I2 Absorption Research Articles

2D and 3D Zn(II) coordination polymers based on 4′-(Thiophen-2-yl)-4,2′:6′,4′'-terpyridine: Structures and features of sorption behavior

Reactions of Zn(II) nitrate, 4′-(Thiophen-2-yl)-4,2′:6′,4′'-terpyridine (ThioTerPy) and terephtalic (bdc) or 2-iodoterephtalic (2-I-bdc) acids result in 2D coordination polymer [Zn2bdc(ThioTerPy)2(OH)2] (1) or 3D metal-organic framework [Zn(2-I-bdc)(ThioTerPy)] (2), respectively. Both compounds were characterized by X-ray diffractometry. For 2, I2 absorption, as well as selectivity of sorption of different organic substrates from mixtures was studied.

A Displacement Measuring Interferometer Based on a Frequency-Locked Laser Diode with High Modulation Frequency

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, the FM interferometer has many advantageous features. The interference signal is a series of time-dependent harmonics of modulation frequency, so the phase shift can be detected accurately using the synchronous detection method. Moreover, the FM interferometer is the most suitable for combination with a frequency-locked laser because both require frequency modulation. In previous research, low modulation frequencies at some tens of kHz have been used to lock the frequency of laser diodes (LDs). The low modulation frequency for the laser source means that the maximum measurement speed of the FM interferometers is limited. This paper proposes a novel contribution regarding the application of a high-frequency modulation for an LD to improve both the frequency stability of the laser source and the measurement speed of the FM interferometer. The frequency of the LD was locked to an I2 hyperfine component at 1 MHz modulation frequency. A high bandwidth lock-in amplifier was utilized to detect the saturated absorption signals of the I2 hyperfine structure and induce the signal to lock the frequency of the LD. The locked LD was then used for an FM displacement measuring interferometer. Moreover, a suitable modulation amplitude that affected the signal-to-noise ratio of both the I2 absorption signal and the harmonic intensity of the interference signal was determined. In order to verify the measurement resolution of the proposed interferometer, the displacement induced by a piezo electric actuator was concurrently measured by the interferometer and a capacitive sensor. The difference of the displacement results was less than 20 nm. To evaluate the measurement speed, the interferometer was used to measure the axial error of a high-speed spindle at 500 rpm. The main conclusion of this study is that a stable displacement interferometer with high accuracy and a high measurement speed can be achieved using an LD frequency locked to an I2 hyperfine transition at a high modulation frequency.

Experimental assessment of the Tenti S6 model for combustion-relevant gases and filtered Rayleigh scattering applications

Accurate descriptions of Rayleigh–Brillouin scattering (RBS) spectra for gas-phase species are important in light scattering measurement techniques including filtered Rayleigh scattering (FRS). The current manuscript targets evaluation of the well-known Tenti S6 model for calculating the RBS spectra for combustion-relevant species over a broad range of temperatures with relevance towards FRS applications in reacting flows. In this work, testing of the Tenti S6 model was performed by comparing measured FRS signals to synthetic FRS signals generated through the combination of the Tenti S6 model and an experimentally verified I2 absorption model. First, temperature-dependent FRS signals were measured for a number of individual gases including Ar, N2, O2, CH4, H2, CO, and CO2 from 300 to 1400 K. Comparisons between the measurements and synthetic FRS signals show excellent agreement (< 4% average difference) over the full temperature range. For pure CO2, rotational Raman scattering effects must be taken into account when comparing measured and synthetic FRS signals. FRS measurements in binary mixtures were performed to assess the commonly used (but not verified) assumption that the total FRS signal from a mixture can be treated as the mole fraction-weighted average of the FRS signals from each component. Measured FRS signals in mixtures with large variations in both molecular weight and Rayleigh scattering cross section show a linear relationship with constituent mole fraction, indicating that this assumption is valid within the kinetic regime. Finally, FRS measurements were performed in near-adiabatic H2/air and CH4/air flames. Comparisons between measured and synthetic FRS signals show excellent agreement over a broad range of equivalence ratios ( $$\phi$$ ), which includes a temperature range of 1100 < T(K) < 2400 and large relative changes in species mole fractions. Overall, the results indicate that the predicted RBS lineshapes calculated using the Tenti S6 model are sufficiently accurate in the context of FRS measurements for the species and temperatures evaluated.

Affinity of ion-exchange membranes for HI–I2–H2O mixture

Electro-electrodialysis (EED) has been applied to thermochemical water-splitting hydrogen production iodine–sulfur process in order to enhance HI in a HI–I2–H2O mixture (HIx solution). In this paper, in order to understand the behavior of the components (I2, H+, I−, and H2O) of the HIx solution in the membranes on absorption equilibrium, each component absorbed in a styrene-grafted poly-(ethylene-co-tetrafluoroethylene) (ETFE-St) membrane and Nafion 212 were evaluated. The behavior of each component in the membrane was as follows. The I2 content in the ETFE-St membrane increased with an increase in the I2 concentration of the immersed HIx solution, whereas I2 absorption by Nafion 212 was minimal. The strong affinity of the ETFE-St membrane for I2 was attributed to the formation of a charge-transfer complex with electron-donating aromatic groups. The ETFE-St membrane absorbed I− (also H+ under the neutral condition) in a HI-molality-dependent manner, whereas I− (H+) absorption by Nafion 212 was negligible. This difference was attributed to the I3−-complex formation in the ETFE-St membrane, which was precluded in Nafion 212. The absorption of H2O was greater for the ETFE-St membrane than for Nafion 212. Incorporation into Nafion 212 would not greatly stabilize H2O while stabilizing H+ by a strong electrical attraction. These results accordingly clarified the affinity of the membranes for the HIx solution based on the excess Gibbs free energy calculated from the measured composition data and the estimated activity coefficients. The excess Gibbs free energy for I2 was larger in the membranes than in the immersed solution, indicating a destabilization of I2 in the membranes. Importantly, this difference agreed with the energy change estimated under the assumption that I2 could form I3− or the charge-transfer complex. The affinity for I2 as well as between the sulfonic acid groups and H+ or H2O is a factor determining the absorbability of the HIx solution.

Ionic Liquid with a Dual‐Redox Couple for Efficient Dye‐Sensitized Solar Cells

A new type of ionic liquid that contains a nitroxide radical (N-O(.)) and iodide as two redox couples, JC-IL, has been successfully synthesized for high-performance dye-sensitized solar cells (DSSCs). Both of the redox couples exhibit distinct redox potentials and attractive electrochemical characteristics. The UV/Vis absorption spectra of JC-IL shows a low-intensity peak compared to the strong absorption of I2 in the wavelength region of 350-500 nm. The high open-circuit voltage of DSSCs with JC-IL is over 850 mV, which is approximately 150 mV higher than that of the DSSCs with a standard iodide electrolyte. The dramatic increase in the standard heterogeneous electron-transfer rate constant leads to an increase in the short-circuit current for JC-IL compared to that of 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO). DSSCs with the JC-IL electrolyte show promising cell efficiencies if coupled with dyes CR147 (8.12%) or D149 (6.76%). The efficiencies of the DSSCs based on the JC-IL electrolyte are higher than those of DSSCs based on either TEMPO electrolyte or standard iodide electrolyte alone.

Highly Efficient Visible-Light-Induced Photocatalytic Activity of Nanostructured AgI/TiO2 Photocatalyst

Nanostructured AgI/TiO(2) photocatalyst was synthesized by a feasible approach with AgNO(3), LiI, and Ti(OBu)(4) and characterized by X-ray diffraction, transmission electron microscopy, angle-dependent X-ray photoelectron spectroscopy, diffusive reflectance UV-vis spectroscopy, Raman spectroscopy, photoluminescence, and the Brunauer-Emmett-Teller technique. The results of characterization reveal that the nanostructured AgI/TiO(2) has a novel core/shell/shell nanostructure of AgI/Ag-I(2)/TiO(2). Compared with TiO(2) (P25) supported AgI, the formation of the nanostructure results in substantial shifting of the absorption edge of AgI to red, enhancement of the absorption intensity, and the appearance of a strong tail absorption above 490 nm, which is assigned to the absorption of I(2) and Ag. Photocatalytic tests show that the nanostructured AgI/TiO(2) photocatalyst exhibited very high visible-light-induced photocatalytic activity for the photodegradation of crystal violet and 4-chlorophenol, which is 4 and 6 times higher than that of P25 titania supported AgI, respectively. The highly efficient visible-light-induced photocatalytic activity of the nanostructured AgI/TiO(2) is attributed to its strong absorption in the visible region and low recombination rate of the electron-hole pair due to the synergetic effect among the components of AgI, Ag, I(20, and TiO(2) in the nanostructured AgI/TiO(2).

Sorption of I2 and CH3 131I on ion-exchange materials from aqueous solutions at 20°C

Sorption of I2 and CH3131I from aqueous solutions at 20°C on the materials obtained by modification of KU-2 cation-exchange resin was studied. It was found that these materials are able to absorb I2 both from distilled water and from a solution whose composition corresponds to the composition of aqueous coolant of the primary circuit of NPPs equipped with reactors of the WWER type, with the distribution coefficients Kd higher than 103 ml g−1 at the ratio V/m = 100 ml g−1. Practically complete absorption of I2 (>95%) is reached in 15 min. It was shown that AV-18 anion-exchange resin extracts CH3131 I from aqueous solution with a distribution coefficient Kd exceeding 300 ml mg−1 at the ratio V/m = 100 ml g−1.

Laser-Induced Fluorescence in Gaseous I2 Excited with a Green Laser Pointer

The use of a green laser pointer to excite fluorescence in gaseous I2 results in an unexpected behavior: on transiting the cell, the beam alternately appears brightly and vanishes completely. This behavior is attributed to temporal changes in the laser’s operating wavelength, likely due to temperature changes of the optical cavity as it warms up under power. As a result, the laser tunes itself into and out of resonance with the I2 absorption lines in the region of the laser gain profile. For this explanation to hold, it is also necessary that the laser operate with relatively high spectral purity, meaning a small number of narrow lasing modes. Spectra recorded for several different pointers display widely varying properties: some pointers operate on a single mode much of the time, while others emit in many weak lines in addition to one or two strong ones. Green laser pointers and an Ar-ion laser are used together to excite gaseous I2, illustrating in a comprehensive way the conditions necessary for lase...

First diode-pumped Yb-doped solid-state laser continuously tunable between 1000 and 1010�nm

We demonstrate that the ytterbium-doped medium Yb:YSO can provide laser oscillation in the 1000–1010 nm wavelength range under diode pumping around 980 nm. Ytterbium-doped Y2SiO5 crystal has been chosen for its high emission cross section around 1 μm combined with a strong absorption line at 978 nm. We have developed an original pumping architecture that permits us to overcome problems due to the small difference between pump and laser wavelengths. In this way, laser emission continuously tunable in the 1000–1010 nm wavelength range has been obtained with more than 100 mW of output power. This kind of laser is the first step toward a metrological source around 500 nm stabilized on an I2 absorption line. Furthermore, 100 mW of laser light has been obtained at 998.5 nm, leading to a remarkably low quantum defect of 2.1%.

Absolute Position of the D′2g(3P2) Ion-Pair State of I2 Determined by Perturbation-Facilitated Optical–Optical Double Resonance

We have reexamined the sequential two-photon absorption of I2 from the X1Σg+ ground state to the lowest D′2g(3P2) ion-pair state using the high vibrational level of the B3Π(0u+) state as an intermediate. The double resonance transition to the D′2g(3P2) state was found to occur through the B3Π(0u+)–b′2u coupled state by hyperfine interaction, which permits to mix the different J levels of different electronic states. We elucidated the B3Π(0u+)–b′2u coupling schemes in the intermediate states. The double resonance spectra recorded for the D′2g(3P2) state in the range v=0–30 were used to determine the absolute energy of the D′2g(3P2) state. The molecular parameters of the D′2g(3P2) state obtained in this study are Y00=40 388.783(2), Y10=103.956 46(57), Y20=−0.207 717(51), Y30=2.199(13)×10−4, Y01=0.020 528 18(62), and Y11=−5.1753(48)×10−5 (all in cm−1 and σ in parentheses). An RKR potential curve constructed using these constants is reported. Combined with the data on the D′2g(3P2)–A′3Π(2u) transition from Zheng et al. (J. Chem. Phys.96, 4877 (1992)), we can locate the A′3Π(2u) v=0 state at 10 096.444(6) cm−1 above the ground state.

Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

We report on quantitative, spatially resolved density, temperature, and velocity measurements on ground-state atomic hydrogen in an expanding thermal Ar–H plasma using two-photon excitation laser-induced fluorescence (LIF). The method’s diagnostic value for application in this plasma is assessed by identifying and evaluating the possibly disturbing factors on the interpretation of the LIF signal in terms of density, temperature, and velocity. In order to obtain quantitative density numbers, the LIF setup is calibrated for H measurements using two different methods. A commonly applied calibration method, in which the LIF signal from a, by titration, known amount of H generated by a flow-tube reactor is used as a reference, is compared to a rather new calibration method, in which the H density in the plasma jet is derived from a measurement of the two-photon LIF signal generated from krypton at a well-known pressure, using a known Kr to H detection sensitivity ratio. The two methods yield nearly the same result, which validates the new H density calibration. Gauging the new “rare gas method” by the “flow-tube reactor method,” we find a krypton to hydrogen two-photon excitation cross section ratio σKr(2)/σH(2) of 0.56, close to the reported value of 0.62. Since the H density calibration via two-photon LIF of krypton is experimentally far more easy than the one using a flow-tube reactor, it is foreseen that the “rare gas method” will become the method of choice in two-photon LIF experiments. The current two-photon LIF detection limit for H in the Ar–H plasma jet is 1015 m−3. The accuracy of the density measurements depends on the accuracy of the calibration, which is currently limited to 33%. The reproducibility depends on the signal-to-noise (S/N) ratio in the LIF measurements and is orders of magnitude better. The accuracy in the temperature determination also depends on the S/N ratio of the LIF signal and on the ratio between the Doppler-width of the transition and the linewidth of the excitation laser. Due to the small H mass, the current linewidth of the UV laser radiation is never the accuracy limiting factor in the H temperature determination, even not at room temperature. Quantitative velocity numbers are obtained by measuring the Doppler shift in the H two-photon excitation spectrum. Both the radial and axial velocity components are obtained by applying a perpendicular and an antiparallel excitation configuration, respectively. The required laser frequency calibration is accomplished by simultaneously recording the I2 absorption spectrum with the fundamental frequency component of the laser system. This method, which is well-established in spectroscopic applications, enables us to achieve a relative accuracy in the transition frequency measurement below 10−6, corresponding to an accuracy in the velocity of approximately 200 m/s. This accuracy is nearly laser linewidth limited.

Beer law constants and vapor pressures of HgI2 over HgI2(s,l)

Optical absorption spectra of the vapor phase over HgI2(s,l) were measured at sample temperatures between 349 and 610 K for wavelengths between 200 and 600 nm. The spectra show the samples sublimed congruently into HGI2 without any observed Hg or I2 absorption spectra. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were derived. From these constants the vapor pressure of HgI2, P, was found to be a function of temperature for the liquid and the solid beta-phases: ln P(atm) = -7700/T(K) + 12.462 (liquid phase) and ln P(atm) = -10150/T(K) + 17.026 (beta-phase). The expressions match the enthalpies of vaporization and sublimation of 15.30 and 20.17 kcal/mole respectively, for the liquid and the beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 kcal/mole, and the intersection of the two expressions gives a melting point of 537 K.

Component Analysis of the Visible Absorption Spectra of I2 and Br2 in Inert Solvents: A Critique of Band Decomposition by Least-Squares Fitting

The absorption spectra of I2 and Br2 dissolved in n-heptane and CCl4 are recorded with high precision in the visible-near-IR spectral range, at temperatures between 15° and 50 °C. The spectra are decomposed into the three contributing transitions (1Πu ← X, B0+u3Π ← X, and A 1u3Π ← X) through simultaneous least-squares fitting of the T-dependent data. The main results of the analysis are as follows. (1) In I2 the weakest A ← X band is virtually identical in shape and intensity in these solvents and in the gas phase, but with small blue shifts in solution. (2) The ∼20% increased absorption of I2 in solution appears to be largely attributable to a doubling in the intensity of the weaker of the two main transitions, 1Πu ← X, which is red-shifted in solution. (3) All three transitions in I2 shift to the red with increasing T, with the strongest effect observed for 1Πu ← X. These differences are not explained by the refraction-index-based relations commonly used to relate gas- and condensed-phase spectra. In the course of this work the method of decomposition analysis by fitting to assumed band shapes has been tested extensively, with the following observations. (1) The much-used 3-parameter Gaussian and log-normal functions do not have enough flexibility to fit single “pure” bands within the experimental precision obtainable from commercial spectrophotometers. (2) The results of such analyses can vary widely with choice of band function. (3) When comparing two such analyses, lower variance is no guarantee of a “truer” resolution. Concerning the labeling of the halogen electronic states involved in the absorption, it is recommended that for consistency the 1Πu state be designated as the C state in all the halogens.

Molecular Constants for the v=0, b1Σg+ Excited State of O2: Improved Values Derived from Measurements of the Oxygen A-Band Using Intracavity Laser Spectroscopy

High-resolution intracavity laser spectroscopy (ILS) absorption measurements have been made on the b–X oxygen electronic transition (the A-band) which has bandheads occurring in the region of 13 165 cm−1. The positions of the lines were determined to an accuracy that is based on calibration with I2 absorption lines using the Laboratoire Aimé Cotton (Orsay) Atlas as reference. Based on the ILS measurements and the more accurately determined positions given by L. R. Brown and C. Plymate (J. Mol. Spectrosc.199, 166–179 (2000)) and with the 3Σg− ground state molecular constants fixed at the values determined by G. Rouillé et al. (J. Mol. Spectrosc.154, 372–382 (1992)), the following values (in cm−1) were found for the molecular constants: T0=13122.2524(1); B0=1.391244(2); D0=5.352(4)×10−6; and H0=−1.2(2)×10−11. These results are compared with values derived from fits of the line positions listed in several other studies of this transition.

Enhancement of the interfacial transfer of iodine by chemical reaction

AbstractEnhancement of the air‐water interfacial transfer of I2 by reaction with I− was investigated in order to evaluate a mechanistic model. Separate systems for evaporation and absorption of I2 were studied. The overall mass transfer coefficient increased from 2 × 10−4 to 2.5 × 10−3 cm/s as I− concentration increased from 10−4 to 10−1 M. At I− concentrations greater than 10−1 M, the interfacial transfer of I2 was gas‐side limited. The model gave a good representation of these results.

Fundamental Reactions in Illuminated Titanium Dioxide Nanocrystallite Layers Studied by Pulsed Laser

Titanium dioxide layers, composed of 5 nm diameter closely packed nanocrystallites prepared by spin coating of concentrated TiO2 sols (titanium isopropoxide hydrolysis), were exposed to pulsed laser photolysis, in the presence as well as in the absence of added reactants. Time profiles in the range 390−700 nm have been studied in the nanosecond time range. TiO2 layers immersed in liquids (acidic or alkaline water, CCl4, CCl4/CBr4 mixture, cyclohexane) show the same absorption vs time profiles as the dry layers. Iodide ions (0.5−7.6 M in water) convert the holes to I2- within less than 10 ns (quantum yield approaching unity is observed at the highest concentration). The absorption of I2- (peaking at 390 nm) is relatively stable during the first 4 μs, in contrast to the decay of the electron absorption which is only slightly different than in iodide-free solutions. This result is unexpected if the decay of the electron absorption is because of electron−hole recombination. Alcohols (methanol and 2-propanol) ...

DETERMINING SPECTROMETER INSTRUMENTAL PROFILES USING FTS REFERENCE SPECTRA

ABSTRACT We describe a new technique for determining the instrumental profile (IP) of an astronomical spectrometer. A known instrinsic spectrum of a reference source is convoluted with a parameterized IP and then compared to a spectrum obtained with the spectrometer to be characterized. Nonlinear least-squares (NLLS) optimization is used to solve for the analytic IP that best reproduces the observed spectrum. This technique is most effective for characterizing the central portion of the IP, out to 1% of the peak. IP recovery is demonstrated using both the Sun and an I2 absorption cell as reference spectra. We also describe a second technique employing singular value decomposition (SVD) to recover an approximate IP by directly inverting a discretized convolution. This second technique is less contstrained and therefore gives poorer results than NLLS, but it is useful when the form of the IP is unknown. Using the NLLS technique, we demonstrate by example that the IP is a function of position in the format of cross-dispersed echelle spectrometers. We also compare our results with laser and thorium emission line profiles. Finally, we present the IP for a range of positions in the format of the Hamilton echelle spectrograph at Lick Observatory and the HIRES echelle at the Keck 10-m telescope.

Iodine Absorption-Line-Stabilized Frequency-Tunable Green Light Using Sum-Frequency Generation of Diode Lasers

A precision frequency-tunable green light source, which involves a frequency reference using a molecular iodine absorption resonance and a tuner, has been demonstrated. The green coherent light was obtained by sum-frequency generation using a 0.82 µm AlGaAs laser and a 1.54 µm distributed-feedback (DFB) laser in a KTP crystal. The reference frequency was locked to an I2 absorption resonance and the residual frequency fluctuation was estimated to be within ±0.5 MHz. A frequency-tunable range of ∼5 THz was obtained. Heterodyne beat signals were obtained to measure the frequency difference between the frequency reference and the tunable output. This system was also proposed for measuring the frequency spacings between different resonances of a molecular absorption spectrum.

Ultrafast photodissociation of I3. Coherent photochemistry in solution

We report a comprehensive study of the UV photolysis of I3− in ethanol solution, using femtosecond time resolved transient transmission experiments. We interpret our results to indicate that with high probability, photoexcitation leads to direct formation of di-iodide ions within 300 fs, which are vibrating coherently. Through our experiments we have been able to determine that the time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. Transmission signals at 620 nm and at 880 nm, which are above and below the λmax of the known absorption of I2−, oscillate at a precisely opposite phase. This and other results presented indicate that through the oscillations we are observing coherent vibration of the I2− photofragment. UV transient transmission experiments have been conducted in order to characterize the time scales for recombination. Preliminary results show that recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I3−. The impulsive nature of the I3− photoexcitation induces coherent symmetric stretching vibration in the ground state tri-iodide population. Finally, the large number of dynamical variables probed directly allows us to record the chronology of this reaction with unprecedented detail. We directly observe a new and potentially informative dynamical variable for this reaction—the absolute phase of fragment vibrations following the photodissociation.

Use of seeded Nd:YAG lasers for high-resolution spectroscopy

The frequency tuning and stabilization of a novel long-pulse seeded Nd:YAG laser is described. The laser frequency was stabilized to +/-8 MHz by locking it to an iodine absorption. A Doppler-free experiment shows the laser linewidth to be in good agreement with the Fourier transform limit of 10 MHz. Molecular hyperfine frequencies and parameters were determined for three I(2) absorption lines. The use of this laser as a pump and a cw probe amplifier for coherent anti-Stokes Raman spectroscopy is illustrated by a scan of the 2v(2)Q-branch transition in CO(2), and the instrumental resolution is found to be 43 +/- 15 MHz.