO is added to DQ/PG solution, photolysis results in CIDEP on TEMPO, which can be interpreted as a quartet precursor radical-triplet pair mechanism (QP-RTPM). There is competition between PG and TEMPO to quench ³DQ*. The CIDEP intensity of DQH^• decreases with the increase of TEMPO concentration. The quenching dynamics in photolysis of DQ/TEMPO/PG system is analyzed in detail. Based on the dynamics analysis and the measurement of the lifetime of ³DQ* by its transient absorbance decay, the quenching rate constant of ³DQ* by TEMPO in PG is obtained as 1.34 × 10⁷ L mol⁻¹ s⁻¹. This quenching rate constant is closely diffusion-controlled.     

Complexation study and spectrofluorometric determination of the binding constant for diquat and p-sulfonatocalix[4]arene

The interactions between diquat (DQ) and p-sulfonatocalix[4]arene (C4S) were studied in an aqueous solution as a function of the ionic strength. Evidence for the formation of a complex between DQ and C4S was obtained using fluorescence measurements, while the stoichiometry of the complex was confirmed as 1:1 for DQ/C4S using UV–vis spectroscopy. The ionic strength had no influence on the stoichiometry of the complex, but exerted a significant influence on the complexation constant, K_c, decreasing with an increase in the ionic strength. The thermodynamic complexation constant, K_c′, was computed as 5.25±1.11×10⁷ using the extended Debye–Hückel law. The rate constants for the heterogeneous electron transfer for the reduction of DQ at an electrode surface were evaluated as 0.150±0.010 cm s^?1 in the absence of C4S and 0.065±0.010 cm s^?1 when C4S was added to the solution in a 1:1 ratio.     

Mixed-valence trinuclear cluster (2dn,dn+1); Influence of the electronic coupling on the magnetic properties

The influence of electronic processes on the magnetic behavior of the mixed-valence trinuclear clusters (2dⁿ, dⁿ⁺¹) is discussed. The problem is solved by means of a pseudoparticle formalism by assuming competing effects such as electronic transfer, and localization of the extra-particle due to different transfer pathways or different sites…. The magnetic susceptibility is derived for significant values of the characteristic parameters in the cases n = 1, 3, 5. Finally, the magnetic behavior of Fe₃O(CH₃COO)₆L₃, with L = H₂O or pyridine, is discussed on the basis of the proposed model.     

The electric saturation of molecular alignment in liquid nitrobenzene as studied by NMR

Quadrupolar line splittings in the ¹⁴N and ²H spectra of liquid nitrobenzene, induced by an external electric field, were studied up to very high electric field strengths (E ≈ 1.8 × 10⁷ V m^?1). At moderate fields the line splittings are proportional to E²; at the fields attained in the present experiments higher order effects become detectable. This phenomenon is related to electric saturation: the change of the permittivity in a strong electric field. Nitrobenzene has been reported to exhibit an anomalous saturation effect of the permittivity, but the saturation of the molecular alignment appears to be normal     

Duroquinonerhodium(I) complexes. Crystal structure of [Rh(DQ)(C6H5Me)]PF6

The preparation of cationic arenerhodiiim(I) complexes of the type [Rh(DQ)-(arene)]PF₆ (DQ = duroquinone; arene = C₆H_6-nMe_n, n duroquinone complexes with Group VB donor ligands are described. The crystal structure of [Rh(DQ)(C₆H₅Me)]PF₆ has been determined by X-ray diffraction. The compound crystallizes in the P2₁/n space group, in a unit cell of dimensions a 15.9866(5), b 11.8438(3), c 9.9968(3) Å, β 98.473(4)Å. The structure was solved by Patterson and Fourier methods and refined to R and R_w values of 0.062 and 0.076, respectively. The Rh atom is coordinated to a toluene group (η⁶) and a duroquinone ligand (η⁴), which eclipse each other. Both ligands are distorted to adopt boat-like conformations.     

Vibration excitation of no in its collisional quenching of O2 (1▵g)

Infrared emission of NO from levels up to v = 4 is observed in its gas phase quenching of O₂(¹ ?_g). The predominance of population of the highest accessible level of NO (v = 4) is due to matching of energies.     

Valence band and Zn 3d energy levels in Me2Zn from photoelectron spectra and pseudopotential ab initio calculations: electric field gradients in gas phase Zn compounds

The He I and X-ray photoelectron spectra of the valence levels and Zn 3d levels in Me₂Zn have been recorded. The orbital ionization potentials are compared with those obtained from our ab initio pseudopotential calculation on Me₂Zn. There is excellent agreement between predicted and observed values for the outer valence orbitals. The Zn 3d level in Me₂Zn in split into five peaks due to the combined effect of spin-orbit splitting and crystal field splitting. The major part of the splitting is due to the asymmetric C⁰₂ crystal field term which transforms like the electric field gradient. The derived C⁰₂ terms for Me₂Zn and ZnCl₂ are ?0.0169 ± 0.0007 eV and ?0.011 eV respectively. The observed and calculated splitting confirms an electrostatic (rather than a bonding) origin. The C⁰₂ value for Me₂Zn is consistent with that observed recently for Me₂Cd.     

4-Hydroxy-3,5-pyridinedicarboxylic Acids: Synthesis,Complexation Properties Towards Fe(III), Al(III), Cu(II), Zn(II), Human Serum Albumin,and Cellular Toxicity

4-hydroxy-3,5-pyridinedicarboxylic acid (DQ58) and 4-hydroxy-1-methyl-3,5-pyridinedicarboxylic acid (DQ71508) have been synthesized, and their Fe(III), Al(III), Cu(II), and Zn(II) coordination properties have been studied by potentiometry, UV–Vis spectroscopy (in the case of Fe(III), Al(III), Cu(II)), ¹H-NMR (for Al(III)) and EPR (for Cu(II)). The thermodynamic results were used to model the extent of the toxic metal ions decorporation (Fe(III) or Al(III)) in the presence of the essential metal ions (Cu(II) or Zn(II)). DQ58 and DQ71508 were demonstrated to interact with human serum albumin (HSA), which is assumed to be the main serum transporter of the chelators, and binding constants have been obtained by ultrafiltration. IC₅₀ values of 5.185 × 10^?3 and 1.033 × 10^?3 mol·L^?1 were collected after 24 and 48 h of treatment with DQ71508 towards human embryonic kidney HEK-293 cells, demonstrating the relatively low cytotoxicity of this compound. According to these results, both DQ58 and DQ71508 seem to be potential candidates for Fe chelation therapy, and DQ58 is a better Fe(III) chelator than DQ71508.     

Mechanism of thermal energy charge transfer reactions: + N2. Analysis of isotopic data

The

+ N₂ charge transfer reaction has been studied in an ICR spectrometer using both ¹⁴N₂ and ¹⁵N₂. The N⁺/N₂⁺ branching ratio was measured from the zero collision limit (ca. 1 × 10^?5 torr total pressure) to collisional saturation (ca. 1 × 10^?3 torr total pressure) for He/N₂ ratios of 5, 10, 50 and 100. The data were analyzed by solving exactly the kinetic equations and the associated power absorption equations. A positive pressure dependence in the N⁺/N₂⁺ branching ratio was observed indicating some N⁺ is formed from collisional dissociation of excited

ions. Comparison is made with recently published data from other groups and previously published data from this laboratory.     

A CIDEP study of photolysis of duroquinone/hydrogen-donor homogeneous and triton micelle solutions

The CIDEP spectra of transient radicals during photolysis of the duroquinone (DQ)/ethylene glycol (EG) system in acid, basic, and micellar environments were measured with a home-made highly time-resolved ESR spectrometer. In the DQ/EG homogeneous solution, the enhanced emissive CIDEP signal of the neutral durosemiquinone radical DQH^• was observed. When the DQ/EG solution at pH 9 or the DQ/EG/TX-100/H₂O micelle system was photolyzed, the CIDEP signal of the duroquinone anion radical (DQ^•−) was obtained. When the DQ/EG solution at pH 2.5 was irradiated, the CIDEP signal of DQH^• appeared. These experimental results indicate that the neutral radical DQH^• was formed by proton transfer from EG to ³DQ*, and that DQ^•− was formed by dissociation of DQH^• accompanying polarization transfer.     

Synthesis and antibacterial activity of methylated N-(4-N,N-dimethylaminocinnamyl) chitosan chloride

The methylated chitosan containing different aromatic moieties were synthesized by two steps, the reductive amination and the methylation. The chemical structures of all methylated derivatives, methylated N-(4-N,N-dimethylaminocinnamyl) chitosan chloride (MDMCMCh), methylated N-(4-pyridylmethyl) chitosan chloride (MPyMeCh), and N,N,N-trimethyl chitosan chloride (TMChC) were characterized by ATR-FTIR and ¹H NMR spectroscopy. The molecular weights of the methylated chitosan derivatives were determined by gel permeation chromatography. The results revealed that the molecular weights of chitosan and N-aryl chitosan derivatives could be reduced by the methylation process. The degree of N-substitution (DS) and the degree of quaternization (DQ) were calculated by ¹H NMR ranged from 50% to 76%, and 28% to 82%, respectively. The water solubility of the methylated chitosan derivatives decreased with increasing concentration and pH. The antibacterial studies of these methylated chitosan derivatives were carried out by using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) methods against Escherichia coli ATCC 25922 (Gram-negative) and Staphylococcus aureus ATCC 6538 (Gram-positive) bacteria. It was found that the MDMCMCh showed higher antibacterial activity than TMChC while MPyMeCh exhibited reduced antibacterial activity against both bacteria at the same DQ level. In comparison to each of the chemical structure, it was found that the antibacterial activity was not only dependent on the DQ but it was also dependent on the positively charged location and the molecular weight.     

Effect of increasing pH value on the structural,optical and magnetic properties of yttrium iron garnet films prepared by a sol–gel method

Yttrium iron garnets (Y₃Fe₅O₁₂, YIG) nanoparticles thin films with different pH values (pH 1, 2, 3, 4 and 5) were prepared by a sol–gel method. The films were deposited on quartz substrates using a spin coating technique. Annealing of the films was performed at 900 °C in air for 2 h. The structural analysis using an X-ray diffractometer (XRD) exhibited that all films were single phases regardless the differences in pH value. The lattice parameters calculated from the XRD patterns revealed that the distortion of lattice occurred at a high pH value. The crystallites sizes of films also increased from 27.6 to 33.3 nm when the pH value increases from 1 to 5. The films were high agglomeration due to increasing of pH value which caused difficulty to measure the grain size. The films with different pH values showed transmission >80 % in visible range. Additionally, the absorption coefficient (α) of films was found to be of the order of 10⁷ cm^?1. A strong absorption of the films caused by charge transfer transition centered in UV and optical transitions between crystal field levels within the 3d levels of Fe³⁺ ions. The YIG films exhibit highest saturation magnetization value of 76 emu/cm³ at pH 1. The increment of pH value up to 5 caused a decreasing of coercive field due to multidomain formation and the easy movement of the domain walls.     

Effects of electric fields and electric field-gradients on X-ray scattering factors and the compton profile of hydrogenic atoms

Analytic expressions for the modification of the hydrogenic atom X-ray atomic scattering factor and Compton profile due to a proton at distance R are derived. It is shown that electric field-gradient effects (order R^?3) are comparable in importance to electric field effects (order R^?2).     

Dependence on effective saturation of numbers of singlet peaks in one- and two-dimensional separations

The average numbers of singlet peaks in one-dimensional (1D) and two-dimensional (2D) separations of randomly distributed peaks are predicted by statistical-overlap theory and compared against the effective saturation. The effective saturation is a recently introduced metric of peak crowding that is more practitioner-friendly than the usual metric, the saturation. The effective saturation absorbs the average minimum resolution of statistical-overlap theory, facilitating the comparison of 1D and 2D separations by traditional metrics of resolution and peak capacity. In this paper, singlet peaks are identified with maxima produced by a single mixture constituent. Their effective saturations are calculated from published equations for the average minimum resolution of 1D singlet peaks, and from equations derived here for the average minimum resolution of 2D singlet peaks. The fractions of peaks that are singlets in 1D and 2D separations are predicted by statistical-overlap theory as functions of saturation but are compared as functions of effective saturation. The two fractions differ by no more than 0.033 at any effective saturation between 0 and 6, when the distribution of peak heights is exponential and the edge effect is neglected. This result shows that 1D and 2D separations of randomly distributed peaks are about the same in their ability to separate singlet peaks as maxima, when assessed relative to effective saturation. Empirical equations in effective saturation are reported for the fractions of peaks that are singlets. It is argued that the effective saturation is a good metric for comparing separations having different average minimum resolutions.