Recombination Of Iodine Atoms Research Articles

Product channels of the reactions of O2(b1[formula omitted

Laser-induced fluorescence (LIF) experiments have been employed to evaluate the branching fractions for the product channels for O2(b1Σg+) reactions with M = CO2, N2, H2, C2H4, N2O, H2O CH4 and I2 molecules. O2(b1Σg+) was formed by exciting ground-state oxygen molecules with pulses from a tunable dye laser, and the kinetics were followed by observing the temporal profiles of the O2 b1Σg+ − X3Σg-, O2a1Δg − X3Σg-, and I2 A′3Π2u, A3Π1u − X1Σg+ fluorescence signals. It has been found that O2(b1Σg+) is quenched to O2(a1Δg) with a branching fraction 1.00 ± 0.05 for all tested molecules except iodine. The reaction of O2(b1Σg+) with I2 has been found to have two dominant product channels, O2(X3Σg-) + I2(A′3Π2u or A3Π1u) and O2(X3Σg-) + 2 I(2P3/2) with branching fractions of 33 ± 7% and 67 ± 7%, respectively. Emission from I2(A′3Π2u or A3Π1u) molecules formed in recombination of iodine atoms in the gas phase was detected in the near IR.

Solvation Ultrafast Dynamics of Reactions. 12. Probing along the Reaction Coordinate and Dynamics in Supercritical Argon

In this paper, our focus is on the influence of the solvent density on the caging, recombination dynamics, and the nature of the reaction coordinate of iodine in supercritical argon at pressures of 0−2500 bar. Femtosecond probing with widely tunable pulses allows us to directly resolve the geminate recombination of iodine atoms and the subsequent relaxation processes. A nonzero recombination yield is found at argon pressures as low as 200 bar, and this yield increases strongly with increasing solvent density. The mechanism involves recombination onto the A/A‘ states. At high pressures, a large fraction of the iodine atoms undergo an ultrafast “in-cage” recombination which is measured on the subpicosecond time scale at 2500 bar of argon. In addition, a fraction of the iodine atoms break through the solvent cage and begin a diffusive motion through the rare-gas solvent. Experimental evidence is presented and indicates that this diffusive motion leads to reencounters and subsequent recombination of the geminate iodine pair. This diffusive recombination occurs on a significantly longer time scale than the rapid “in-cage” recombination. The newly-formed iodine molecules undergo vibrational relaxation within the A/A‘ state, and the dynamics of this process and its dependence on the solvent density are revealed. A key concept here is the solvent density-induced control of the rigidity of the first solvent shell surrounding the dissociating iodine atoms. As shown before [Liu et al. Nature 1993, 364, 427], such studies of solvation present a unique opportunity of examining the microscopic influence of the solvent structure on reaction dynamics in clusters and solutions.

A more accurate method of measuring the cross section for the 52P1/2→52P3/2transition of atomic iodine in photodissociation lasers based on dynamic self-diffraction

We have developed a new method for measuring the cross section for the 52P1/2→52P3/2 transition of atomic iodine in photodissociation lasers. The inverse recombination of iodine atoms is monitored via dynamic self-diffraction of the laser radiation in the active medium. We have measured the cross section in mixtures of H-C3F7I and CF3I with Xe. This new method substantially increases the accuracy with which the cross section can be measured. Our results are highly reproducible, with a dispersion of no more than 3%.

The very fast chemiluminescent reaction I(5p 52P [formula omitted]) + I(5p 52P [formula omitted]) → (M) I 2(B O u+, υ′) → I 2(X O g+, υ″) + hν

The method of quantitative laser induced chemiluminescent kinetic spectroscopy (QLICKS) is developed for the study of chemiluminescence reactions. This method enables us to determine spectral distributions of chemiluminescence rate constants k cl(λ) (photon cm 3/particle 2 s nm) and total chemiluminescence rate constants k cl (photon cm 2/particle 2 s). QLICKS is applied to the study of the iodine atom recombination accompanied by radiation according to I(5p 5 2P 1 2 ) + I(5p 5 2P 3 2 ) → (M) I 2(B O u +, υ′) → I 2(X O g +, υ″) + hν (i). Iodine atoms are obtained by photolysis of RI = CF 3I, CF 3CFICF 3 at λ = 266 nm. Assuming quantum yields of the I( 2P 3 2 ) and I( 2P 1 2 ) atoms formation equal to 0.1 and 0.9, respectively, the following values of the total chemiluminescence rate constant are determined: k i = (10 +10 −5, 7.4 +7 −4 and 3.0 +3 −1.6) × 10 −15 photon cm 3/particle 2 s for M = He, Ar and CF 3CFICF 3 respectively. The rate constant of the process 2I(5p 5 2P 1 2 ) → (M) I 2(1 u) → I 2(1 g) + hν (ii) is estimated to be k ii = (3.5 +3.5 −1.7) × 10 −17 photon cm 3/particle 2 s for M = CF 3I, CF 3CFICF 3. Kinetic and spectral features of reaction (i) can be described only in terms of the I*…M or I…M complex formation. Process (i) may be considered as representative of a wide class of recombination reactions accompanied by radiation proceeding through complex formation with a particle M and having very high rate constants. The existence of such very fast chemiluminescent reactions provides real opportunities for the development of recombination lasers operating on molecular transitions.

Kinetics of reactions of methylperoxy and 2-hydroxyethylperoxy radicals produced by the photolysis of iodomethane and 2-iodoethanol

The molecular modulation technique coupled with UV absorption spectroscopy has been used to investigate the UV spectra and kinetics of reactions of the methylperoxy radical (CH{sub 3}O{sub 2}) and the 2-hydroxyethylperoxy radical (HOCH{sub 2}CH{sub 2}O{sub 2}), generated by the 254-nm photolysis of the organic iodides CH{sub 3}I and HOCH{sub 2}CH{sub 2}I: RI + h{nu}({lambda}=254 nm) {yields} R + I and R + O{sub 2} + M {yields} RO{sub 2} + M. These are believed to be CH{sub 3}OOI and HOCH{sub 2}CH{sub 2}OOI formed as intermediates in the RO{sub 2}-chaperoned recombination of iodine atoms. Both CH{sub 3}O{sub 2} and HOCH{sub 2}CH{sub 2}O{sub 2} were found to obey second-order kinetic behavior owing to removal by a series of reactions initiated by the self-reactions: CH{sub 3}O{sub 2} + CH{sub 3}O{sub 2} {yields} products and HOCH{sub 2}CH{sub 2}O{sub 2} + HOCH{sub 2}CH{sub 2}O{sub 2} {yields} products. Additional measurements made over the temperature range 268-350 K indicated that this parameter displays a weak negative temperature dependence. E/R was found to have a value of {minus}220 {plus minus} 72 K at 760 Torr, and a value of {minus}92 {plus minus} 53 K at 10.8 Torr. The parameter k{sub 10obs}/{sigma} had a value of (6.8 {plus minus}more » 0.4) {times} 10{sup 5} cm s{sup {minus}1} at 230 nm (p = 760 Torr, T = 298 K). Assuming the photolysis of HOCH{sub 2}CH{sub 2}I leads exclusively to the production of HOCH{sub 2}CH{sub 2}O{sub 2}, the following values of {sigma}(230 nm) and k{sub 10obs} were concluded: {sigma}(230nm)= (2.35 {plus minus} 0.25) {times} 10{sup {minus}18} cm{sup 2} molecule{sup {minus}1} and k{sub 10obs} = (1.60 {plus minus} 0.17) {times} 10{sup {minus}12} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}.« less

Radiation induced gas-dynamic refractive index changes in an iodine laser oscillator

Due to the exothermic recombination of ground state iodine atoms I with free radicals C/sub 3/F/sub 7/ to the parent molecule C/sub 3/F/sub 7/I, the gaseous medium of an iodine laser oscillator is subject to spatially inhomogeneous heating. This causes temperature and pressure gradients leading to gas-dynamic motion and thus to density and refractive index changes perturbing the optical quality of the laser medium. Since the strength of the recombination reaction depends directly on the laser intensity via the process of stimulated emission, this coupling can lead to self-termination of the laser radiation. This phenomenon is experimentally and theoretically investigated. >

Reactions of electronically excited iodine: quenching of the A' state

Geminate recombination of condensed-phase iodine atoms produces a diffuse red absorption which has been assigned to population in the lowest excited A'(/sup 3/..pi../sub 2u/) state. Based upon this assignment, condensed-phase quenching of the A' state by ground-state I/sub 2/ has been studied by picosecond absorption spectroscopy. Quenching occurs by a bimolecular reaction I/sub 2/(A') + I/sub 2/ ..-->.. I/sub 4/* ..-->../sup ./ I/sub 3/ + I. The bimolecular rate constant is 9.5 x 10/sup 9/ M/sup -1/ s/sup -1/, which is approximately the diffusion-limited rate. The product I/sub 4/* or I/sub 3/ has a weak (epsilon less than or equal to 200 M/sup -1/ cm/sup -1/) absorption in the 550-800-nm region.

Studies of chemical reactivity in the condensed phase. II. Vibrational relaxation of iodine in liquid xenon following geminate recombination

The geminate recombination of iodine atoms in xenon solutions, has been studied by monitoring the transient absorptions at wavelengths between 350 and 1000 nm.(AIP) ;m

Geminate recombination of iodine atoms in solution: A generalized langevin treatment including the effect of electronically inelastic transitions

The geminate recombination of iodine atoms in liquid carbon tetrachloride has been modeled theoretically using the generalized Langevin model of Adelman, which accounts for the cage effect, and allowing for electronically inelastic transitions between various I 2 potential curves by the semiclassical model used earlier by us. The results show that electronic inelasticity is an important feature (providing a factor of 2 or greater change in the recombination probability) of the recombination process. They are also in excellent agreement with available experimental results.

New I2 emission from iodine atom recombination reaction

In the UV photolysis of perfluorinated alkyl iodides, iodine atoms in the two spin states 2P12 and 2P32 of the electronic ground state are formed. The atoms recombine in a three-body collision to form iodine molecules. The reactive collision of I(2P32) with I(2P12) leads to I2(B) which is detected by its chemiluminescence spectrum. The observed spectra contain an additional emission which is discussed to be the result of a transition from a higher excited I2 state correlating with two I(2P12).

Effect of electronic transition dynamics on iodine atom recombination in liquids

The Langevin stochastic trajectory model used by Hynes, Kapral, and Torrie [J. Chem. Phys. 72, 177 (1980)] to describe secondary recombination of iodine atoms in solution has been generalized to allow for electronically inelastic transitions between the ten I–I potential curves that dissociate to ground state iodine atoms. The electronic transitions are treated via the Miller–George version of the Tully–Preston surface hopping model. The main qualitative result is that electronically inelastic processes substantially slow down the rate (and ultimate probability) of recombination. It is also seen that the electronic inelasticity changes from being strong at large r, where an essentially Boltzmann distribution over the various electronic states is maintained, to being weak at small r, where the distribution is far from Boltzmann.

Diffusion theory and picosecond atom recombination

We attempt to describe our picosecond iodine recombination data using simple diffusion theory. The physical picture is simple. Recombination of iodine atoms is the result of the diffusive motion of two iodine atoms, with such parameters as viscosity and temperature together with the diffusion theory governing the motion. The difference between most tests of diffusion theory and the present one is the extremely short time scale of our experimental data. We are thus close to, if not already in, the regime where the solvent structure is noncontinuous. In this regime the fundamental hypothesis of diffusion theory is invalid and one would not expect diffusion theory to be valid. We compare several different formulations of the diffusion equation solutions using different boundary conditions. The comparisons of each of these treatments with the experimental data fails. A discussion of the implications of this result, as well as some suggestions for improving the applicability of diffusion theory is presented.

Reactions of excited I*(2P1/2) and unexcited I(2P3/2) iodine atoms in perfluoroalkyl radicals

A method of investigating reactions of excited and unexcited atoms is discussed. It is based on pulsed photolysis of molecules with simultaneous passage of laser radiation through the working medium. The method proposed is used to investigate the reactions that accompany the photolysis of the molecules RI(CF3I, n-C3F7I, i-C3F7I). The rate constants of the recombination of iodine atoms into I2 in the presence of RI molecules are calculated for the atoms I(2P3/2) and I*(2P1/2), as are the recombination constants of the radicals R into R2 and with the atoms I*(2P1/2) and I(2P3/2) into the RI molecule. It is shown that the I(2P3/2) atoms are much more active in the recombination into Ia and RI than the I*(2P1/2) atoms. The role of the investigated reactions in the kinetics of a photodissociation iodine laser (PDIL) is discussed. The results are compared with the published data.

On the determination of the stored optical energy of an atomic iodine laser amplifier from the energy measured in the free running mode

An exact determination of the stored optical energy of an amplifier from the energy measured in the free running mode has been difficult for the iodine laser because of the influence of the recombination of ground state iodine atoms with radicals to the parent molecule on the population of the lower laser level. A formula is derived relating the stored optical energy to the one measured in the free running mode with due consideration of this effect.

Heteronuclear recombination of chlorine and iodine atoms

Various works dealing with the flash photolysis studies of IClI are discussed. Some results wherein relatively inert bodies such as N/sub 2/ and CO/sub 2/ are reported to catalyze the formation of IClI much faster than the homonuclear recombination that produces I/sub 2/ or CL/sub 2/ are questioned and reexamined. Results of recent studies indicate that 99% of the Cl atoms will have reacted within a period of 4 ..mu..s. Since all reaction times reported in the flash photolysis studies were measured from 50 ..mu..s after the onset of the flash, essentially all the Cl atoms are thought to have disappeared before any measurements could have been made. The authors then conclude that reported values for the rate constant for heteronuclear recombination of Cl atoms did not actually have any basis of fact, but the values reported for the IClI catalyzed recombination of I atoms are considered to be valid.

ChemInform Abstract: THE RECOMBINATION OF IODINE ATOMS IN THE PRESENCE OF NITRIC OXIDE

AbstractDie Rekombination von I‐Atomen nach der Blitzphotolyse von I, in einer Ar‐Atmosphäre in Gegenwart von NO wird durch die Reaktionsfolge A, B, Cerklärt.

The temperature dependence of the cage effect in the gas phase

The photodissociation of iodine has been studied in the gas phase by laser flash photolysis. The decrease of the quantum yield with increasing ethane and propane pressure has been interpreted in terms of the cage effect. As the temperature is increased a less pronounced cage effect is observed. The trends in the measured quantum yields with changing temperature and pressure agree with model calculations for dissociation in a viscous continuum. However the simple model applied is not useful for quantitative predictions. A small decrease of the second order rate constant for iodine atom recombination has been observed with increasing temperature.

The recombination of iodine atoms in the presence of nitric oxide

AbstractThe recombination of iodine atoms following the flash photolysis of iodine in the presence of nitric oxide is interpreted through the mechanism equation image with k1 = 3.5 × 109 l.2/mol2·sec; k2 ≈ 1 × 1011 l./mol·sec; k3 = 2.1 × 107 l./mol·sec at 298°K; E3 = 11 kJ/ mol; and ΔH°1 = 76 ± 6 kJ/mol. Lower and upper limits for the equilibrium constant are also established. The absorption spectrum of INO has been extended down to 223 nm and extinction coefficients for the region of 223–310 nm and 360–460 nm have been measured.

Application of the shock tube unsteady expansion wave technique to the study of chemical reactions

An unsteady expansion wave was generated through rupture of a secondary diaphragm by an incident shock wave in a shock tube to study the three-body recombination of iodine atoms. The application to chemical reaction studies has been made possible through an extension of the usable flow time, and a theoretical treatment enables the effect of coupling of chemical reaction to gas flow to be taken into account. Species concentrations along different particle paths in the expansion wave are given to show the three types of flow regime (frozen, nonequilibrium and equilibrium) which can be accessed by this technique. Using these results, theoretical and experimental I2 concentration profiles are compared as a function of time in the nonequilibrium regime.

ChemInform Abstract: RECOMBINATION OF IODINE ATOMS BY FLASH PHOTOLYSIS OVER A WIDE TEMPERATURE RANGE. VIII. MOLECULAR IODINE IN MOLECULAR OXYGEN

Chemischer InformationsdienstVolume 8, Issue 28 Physical Inorganic Chemistry ChemInform Abstract: RECOMBINATION OF IODINE ATOMS BY FLASH PHOTOLYSIS OVER A WIDE TEMPERATURE RANGE. VIII. MOLECULAR IODINE IN MOLECULAR OXYGEN R. E. ANTRIM, R. E. ANTRIMSearch for more papers by this authorG. BURNS, G. BURNSSearch for more papers by this authorJ. K. K. IP, J. K. K. IPSearch for more papers by this author R. E. ANTRIM, R. E. ANTRIMSearch for more papers by this authorG. BURNS, G. BURNSSearch for more papers by this authorJ. K. K. IP, J. K. K. IPSearch for more papers by this author First published: July 12, 1977 https://doi.org/10.1002/chin.197728030AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue28July 12, 1977 RelatedInformation