Concentration Of Iodine Atoms Research Articles

Numerical study of He/CF3I pulsed discharge used to produce iodine atom in chemical oxygen-iodine laser

The pulsed discharge for producing iodine atoms from the alkyl and perfluoroalky iodides (CH3I, CF3I, etc.) is the most efficient method for achieving the pulse operating mode of a chemical oxygen-iodine laser. In this paper, a one-dimensional fluid model is developed to study the characteristics of pulsed discharge in CF3I-He mixture. By solving continuity equation, momentum equation, Poisson equation, Boltzmann equation, and an electric circuit equation, the temporal evolution of discharge current density and various discharge products, especially the atomic iodine, are investigated. The dependence of iodine atom density on discharge parameters is also studied. The results show that iodine atom density increases with the pulsed width and pulsed voltage amplitude. The mixture ratio of CF3I and helium plays a more significant role in iodine atom production. For a constant voltage amplitude, there exists an optimal mixture ratio under which the maximum iodine atom concentration is achieved. The bigger the applied voltage amplitude is, the higher partial pressure of CF3I is needed to obtain the maximum iodine atom concentration.

Dynamics of production of iodine atoms by dissociation of iodides in a pulsed self-sustained discharge

Absorption at the laser transition has been used for the first time to assess the evolution of concentration of iodine atoms in a pulsed self-sustained discharge in mixtures of iodides with a buffer gas such as molecular nitrogen and helium. Dynamics of the iodine atom production is studied by the method of absorption spectroscopy. The dissociation of and () iodides is investigated. The energy required to produce atomic iodine is evaluated. The experimental data obtained for are compared with the results of numerical simulations, their reasonable agreement being demonstrated.

Temperature-Dependent Kinetics of the Vinyl Radical (C2H3) Self-Reaction

The rate coefficient for the self-reaction of vinyl radicals has been measured by two independent methods. The rate constant as a function of temperature at 20 Torr has been determined by a laser-photolysis/laser absorption technique. Vinyl iodide is photolyzed at 266 nm, and both the vinyl radical and the iodine atom photolysis products are monitored by laser absorption. The vinyl radical concentration is derived from the initial iodine atom concentration, which is determined by using the known absorption cross section of the iodine atomic transition to relate the observed absorption to concentration. The measured rate constant for the self-reaction at room temperature is approximately a factor of 2 lower than literature recommendations. The reaction displays a slightly negative temperature dependence, which can be represented by a negative activation energy, (E(a)/R) = -400 K. The laser absorption results are supported by independent experiments at 298 K and 4 Torr using time-resolved synchrotron-photoionization mass-spectrometric detection of the products of divinyl ketone and methyl vinyl ketone photolysis. The photoionization mass spectrometry experiments additionally show that methyl + propargyl are formed in the vinyl radical self-reaction, with an estimated branching fraction of 0.5 at 298 K and 4 Torr.

Novel measurements of atmospheric iodine species by resonance fluorescence

A field instrument has been developed for the purpose of measuring gas-phase atmospheric iodine species in the marine boundary layer. Vacuum UV resonance-fluorescence (RF), generated using a microwave discharge lamp, is employed to detect atomic iodine via the (5p46s)–(5p5) transitions around 178–184 nm. The system can be operated in two modes; either to directly measure ambient iodine atoms, or to measure the total photolabile iodine loading of ambient air, through broadband visible photolysis of photolabile iodine-containing species, with subsequent RF detection of the iodine atoms released. In both cases the instrument allows for the in situ measurement of the species detected, which is advantageous for gathering information concerning their local sources and distribution. The instrument is calibrated through generation of a known concentration of iodine atoms from the photolysis of I2 using a mercury pen-ray lamp. The instrument was deployed for the first time in August 2007 at Mace Head on the west coast of Ireland; initial results from this field trial are presented. Ambient iodine atoms were measured at levels up to 22 ± 4.8 ppt during the day, coinciding with the lowest tides, when Laminaria seaweed beds were exposed. The total photolabile iodine loading was also measured during several night-time and day-time periods and was found to correlate inversely with tidal height. Inferred I2 concentrations based on these measurements indicate levels of several hundred ppt at the Mace Head site. These measurements represent the first direct observations of ambient iodine atoms and measurement of total photolabile iodine in the atmosphere.

Dendrimer-Based Nanosized MRI Contrast Agents

Paramagnetic metals can induce T1 shortening by interaction with free water molecules. Two metal ions, Gadolinium and Manganese, are currently available for human use. Gadolinium-based MRI contrast agents (CAs) can operate using a approximately 100-fold lower concentration of Gadolinium ions in comparison to the necessary concentration of Iodine atoms employed in CT imaging in the tissues. Therefore, numerous macromolecular MRI CAs prepared employing relatively simple chemistry are readily available that can provide sufficient enhancement for multiple applications. Herein, we describe the synthesis, characteristics, and potential applications of dendrimer-based macromolecular MRI CAs in our recently reported libraries. This entire series of dendrimer-based macromolecular MRI CAs have a spherical shape and possess similar surface charges. Changes in molecular size altered the route of excretion. Smaller sized contrast agents, of less than 60 kD molecular weight, were excreted through the kidney resulting in these agents being potentially suitable as functional renal contrast agents. Less hydrophilic and larger sized contrast agents were found better suited for use as blood pool contrast agents. Hydrophobic variants of CAs formed with polypropylenimine diaminobutane dendrimer cores quickly accumulated in the liver and can function as liver contrast agents. Larger hydrophilic agents are also useful for lymphatic imaging. Finally, contrast agents conjugated with either monoclonal antibodies or with avidin are able to function as tumor-specific contrast agents and might also be employed as therapeutic drugs for either gadolinium neutron capture therapy or in conjunction with radioimmunotherapy.

Indirect Measurement of Biologically Important Compounds by Means of X-Ray Microanalysis

The main objective of our work was to investigate the possibility and usefulness of indirect methods in X-ray microanalysis for the quantification of biologically important compounds. Metallothionein-like proteins (MT-like proteins) from kidney and liver, rich in sulfur were chosen as an indicator of heavy metal presence in cells and their environment. Tissues from goldfish (Carassius auratus gibelio) were sampled after short and prolonged periods of exposure to Co+2, CrO4−2, Pb+2, Cu+2 and control treatment and prepared for histochemical staining for peroxidated thiolate groups. Commonly used –S–S– bonds dye (Nitro Red) was replaced with iodine atoms and they were quantified at L line by means of X-ray microanalysis combined with SEM. After fish treatments with heavy metal solutions changes in MT-like proteins and in I atom contents were expected. There was statistically significant decrease in MT-like proteins level in kidney after lead treatment (Pb/C = 0.62). In liver a statistically significant increase in MT-like proteins concentration was observed after chromium, cobalt and lead ions treatment in comparison to control animals. The following ratios were noted: 3.04 for Cr/C, 2.18 for Co/C and 2.10 for Pb/C. Our finding indicates that the method of indirect measurement of MT-like proteins in fish and other animal tissues is possible. The concentration of iodine atoms is above their detection level by EDS and their changes are possible to identify. During histochemical procedures it is worth taking into account sample preparation methods which might disturb the quality and quantity of the analysed material.

Atomic iodine production in a gas flow by decomposing methyl iodide in a dc glow discharge

The production of atomic iodine for an oxygen — iodine laser is studied by decomposing methyl iodide in a dc glow discharge in a vortex gas flow. The concentration of iodine atoms in discharge products was measured from the atomic iodine absorption of the radiation of a single-frequency tunable diode laser at a wavelength of 1.315 μm. Atomic iodine concentrations sufficient for the operation of an oxygen — iodine laser were obtained. The concentration of atomic iodine amounted to 3.6 × 1015 cm-3 for a pressure of the carrying argon gas of 15 Torr. The discharge stabilisation by a vortex gas flow allowed the glow discharge to be sustained in a strongly electronegative halogen-containing gas mixture for pressures up to 20 Torr.

Two-Channel Thermal Unimolecular Decomposition of Alkyl Iodides

The competition between the C−I bond fission and the four-center HI elimination in the thermal unimolecular decomposition of C3−C4 alkyl iodides has been investigated at temperatures of 950−1400 K and pressures around 1 atm by a shock tube technique. The concentration of iodine atoms was followed by atomic resonance absorption spectrometry. For primary iodides, the absolute rate constants were measured at temperatures of 950−1100 K. The branching fractions for C−I bond fission channels were determined for all isomers of C3 and C4 alkyl iodides at temperatures of 950−1400 K. A drastic change in the branching fraction for the C−I bond fission channel was observed from primary iodides (0.6−0.9) to secondary iodides (0.2−0.4), and further to tertiary iodide (<0.05), which was mainly ascribed to the lowering of the threshold energy for the HI elimination channel from primary to secondary (by ∼14 kJ mol-1) and from secondary to tertiary (by ∼20 kJ mol-1) iodides. The α-CH3 substituent effect to the activation e...

HeI photoelectron spectroscopy (UPS) of iodine atoms

High concentrations of iodine atoms are directly obtained from methyl iodide on a Double-Chambers UPS Machine II, which was built specifically to detect transient species. A complete and well-resolved HeI photoelectron spectrum of iodine atom is recorded for the first time using a modified sample inlet system. Five peaks which come from the transition from ground state 2P 3 2 iodine atom to 3P 2,1,0, 1D 2 and 1S 0 ionic states have clearly been observed. The relative photoelectron intensities of ionic states are fairly close to their statistical ratios.

Diode laser detection of iodine atom hyperfine transitions during and after infrared multiphoton excitation and dissociation of CF 3I with short pulse CO 2 lasers

The iodine atom concentration has been measured by time-resolve absorption spectroscopy for all hyperfine levels on the I( 2P 3 2 )→I( 2P 1 2 )) transition during and after the multiphoton excitation of CF 3I, using a tunable diode laser in the near infrared at 1.3 μm. The experiments have been performed under collision free conditions with a time resolution of about 1 ns. Using CO 2 laser pulses of different temporal shape, the nonlinear intensity dependence of the multiphoton excitation process and the previously measured steady state rate constants have been confirmed. Detection at different hyperfine transistion frequencies and charging the relative orientation of the polarization of the pump and probe laser showed statistical behaviour for the population of the hyperfine levels and for the orientation of the iodine atoms. Using CO 2 laser pulses of specially tailored temporal shape the theoretically predicted intensity fall-off for the steady state rate constant has been found experimentally.

Temperature dependence of the collisional deactivation of I ( 2P [formula omitted]) by I 2 and O 2 from 300 to 600 K

The collisional deactivation of excited iodine atoms I(5p 5 2P 1 2 ) by I 2 and O 2 has been studied as a function of temperature from 295 to 600 K. The decay of the excited iodine atom concentration following dye laser photolysis of molecular I 2 was detected by time-resolved fluorescence at 1.315 μm. The temperature dependence of quenching rate constants by molecular I 2 and O 2 was found to be weak over this range.

Isoméirsation cis–trans de l'azobenzène catalysée par l'iode. III

The cis–trans isomerization of azobenzene can be catalyzed by iodine. The rate constant for the reaction of cis-azobenzene with iodine atoms was determined as 2 ± 1 × 106 mol−1 1 s−1, i.e. a much larger value than that pertaining to other isomerizable systems. This very high reactivity of cis-azobenzene allowed the demonstration of surface effects which were unexpected in the liquid phase. A method for estimating low concentrations of iodine atoms can be based on this catalyzed isomerization. [Journal translation]

Conformation of polymer analogs in solution. X‐ray scattering from ethylene oxide oligomers carrying iodine atoms at the chain ends

AbstractThe angular dependence of X‐ray scattering intensities of solutions of diiodobenzenes was compared with that of iodobenzene solutions containing the same concentration of iodine atoms. The data yielded interiodine distances of 3.6, 5.9, and 6.9 Å for the ortho, meta, and para isomers, respectively, in good agreement with the known values of 3.52, 5.92, and 6.84 Å. The same method was applied to a study of inter‐iodine separations in ICH2CH2(OCH2CH2)nI (n = 1, 2, 3) using CH3CH2OCH2CH2I as the monoiodo analog. Experimental limitations preclude detailed interpretation of the data in terms of a probability distribution of the end‐to‐end distances of these model compounds. The intramolecular inter‐iodine distances were characterized by the first minimum and the first maximum of the scattering function i(s) = ΔĪcorr/f, where ΔĪ is the difference in the scattering intensity from solutions of the diiodo and monoiodo compounds corrected for polarization, fI is the form factor of iodine and s = 4π sin Θ/λ, 2Θ is the scattering angle and λ the wavelength of the X‐rays. The molecular chains of all three oligomers were significantly more expanded in m‐xylene than in ethanol, the difference increasing with increasing chain length. A conformational analysis was carried out for ICH2CH2OCH2CH2I choosing the energies for conformational transition so as to yield a conformational distribution with the observed average square dipole moment and scattering function in non‐polar media. The contraction of the molecule in ethanol is much larger than can be accounted for by the reduction in the COULOMBic energy of dipole interaction in a medium of higher dielectric constant.

The Recombination of Iodine Atoms Generated by a C. W. Argon Ion Laser

Abstract The rate constants of iodine-atom recombination in various foreign gases were determined by measuring the relative concentrations of iodine atoms in the photostationary state, through irradiation by a c.w. argon-ion laser at 4880 Å. The relative concentration has been obtained from the absorption intensity for the emission line from an iodine discharge lamp at 1830 Å. The rate constants have been given for the diffusion of iodine atoms and for the second-order recombination of iodine atoms. The values of the diffusion rate constants in various foreign gases have been compared with the calculated values. The logarithmic second-order rate constants in various gases were plotted against their ionization potentials. The plot yielded a straight line, indicating that the formation of the charge-transfer complex between iodine atoms and foreign gas molecules is important in the recombination process, as has been suggested by Porter et al.

Photodissociation of Molecular Iodine

AbstractElectron spin resonance has been used to monitor iodine atom concentrations as functions of iodine pressure, light intensity, and magnetic field strength during in situ irradiation in the banded region and the continuum of I2 B(3Πou+). Evidence for direct predissociation as a major deexcitation process for I2(B) exists in the parallelism of [I.] vs. [I2] curves in the two regions of photoexcitation. The steady‐state iodine atom concentration varies with the square root of incident light intensity; its dependence on molecular iodine concentration is complex.

Mechanism of the ``Bimolecular'' Hydrogen—Iodine Reaction

The rate of photochemical production of hydrogen iodide in a hydrogen—iodine system irradiated with 5780-Å light was measured and found to be proportional to the square of the iodine atom concentration. Absolute light intensities were determined and rate constants were calculated for the termolecular reaction H2+2I→2HI at 417.9°, 480.7°, 520.1°K. The previously obtained thermal data in the range 633°—738°K were treated considering one of the elementary reactions to be the termolecular reaction and not H2+I2→2HI; the rate constants obtained have the same Arrhenius parameters as those from the photochemical measurements. The bimolecular reaction, H2+I2→2HI, does not occur. Two mechanisms consistent with the photochemical and the thermal data are H2+2I→2HI; H2+I+M=H2I+M, H2I+I→2HI. The specific rate calculated for the termolecular reaction is k=(6.66±0.5)×107 exp (−5310±85/RT) liter2 mole−2·sec−1.

Elementary reactions in the photochemical oxidation of methyl iodide

The photochemical oxidation of gaseous methyl iodide at room temperature was investigated under conditions such that oxygen molecules were competing with iodine molecules and/or iodine atoms for reaction with methyl radicals. The molecular iodine produced in the oxidation was measured by means of its light absorption. A balanced photomultiplier system for the determination of small percentage light absorptions is described. Analysis of the results shows that the contribution of the methyl radical + iodine atom recombination is negligible compared with the methyl radical + iodine molecule reaction for the relative concentrations of iodine atoms and iodine molecules involved. The variation with pressure of the ratio of the rate constant of the methyl radical + iodine molecule reaction to that of the methyl radical + oxygen molecule reaction indicates that the main reaction of methyl radicals with oxygen is a third-order one. This is assumed to be their association to form methylperoxy radicals. Methyl iodide is approximately ten times as efficient as carbon dioxide in acting as a third body for this association. The relative rate of a simultaneous second-order reaction of methyl radicals with oxygen has also been determined. From comparison with other work, the probable orders of magnitude of the rate constants of these elementary reactions of the methyl radical are deduced.

Studies in energy transfer I. The combination of iodine atoms

An experimental study has been made of the velocity of combination of iodine atoms in the presence of a number of added gases in order to investigate the factors influencing energy transfer. The reaction cell, containing iodine at a pressure of 0.097 mm Hg and a known pressure of third body, is irradiated with a flash from a discharge tube. The concentration of iodine atoms as recombination proceeds is determined by measuring the light absorption of the system with a photomultiplier tube. The reaction is second order with respect to the concentration of iodine atoms, and first order with respect to the third body. The third-order rate constants vary from 0.97 x 10-32mol.-2cm6s-1when helium is added to 224 x 10-32mol-2cm6s-1for mesitylene. The velocity of combination at 127° C has been found to be approximately 0.4 time the velocity at 20° C for six different additives. This factor seems to be independent of the nature of the additive. The efficiencies of the different additives is primarily determined by the magnitudes of their intermolecular force fields, which are reflected in their boiling-points and critical temperatures.