Iodine Fluorescence Research Articles

Vibrational and rotational dependence of electric field induced predissociation of I2

An electric field induced predissociation of the B 2 Π0 u + state of molecular iodine to the unbound 1g state is studied by the observation of laser induced fluorescence of iodine. The variation of the induced predissociation rate with the vibrational level of the B state indicates that the unbound state crosses the B state near ν = 0 on the inner limb. The transition dipole moment between the two states is 0.13±0.07 debye.

Vibrational and rotational dependence of electric field induced predissociation of I2

An electric field induced predissociation of the B 2 Π0 u + state of molecular iodine to the unbound 1g state is studied by the observation of laser induced fluorescence of iodine. The variation of the induced predissociation rate with the vibrational level of the B state indicates that the unbound state crosses the B state near ν = 0 on the inner limb. The transition dipole moment between the two states is 0.13±0.07 debye.

Simultaneous multiple-point velocity measurements using laser-induced iodine fluorescence

A technique is demonstrated for measuring velocity at multiple locations in a plane of a gaseous flowfield using Doppler-shifted absorption with fluorescence detection from iodine molecules, excited by a sheet of tunable single-axial-mode argon-ion laser radiation at 514.5 nm. Measurements were made simultaneously at 10,000 points in an iodine-seeded supersonic flowfield with a 100 x 100 element photodiode array camera and were found to agree well with a numerical solution for the velocity field. The accuracy with which a component of velocity can be measured is limited, in the current approach, by the iodine linewidth to about +/-5 m/sec.

Laser-induced fluorescence visualization on supersonic mixing nozzles that employ gas-trips

A laser-induced iodine fluorescence visualization technique has been refined and used extensively to study supersonic cold-flow mixing. In particular, visualization studies were performed in the mixing region between supersonic slit nozzles that employed gas trips for enhanced mixing. The nozzles were operated with roomtemperature helium under simulated chemical laser flow conditions. The primary objective was to develop insight into the trip-enhanced mixing phenomenon. Three-dimensional information was therefore acquired on the size, shape, location, structure, and interaction of the primary, secondary, and trip jets under both trip-on and trip-off operation. This has led to postulations on the existence of three trip-induced convective mechanisms that appear to contribute to enhanced mixing. The active mechanisms, as well as the dominant mechanism, appear to depend upon: the type of trip configuration used, the nozzle width, and the flow field location since one mechanism appears to dominate in the primary nozzles and another in the secondary nozzles.

The use of 1-anilino naphthalene-8-sulfonate (ANS) for studying the effects of iodination on thyroglobulin conformation

19 S thyroglobulin purified from porcine thyroids was fractionated according to its iodine content by means of isopycnic centrifugation at the equilibrium in RbCl. Some fractions of the gradient were titrated with 1-anilino naphthalene-8-sulfonate, a molecule which does not fluoresce in water but becomes highly fluorescent in organic solvents or when it interacts with proteins. An inverse and linear relationship was found between iodine content and fluorescence observed (at 475 nm) in the plateau region of the titration curves. The analysis of these curves permitted the evaluation of the dye-protein-binding parameters. It appears that by decreasing the iodine content from ∼-77 to ∼-38 iodine atoms per molecule, the number of sites for the 1-anilino naphthalene-8-sulfonate linearly increases from ∼-4 to ∼-14. The association constants, on the contrary, do not vary appreciably, ranging from 4 to 6 × 10 7 M −1. The monotone depolarization of 1-anilino naphthalene-8-sulfonate fluorescence, observed with thyroglobulin molecules of increasing iodine content, suggests that conformational transitions take place concomitantly with the iodine organification. Neither deglycosylation nor changes in pH (6.2–9.0), modify the stoichiometry of the interaction. The findings of the present work are consistent with the hypothesis that thyroglobulin is arranged in similar or even identical structural domains and that iodination gradually modulates the protein conformation.

Application of x-ray fluorescence to the study of iodine distribution and content in the thyroid.

We have been developing an X-ray fluorescence system designed to determine iodine distribution and content in the thyroid. The X-ray fluorescence unit is composed of a 80 KV X-ray excitation beam and a Si(Li) semi-conductor detector. The angle between the X-ray beam and the axis of the detector is 24 degree. Two single channel analyzers (SCA) are used, the first one corresponding to the K alpha peak and the other to the background. The SCA signals are digitised so that the two corresponding images may be processed using a computer. After subtracting the background, an image is obtained that represents the iodine distribution alone, and the iodine content of the whole thyroid or a part of it can be determined with a reproducibility of +/- 5%. A good correlation (r=0.98) between iodine chemical analysis and iodine fluorescence analysis was obtained for 13 patients.

Locking of cw dye laser emission onto the wavelength of molecular fluorescence by intracavity gain: Example I2

A cw dye laser can be locked onto wavelengths corresponding to iodine (I2) fluorescence when the fluorescing samples are placed inside the dye laser cavity. The sensitivity of the dye laser to intracavity gains is analogous to its well-known sensitivity to intracavity losses. Gains as low as 0.0001 were detected. In particular, the 5145 Å emission of an Ar+ laser was used to excite I2 molecules inside of a tunable dye laser cavity to the v′=43, J′=12 and/or 16 level (s) of the B 3Π0u+ ground electronic state. The dye laser was then progressively tuned to stimulate emission to the v′′=10–15,J′′=11, 13 and or 15, 17 levels of the X1 Σ0g+ ground electronic state. The efficiency of the dye laser assisted I2 laser was 1–2 orders of magnitude higher than for the Ar+ pumped cw I2 laser. The locking of the dye laser to the I2 fluorescence frequencies was found to be a function of the specific vibrational and rotational quantum numbers. When the dye laser is operated above threshold, spatial hole burning severely limits the fraction of the laser power locked onto I2 fluorescence wavelengths.

Electric field-induced predissociation of I 2(B 3Π 0+ u)

An electric field can couple the B 3Π 0+ u state of molecular iodine so predicted, unbound 0 + g and 1 + g states, inducing predissociation of the B state. This effect is studied by observation of the electric field modulated, laser induced fluorescence of iodine. The dependence of the induced predissociation rate on the vibrational level of the B state indicates that an unbound state (probably the 0 + g) crosses the B state near υ = 3−4 on the outer limb. The transition dipole moment between B and the unbound state is 0.03–0.04 D.

Photofragment fluorescence following ultraviolet laser multiple-photon excitation of CH 3X molecules (X = OH, Br, I)

Photofragment fluorescence following excitation of the molecules CH 3I, CD 3I, CH 3Br and CH 3OH, with an inert-gas halogen exciplex laser, is reported. Strong fluorescence from the A 2Δ and B 2Σ − states of CH and CD, and atomic iodine fluorescence, is observed. The mechanism for the excitation process is discussed and it is suggested that simultaneous two-photon absorption is the dominant mechanism in these systems.

UV photolysis of n-C 3F 7I. Radiative lifetime of metastable iodine atoms

The photolysis of n-C 3F 7I and C 2F 5I has been studied with a frequency doubled dye laser at fixed frequency in the UV by detection of time resolved resonance fluorescence of the metastable iodine formed. The rate coefficient for quenching of I( 2P 1 2 ) by n-C 3F 7I has been obtained as k = (4.6 ± 0.3) × 10 −17 cm 3 molecule −1s −1. This value is by more than an order of magnitude lower than published values. Further proof is given for the value of the radiative lifetime of the metastable atoms which was obtained recently by this experimental method. This answers questions raised by Husain et al. on this subject in this journal.

Investigation of the fluorescence of molecular iodine in the 340 nm band

Results are presented of observations of the fluorescence of iodine vapor, subjected to cw optical pumping, as a function of the temperature and pressure of the SF6, N2, Ar, Xe, He, and Kr buffer gases. It is shown that an increase of the fluorescence in the 340 nm band with rising buffer gas pressure is accompanied by a decrease in the iodine fluorescence in the 250–330 nm band. The efficiency of the action of the buffer gas depends on its molecular weight and on the wavelength of the exciting light. The intensity depends on the buffer gas used. An estimate is made of the rate of quenching of the fluorescence by iodine molecules in the ground state kqτ =(3.0±0.30)×10−18 cm3. For Xe, kqτ = (1.2±0.6)×10−18 cm3. It is shown that the fluorescence quantum efficiency η does not depend on the mixture temperature up to 425 °C. The value of η for optical pumping (λ = 190 nm) of a mixture of iodine vapor and 5 atm SF6 is η = 0.04±0.02 and for a mixture with 1.5 atm Ar, is η = 0.05±0.02.

Fluorescence yield of individual hyperfine components in B state of I2: a test of hyperfine predissociation

A monomode dye laser is used to excite the iodine fluorescence on a molecular beam. The relative fluorescence quantum yield of some hyperfine sublevels are measured for 49 rovibrational levels of the B3 Pi 0+u state. These quantum yields are found to be in agreement with the theory of the hyperfine predissociation and some values of the predissociation parameters are deduced.

Fluorescence and quenching of the 3400 Å bands of iodine

The fluorescence of iodine was excited with white light from a capillary flash lamp, and emission of the 3400 Å bands was monitored in Ne, Ar and CF 4. It is concluded that I 2 D 1Σ + u, formed initially, is collisionally transferred to I 2 3Π 2 g . Rate coefficients for removal of the two electronic states by O 2, CO 2 and C 3H 8 are derived, to their spontaneous decay rates. It is suggested that the formation of IO in the flash photolysis of I 2, O 2 mixtures probably arises from the reaction of I 2 D 1Σ + u with O 2. The possibility of an optically pumped ultraviolet iodine laser is discussed.

Persistence of MJ following vibrational and rotational energy transfer in molecular iodine excited by a single mode tunable dye laser

Excitation of iodine fluorescence with a single mode tunable dye laser allows extensive observation of features from vibrationally and rotationally transferred states populated through collisions. We have measured the circular polarisation of these features and observe a very high degree of polarisation following both vibrational and rotational energy transfer: thus transitions from states following Δ J′ = 60 and Δν′ = 1, Δ J′ = 60 are still highly polarized. This implies strong conservation of M J throughout energetic inelastic collisions.

Proceedings: An inherently stable system for measuring tissue iodine using its K-absorption edge.

An experimental system for detection of small concentrations of iodine in tissue is described.A collimated beam of lanthanum Ka1 and Ka2 x rays is passed through phantoms of iodine and water. The energies of these 2 x rays straddle the K-absorption edge of iodine and are differentially absorbed by the iodine phantom. After emerging from the phantom, the 2 x rays are separated by a stable iodine filter placed in the beam path with resulting photoelectric absorption of the Ka1 x rays on the high side of the K-edge of iodine. This results in production of isotropically propagated iodine fluorescence x rays which are counted by a surrounding NaI(Tl) crystal-photomultiplier detector. The Ka2 x rays are counted by a second, more distant detector. The ratio of the Ka2/Ka1 x rays is determined by simultaneously counting the scintillations produced in these 2 detectors. In the phantom, an iodine concentration of 1 mg/cm2 produces a change in this ratio of about 3 per cent. The change in this ratio is about 1,000 t...

Observation of a New Effect on the Fluorescence of Molecular Iodine Excited by Ionized Argon or Krypton Lasers

Iodine vapor excited by certain lines of ionized argon or krypton lasers emits an intense fluorescence. We have observed large variations in light intensity which can neither be interpreted as a Hanle effect due to the applied fields, nor to predissociation.

Magnetic Quenching of Iodine Fluorescence Excited by a 6328 Å He/Ne Laser

The extent of the magnetic field induced quenching of the fluorescence from the (v′ = 6, J′ = 32) and (v′ = 11, J′ = 128) levels of the B 3Π (Ou+) state of I2 has been measured. A He/Ne laser operating at 6328 Å has been used to excite the fluorescence. Combining these measurements with earlier results obtained for the higher vibrational levels allows us to determine the shape of an Ou− repulsive potential energy curve which crosses the B-state curve. Since the v′ = 6 level is observed to be quenched much more strongly than the levels of higher v′, this Ou− curve crosses the B-state curve at a low v′ value.

Resonance fluorescence and absorption spectra of molecular iodine: identification and molecular assignment

Molecular levels in the B3Π0+u state excited by several Ar+ and Kr+ laser lines and the Cd I emission line at 5086 Å have been positively identified following an extended rotational analysis of bands of the B–X system of I2.

Iodine Fluorescence Excited by the He–Ne 6328-Å Laser

Iodine Fluorescence Excited by the He–Ne 6328-Å Laser

Predissociations Induced by a Magnetic Field

A theoretical study of field-induced predissociations is presented. It is found that the rate of predissociation in general depends on the rotational quantum number. However, for several limiting cases the rotational dependence cancels out. The vibrational effect on predissociation is treated in the semiclassical approximation. Comparison is made with the recent experimental results on the magnetic quenching of iodine fluorescence by Degenkolb, Steinfeld, Wasserman, and Klemperer.