Possibility of separating the isotopes127I and129I with the aid of a photodissociation iodine laser

A method for separating iodine isotopes is proposed, based on the large difference between the rate constants of the excited I*(²P_1/2) and unaxclted iodine atoms with radicals CF₃ and with Cl₂ molecules, and on the possibility of selectively acting on the₁₂₇I atoms in the states²P_1/2 and²P_3/2 by radiation from a photodissociation R¹²⁷I iodine laser (λ = 1.315 μm). The possibility of separating the pure isotope¹²⁹I and the mixture¹²⁷I with¹²⁹I is investigated.     

Collisional enhancement of the I(52P12) emission at 1.3μm by parent molecules CF3I,C2F5I,i-C3F7I and n-C3F7I

The magnetic dipole transition I(5²P_{$\text{1}\text{2}$}-5²P_{$\text{3}\text{2}$}) at 1.3152 μm is shown to be enhanced by collisions of the metastable iodine atoms with the parent RI molecules CF₃I, C₂F₅I, i-C₃F₇I and n-C₃F₇I. The enhancing mechanism is exciplex emission of the RI·I(5²P_{$\text{1}\text{2}$}) molecule at 1.3 μm, with different rates for each iodide. The influence of this effect on the measurement of the quantum yields to I(5²P_{$\text{1}\text{2}$}) and of the respective reaction rates by infrared fluorescence is discussed.     

Photolysis of compounds with P−I and As−I bonds

Detailed experimental investigations are reported of the parameters of lasing on the transition²P_1/2→²P_3/2, λ = 1.3 μm of atomic iodine upon photodissociation of the molecules (CF₃)₂AsI and (CF₃)₂PI. The light source was an IFP-5000 flash lamp. The experimental data are used to determine the sequence of the basic reactions that accompany the photolysis of the molecules (CF₃)₂AsI and (CF₃)₂PI and to determine the energy parameters of the generated radiation.     

Multiphoton ionization of iodine atoms and CF<Subscript> 3</Subscript>I molecules by XeCl laser radiation

We report about effective ionization of iodine atoms and CF₃I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF₃I molecules is the I⁺ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(²P_3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I^*(²P_1/2). The ionization of the CF₃I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms.     

Reactive scattering of a supersonic deuterium atom beam : D+Br2, CF3I,C2F5I,C3F7I

Reactive scattering of D atoms with Br₂, CF₃I, C₂F₅I and C₃F₇I molecules has been studied at an initial translational energy E = 5·3 kJ mol^-1 using a supersonic beam of D atoms seeded in He. Deuterium halide product is scattered in the backward direction with respect to the incident D atoms, with substantial energy disposed into product translation in all cases. The fraction of the total available energy which is disposed into product translation, is greater for the fluoralkyl iodides than for Br₂ and decreases slightly along the series CF₃I, C₂F₅I, C₃F₇I. These results demonstrate that the reaction of D atoms with fluoroalkyl iodides occurs only in collisions at small impact parameters with strong repulsion between the reaction products. The potential energy surfaces for the reactions of the fluoroalkyl iodides are similar to that for the D + Br₂ reaction but involve the release of a still greater proportion of the reaction exoergicity in the exit valley of the surface. Only a small fraction, if any, of the product repulsion is transferred to internal excitation of the product fluoroalkyl radical.     

Characterization of a Br(2P1/2)–CO2(1001-1000) transfer laser driven by photolysis of iodine monobromide

2 laser operating on the 10⁰1-10⁰0 transition at λ=4.3 μm and pumped by E –V energy transfer from Br(²P_1/2) has been demonstrated. The dynamics and performance of this device were characterized by observing the time-resolved stimulated emission and the steady-state spontaneous side fluorescence after photolysis of IBr or Br₂ by a frequency-doubled Nd:YAG laser or Ar⁺ laser, respectively. Although the E –V excitation kinetics are favorable, rapid vibrational relaxation limits laser action to CO₂ pressures of less than 1 Torr. Numerical modeling of laser pulse shapes and the dependence on IBr and CO₂ pressure and photolysis energy establish a relatively high gain of 0.33%/cm, a CO₂-pressure-dependent optical loss of 0.04–0.06%/cm, and an efficiency of 2×10^-5 4.3-μm-laser photons per incident photolysis photon. The CO₂ fluorescence after photolysis of a fixed Br₂/CO₂ gas mixture decreases as a function of photolysis time by about 30%/h, indicating the photolytic production of an important quencher. Received: 23 June 1997/Revised version: 23 September 1997     

Development of the Chemical Oxygen-Iodine Laser (COIL) with chemical generation of atomic iodine

This article addresses the development of a Chemical Oxygen-Iodine Laser (COIL) with alternative chemical ways of generating atomic iodine. Injection of atomic iodine as opposed to molecular iodine has the potential to improve the COIL efficiency. This paper describes two chemical methods for generating iodine atoms based on the gas phase reactions of hydrogen/deuterium iodide with fluorine or chlorine atoms, which are also produced chemically. Simplified one-dimensional gas dynamic modeling that describes the stream-wise profiles of species concentrations within both reaction systems is used to gain a theoretical understanding of both reaction systems under COIL conditions. The modeling results are used for the design of an experimental device and the interpretation of experimental data. The first experimental investigation studies the production of iodine atoms produced from reactions of Cl with HI. Atomic iodine yields of 70–100% in nitrogen are obtained, and the gain on the I(² P _1/2)–I(² P _3/2) transition in a flow of singlet oxygen is measured. Received: 7 October 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +420-2/8689-0527, E-mail: kodym@fzu.cz     

Collisional depolarization and redistribution of laser radiation in near resonance with a2 P 3/2↔2 S 1/2 transition

We have investigated experimentally and theoretically the spectral distribution and collisional depolarization of laser light near resonant to the Na transition 3² S _1/2?3² P _3/2 scattered from a Na/Ar mixture in a cell (n _Na≈4.0×10¹⁰cm^?3,n _Ar≈1.0×10¹⁷cm^?3). In particular, at excitation intensity of ≈3mW/mm² and bandwidth of <10 MHz, intensityI _F and linear polarization degreeP _F of theD ₂-fluorescence component of the scattered spectrum have been measured as functions of the laser detuningΔλ _L from theD ₂-resonance within two regions: 1) ¦Δλ _L ¦-Doppler-width; 2) 20≧¦Δλ _L ¦/Δλ _D ≧1. Within the first region the influence of hyperfine splitting as well as pumping of the hyperfine and Zeeman sublevels of 3² S _1/2 was studied in detail. Using an overall, total collision cross section for depolarization of 3² P _3/2 state atoms, calculations on the basis of the theory of redistribution reproduce qualitatively, but in a consistent manner, the experimental functionsI _F(Δλ_L) andP _F (Δλ _L ). The possibility to derive differential cross sections fromP _F (Δλ_L) is discussed.     

A photolyticallyQ-switched photolytic iodine laser

A novel, repetitively pulsed, photolyticQ-switching scheme has been demonstrated on a 1.315 m (² P _1/2² P _3/2) cw photolytic iodine laser using an intracavity cell containing either IBr or ICl. When the cell is irradiated with a KrF laser (=248 nm), I(² P _3/2) atoms are produced and lasing ceases due to the introduction of loss into the laser cavity. Lasing resumes, however, following recombination of the atoms into the parent molecule. Experimental evidence is presented which indicates that the laser's shut-off time is a function of excimer laser energy and the pressure of buffer gas in the cell.     

Photodissociation of the molecules SiCl3I and SiF3I

The parameters of lasing based on the transition of atomic iodine and occurring upon photodissociation of the molecules SiCl₃I and SiF₃I are experimentally investigated. The light source employed was a coaxial xenon-filled flash lamp of original construction. The main chemical reactions that accompany the photolysis of the molecules SiCl₃l and SiF₃I and determine the energy characteristics of the f~enerated radiation are analyzed.     

Penning ionization electron spectroscopy of CO,HCl, HBr and of triatomic molecules N2O,NO2, CO2, COS and CS2

The energy of electrons released in ionization of di- and triatomic molecules by He (2¹S, 2³S), Ne and Ar (³P_{0, 2}) metastable atoms was measured. Attention was concentrated on the determination of peak shifts and peak form in order to elucidate new features of the mechanism of ionization with respect to ionization of atoms. In ionization by He (2¹S) atoms, asymmetric peak forms and greater shifts towards lower electron energy were found than in ionization by He (2³S) atoms. A tentative explanation for peak shifts in terms of orientation of molecules during the collision and of molecular orbitals involved in ionization was proposed. Effects due to J values of metastable atoms and molecular ions were described. The ionization of electronegative molecules (NO₂) probably takes place already at large particle separation because of mixing with the X⁺ABC^? ionic state which, on recombination, ionizes into X + ABC⁺ + e.     

Laser isotope separation of carbon by multiple IR photon and subsequent UV excitation of CF3I molecules

A new approach to laser isotope separation is considered. It is based on collisionless multiple photon ir laser excitation and subsequent uv laser dissociation of vibrationally excited molecules. TEA CO₂ and excimer XeF, XeCl lasers are used for ir excitation and uv dissociation, respectively. The products of photolysis (C₂F₆) are enriched with¹²C.     

紫外激光离解四氯化钛产生的钛原子的受激喇曼散射

紫外激光(259—300nm)离解四氯化钛产生了大量钛原子,它们主要处于钛原子的基态a³F₂和亚稳态a³F_3,4上。通过近共振跃迁对处于a³F_2,3,4态上的钛原子进行泵浦,观测到一系列钛原子的受激喇曼散射和受激辐射,并对所有谱线进行了认证。钛原子的受激喇曼散射的脉宽和时间分辨谱表明,紫外激光离解四氯化钛产生钛原子的过程非常迅速,估计所需时间≤1ns。 关键词：     

Multiphoton mass spectra of Xe2 molecules in the range of excited Xe*(6p, 5d) atoms

The (2 + 1) photoionization mass spectra of Xe₂ molecules are studied in a supersonic jet upon excitation by laser radiation in the energy range 80321.3–77821 cm^?1, corresponding to the dissociation of the Xe₂ molecule into atoms Xe(¹ S ₀) + Xe*(6p, 5d). Several vibrational progressions are observed, which are attributed to two-photon transitions of Xe₂ from the ground state to the excited states of the O ⁺ _g, 1_g, and 2_g symmetries. Based on the analysis of these progressions, the molecular constants of a number of excited states of Xe₂ are estimated.     

The quenching of Pb(6p 2 1 D 2) atoms in collisions with molecules

The collisions of metastable Pb(6p ^{2 1} D ₂) atoms with various molecules were studied by the diagnostics of radiation from a hollow cathode lamp and a laser on lead vapor. Experiments were performed for a gas flow of lead atoms with argon. The Pb(6p ^{2 1} D ₂) states were excited in a gas discharge in the presence of reagent gas molecules. The absolute rate constants for the quenching and chemical reactions of lead atoms in the ground and excited states were determined. The quantum efficiency of chemical reactions was close to one for the N₂O, CH₂Cl₂, SF₆, and CuBr molecules. Long-lived chemical compounds were formed in these reactions.     

Experimental investigations of the formation of XeF*(B 2II1/2) excimer molecules during the injection of SF6 into a xenon plasma flow

The luminescence of XeF*(B ²II_1/2) molecules from a zone formed in the injection of SF₆ gas into a freely flowing xenon plasma jet is investigated. The experiments show that both the energy characteristics of the luminescence and the geometrical dimensions of the plasmachemical reaction zone can be controlled by varying the power input to the plasmatron and the mass flow rates of SF₆ and the xenon plasma. It is shown that the main contribution to the production of XeF*(B ²II_1/2) excimer molecules under the given experimental conditions is from two-particle ion-ion reactions involving Xe ions and SF ₆ ⁻ and SF ₅ ⁻ molecular ions. Zh. Tekh. Fiz. 68, 36–42 (February 1998)     

A polarized CARS investigation of the fine structure population inversion of Cl atoms from laser photolysis of ICl and the quenching of Cl(2 P 1/2) by O2

The time resolved polarized CARS technique has been used to detect Cl atoms produced by photolysis of ICl in the presence and absence of O₂. A population inversion was observed between the ground state electronic levels Cl(² P _1/2) and Cl(² P _3/2). The rate constant for Cl(² P _1/2) decay (quenching + reaction) in ICl was determined to be (3.2±0.2)×10^–13 cm³/molecule×s; the rate constant for Cl(² P _3/2) reaction with ICl was determined to be (7.8±0.5)×10^–12 cm³/molecule×s; and the rate constant for Cl(² P _1/2) quenching by O₂ was determined to be (1.9±0.2)×10^–13 cm³/molecule×s.     

Influence of parameters of gas medium on the fluorescence of iodine molecules 129I2, 127I129I and 127I2 excited by semiconductor laser radiation

Calculated and experimental results of studies of the influence of vapor temperature of iodine molecules (¹²⁹I₂, ¹²⁷I¹²⁹I, and ¹²⁷I₂) and pressure of the analyzed medium on the intensity of fluorescence of the molecules excited by semiconductor laser radiation in the red spectrum region are reported. It is demonstrated that depending on the wavelength of laser radiation there exist different ranges of temperatures and pressure values at which the fluorescence intensities of each of the indicated iodine molecules reach their maximum values.     

Quenching of fluorescence from Na(32P) and K(42P) atoms following photodissociation of NaCl and KCl at 193 nm

 Quenching of fluorescence from Na(3² P) and K(4² P) atoms by various collision partners was studied at 973 and 1273K. Excited alkali atoms were produced photolytically by excimer laser light at 193nm. For each collision pair, the appropriate relative velocity was computed and used to evaluate the quenching cross-section from the measured rate constants. Cross sections for CO₂, O₂ and N₂ are large (10–60Ų) while for Ar, the values are <1 Ų. The results are compared with those of previous investigations as a function of relative velocity. Finally, implications for combustion diagnostics are briefly discussed. Received: 29 March 1996     

Optical resolution beyond the natural linewidth: A level-crossing experiment on the 32 P 3/2 level of sodium using a tunable dye laser

A level crossing experiment on the hyperfine structure of the 3² P _3/2 level of Na²³ was performed using a nitrogen laser pumped dye laser for the excitation of the Na atoms. The fluorescent light was observed in time intervals which were initiated up to seven lifetimes after excitation. Therefore the signal was only determined by atoms having survived in the excited state up to the initiating time. The minimum linewidth observed was 6 times smaller than the natural width. Neighbouring crossing signals, which overlap in a level crossing experiment using time integral observation of the fluorescent light, could be resolved. The accuracy of the hyperfine constants of the 3² P _3/2 level could be improved.