Scheibe-aggregates of Pseudoisocyanine in solution and in molecular monolayers

A new working molecule 1,1,1,3,3,3-hexafluoro-2-(trifluoromethyl)-propane-2-t (CF₃)₃CT, is reported for the isotope separation of tritium by TEA CO₂-laser-induced multiphoton dissociation (MPD). Selective and efficient dissociation of (CF₃)₃CT was observed by irradiation at about 980 cm^–1 where (CF₃)₃CH was nearly transparent. The critical fluence for dissociation of (CF₃)₃CT at 10R(28) 980.9 cm^–1 was estimated to be as low as 4.6 J/cm², which is the lowest of the tritiated halocarbons that we have ever reported. A detailed study was made of the pressure dependence of the dissociation rate constants for (CF₃)₃CT and (CF₃)₃CH to clarify the collisional effects in their MPD. The hydrogen isotope exchange between (CF₃)₃CH and HTO was found to be extremely rapid, which is advantageous in the practical laser separation cycle for tritium removal from water.     

Laser isotope separation of tritium from deuterium: CO2-laser-induced multiphoton dissociation of C2TF5 in C2DF5

Isotope separation of tritium from deuterium in heavy water was attempted by CO₂-laser-induced, highly-selective multiphoton dissociation of C₂TF₅ present in C₂DF₅. Single-step T/D separation factors exceeding 3000, 1000, and 500 were attained, respectively, for the first time with CO₂ laser 10P(34) 931.0 cm^?1 at 10, 20, and 30 Torr pentafluoroethane pressures at ?78 °C (i.e., equivalent to 15, 30, and 45 Torr at room temperature).     

ATP synthase: from single molecule to human bioenergetics

ATP synthase (F_oF₁) consists of an ATP-driven motor (F₁) and a H⁺-driven motor (F_o), which rotate in opposite directions. F_oF₁ reconstituted into a lipid membrane is capable of ATP synthesis driven by H⁺ flux. As the basic structures of F₁ (α₃β₃γδε) and F_o (ab₂c₁₀) are ubiquitous, stable thermophilic F_oF₁ (TF_oF₁) has been used to elucidate molecular mechanisms, while human F₁F_o (HF₁F_o) has been used to study biomedical significance. Among F₁s, only thermophilic F₁ (TF₁) can be analyzed simultaneously by reconstitution, crystallography, mutagenesis and nanotechnology for torque-driven ATP synthesis using elastic coupling mechanisms. In contrast to the single operon of TF_oF₁, HF_oF₁ is encoded by both nuclear DNA with introns and mitochondrial DNA. The regulatory mechanism, tissue specificity and physiopathology of HF_oF₁ were elucidated by proteomics, RNA interference, cytoplasts and transgenic mice. The ATP synthesized daily by HF_oF₁ is in the order of tens of kilograms, and is primarily controlled by the brain in response to fluctuations in activity.     

Infrared multiphoton dissociation of13CF3Cl induced by CO2 laser pulses

Selective infrared multiphoton dissociation of¹³CF₃Cl induced by CO₂ laser pulses adjusted on = 1071.9 cm^–1 has been studied in the energy rangeE between 0.5 and 2 J per laser pulse or fluence range between 5 and 25 J per cm², and in the pressure range between 0.10 and 60 Torr. The effect of these parameters on the isotopic selectivity of the dissociation gives information on the rotational relaxation constants. As for the dissociation probabilities, they vary exponentially withE ^–1. The applicability of such an Arrhenius-type relation is discussed and semi-quantitatively justified.     

Tritium isotope separation by CO2-laser irradiation at low temperatures

Tritium isotope separation by CO₂-laser induced multiphoton dissociation of CTF₃ is investigated. For the optimization of the performance of this working substance, trifluoromethane, the conditions to yield high-selectivity at high-operating pressure and low-critical fluence for complete dissociation are studied using our deconvolution procedure. The irradiation conditions are varied over the following ranges; wavenumber: 1052–1087 cm^–1, gas temperature: 25°C to –78°C, CHF₃ pressure: 5–205 Torr. The selectivities exceeding 10⁴ are observed for 85–205 Torr CHF₃ at –78°C by the irradiation at 1057 cm^–1.     

First-stage enrichment in CO2-laser-induced13C separation by a two-stage IRMPD process: IRMPD of CHClF2/Br2 mixtures

We have been studying the practical CO₂-laser-induced¹³C separation by a two-stage IRMPD process. The IRMPD of natural CHClF₂ in the presence of Br₂ mainly produced CBr₂F₂, which was found to be highly enriched with¹³C. The yield and¹³C-atom fraction of CBr₂F₂ were examined as functions of pulse number, laser line, laser fluence, total pressure, and Br₂ pressure using a CO₂ TEA laser with an output less than 1 J pulse^–1 in order to optimize experimental conditions for¹³C separation. For example, we obtained CBr₂F₂ at a¹³C concentration of 55% in the irradiation of the mixture of 100-Torr CHClF₂ and 10-Torr Br₂ with the laser radiation at a wavenumber of 1045.02 cm^–1 and at a fluence of 3.4 J cm^–2. The mechanism for the IRMPD is discussed on the basis of observed results. Using 8-J pulses, we were able to obtain 1.9×10^–4 g of¹³C-enriched CBr₂F₂ (¹³C-atom fraction, 47%) per pulse under selected conditions. It is possible to produce 90% or higher¹³C by the second-stage IRMPD of the CBr₂F₂ in the presence of oxygen.     

Efficient production of13C2F4 in the infrared laser photolysis of CHClF2

We report the isotopically selective decomposition of chlorodifluoromethane. Chlorodifluoromethane is used industrially in high volume for the production of tetrafluoroethylene and its polymers; thereby it is an attractive working substrate for a medium scale isotope separation process, both in terms of its price and availability.We have studied the infrared multiphoton decomposition of carbon-13 substituted chlorodifluoromethane molecules present at their natural abundance (1.11%). A well defined CO₂ laser pulse (80 ns FWHM) was used and both the yield of carbon-13 enriched product and the net absorption of laser radiation were measured. These measurements were made as a function of substrate pressure (10-800 Torr), CO₂ laser line (9P 12–9P 32) and fluence (2–8 J cm^–2) and were used to determine the energy expenditure per carbon atom produced () at specified product carbon-13 content in the range 30%–96%. The results of these parametric studies were interpreted in terms of the kinetics of multiphoton absorption and dissociation, and allowed an initial optimization of the experimental conditions to minimize .Optimum results were obtained at 1046.9 cm^–1, 69 cm^–1 to the red of the¹²CHClF₂ v ₉ band center. Irradiation of 100 Torr of chlorodifluoromethane at 3.5 J cm^–2 gave tetrafluoroethylene containing 50% carbon-13 for an absorption of 140 photons (0.017 keV) per carbon atom produced. This efficiency compares favourably with existing carbon-13 enrichment technologies and would require an absorption pathlength of only 2 m to absorb half the incident photons.Issued as NRCC 20112     

Efficient laser isotope separation of 13C using novel linear multi-pass cavity

¹³C isotope has been separated in the form of enriched product C₂F₄ by selective multi-photon dissociation (MPD) of Freon-22 (CHClF₂) using the 9P(26) laser line of a transversely excited atmospheric CO₂ laser. The non-linearity factor, γ, that determines the dependence of the yield of ¹³C isotope on the fluence (J/cm²) has been determined for various laser rotational lines (9P(20)–9P(26)) and the advantage of a lower γ in the case of 9P(26) is highlighted for macroscopic production of ¹³C isotope. It is also shown that a higher value of the optimum fluence at 9P(26) not only results in a higher enrichment efficiency but in a relatively lower value of γ also. The laser pulse energy is efficiently utilized for selective MPD of Freon-22 by focusing the pulse energy repeatedly with the help of a novel linear multi-pass cavity (LMPC). The novelty of this optical arrangement lies in its ability to maintain the laser fluence around an optimum value for a desired enrichment of ¹³C in the product. This also ensures a higher quantity of enriched product because of the higher reaction volume. The advantage of the LMPC over the conventionally used Herriott multi-pass cell has also been presented. The gain in reaction volume in the present optical cavity having 20 passes with a constant fluence in each pass is as high as 12. Isotope-selective MPD of Freon in a LMPC with constant fluence in each pass showed a distinct advantage in energy utilization to separate ¹³C isotope over the gradually reducing fluence case.This revised version was published online in August 2005 with a corrected cover date.     

X-ray preionized CO2 laser

A short pulse (100 ns) high-energy x-ray source has been used to preionize a transversely excited carbon dioxide gas discharge laser of 600 cm³ active volume. The maximum output power of 60 MW in a 50 ns FWHM pulse was achieved from a CO₂–N₂–He–CO–Xe static gas mixture at 600 Torr pressure. The energy conversion efficiency was 6%.     

Selective T/H separation by NH3 laser multiple-photon dissociation of CTCL3

The multiple-photon dissociation (MPD) of CTCL₃ and the selectivity of T/H separation were investigated using a pulsed NH₃ laser, whose radiation contained a few lines depending on operating conditions. When Xe was added to chloroform, the dissociation rate of CTCL₃ increased at chloroform pressures below 2 Torr as a consequence of the removal of multiple-photon absorption bottleneck by collisions with Xe. The dissociation rate of CTCl₃ decreased monotonically with increasing chloroform pressure from 0.2 to 7 Torr. The depletion of CHCl₃ was not observed within experimental errors. The lower limit of the tritium enrichment factor in photo-products produced by one pulse irradiation was 570 at chloroform pressure of 2 Torr.     

R branch tuning characteristics of the13CH3F Raman FIR laser

Summary We described a¹³CH₃F Raman laser pumped by a grating tuned 20 atmospheres CO₂ laser. The emission characteristics of the¹³CH₃F laser extends from 14 cm^–1–35 cm^–1 and from 49 cm^–1–72 cm^–1; about 65% of these frequency ranges can be covered with tunable radiation. The characteristics shows a strong dependence on the rotaional quantum numbers of the states involved in the Raman laser transitions and, within each tuning interval, on the frequency offset with respect to the frequencies of resonant transitions. We obtained, at 51 cm^–1, a maximum FIR laser pulse energy of about 800 J (at a pump energy of 200 mJ), corresponding to a photon conversion of about 8%. In some cases we have observed simultaneous emission at a Raman and a cascade frequency. In addition, FIR emission power dependence on¹³CH₃F gas pressure and pump pulse power were investigated for different J quantum numbers.     

Enrichment of 13C by IRMPD of CBr2F2

The CO₂-laser-induced infrared multiple photon decomposition of natural CBr₂F₂ in the presence of oxygen has been examined as a function of pulse number (30–1500), reactant pressures (CBr₂F₂, 10–150 Torr and O₂, 5–90 Torr), laser line [9P(8)–9P(32)], and laser fluence (1–3 J cm^–2) to optimize irradiation conditions for ¹³C-enrichment. CF₂O was the main carbon containing product and afterwards was converted into CO₂ via hydrolysis. A small amount of C₂Br₂F₄ was detected only under extreme conditions, for example, at high laser fluences or wavenumbers close to an absorption band. The ¹³C-atom fraction of the final product CO₂ was found to be 20–80%, depending on experimental conditions. The two-stage IRMPD process proposed previously has been examined in further detail in the present study. First, CBr₂F₂ containing about 30% of ¹³C was prepared in the ¹³C-selective IRMPD of natural CHClF₂ in the presence of Br₂. The second-stage IRMPD of the CBr₂F₂ in the presence of oxygen under selected conditions resulted in the high enrichment of ¹³C beyond 90%.     

Gain and saturation measurements in a discharge excited F2 laser using an oscillator amplifier configuration

The small-signal gain coefficient and the saturation intensity of a F₂ pulsed discharge molecular laser at 157 nm have been measured using two discharge devices in an oscillator-amplifier configuration. The small signal gain coefficient was measured to be 5.2±0.4% cm^–1 at 3 atm total pressure and 1.5 cm electrode spacing and 4.1±0.4% cm^–1 at 2 atm total pressure and 2 cm electrode spacing while the values of the saturation intensity were 5 MW/cm² and 4.6 MW/cm², respectively.     

Optical emission diagnostics of laser-induced plasma for diamond-like film deposition

Optical emission from a laser-induced plasma plume is recorded during KrF excimer laser ablation of graphite in a gas mixture of Ar and H₂ (3%) for deposition of diamond-like thin films. At sub-GW/cm² laser intensities the spectrum is dominated by the bands of C₂ and CN. From the band intensities, the vibrational temperatures of both radicals are calculated to be 12–15×10³ K, and their concentrations are estimated to be 5×10¹⁴ cm^–3 and 2×10¹⁴ cm^–3, respectively.     

Laser separation of oxygen isotopes by IR multiphoton dissociation of (CH3)2O

Isotopically selective (with respect to ¹⁸O) one- and two-frequency multiphoton dissociation of dimethyl ether (CH₃)₂O by pulsed TEA CO₂ laser radiation has been studied. The maximum primary selectivity, 16, is attained with the dissociation yields of the desired component (CH₃) ₂ ¹⁸ O ₁₈=5×10^–4 and 1.7×10^–2 for one- and two-frequency excitation, respectively. The dependences of MPD yields and selectivity on laser radiation frequency, (CH₃)₂O pressure, buffer gas (N₂) pressure and temperature have been measured. Multiphoton absorption coefficients have been measured and the average number of absorbed quanta calculated. The laser photon energy consumed for separating one ¹⁸O atom has been estimated: 11 and 4 keV/¹⁸O atom for one- and two-frequency excitation, respectively.     

TEA CO2 laser induced breakdown versus selective photochemistry in C2F5H and C2F5H/C2F5T mixtures

In the context of laser separation of tritium isotope using C₂F₅T in mixtures with C₂F₅H, we have studied the laser induced dielectric breakdown (LIDB) as a function of the system pressure using 10.6 μm radiation of a TEA CO₂ laser. By taking also into account our isotope selective results, we have found that LIDB does not imply difficulties by affecting the laser selective process. Analysis of the experimental results shows that LIDB works by cascade ionization and the recombination constitutes the major loss process. The LIDB threshold fluence Φ_th for the tritiated mixture was found to be lower than the corresponding value in pure C₂F₅H indicating preionization in the medium due to β emission of tritium.     

Absorption of CO 2 laser emission by freon-12

The infrared (IR) absorption of freon-12 (CF₂Cl₂) was studied in the emission range of a 3-W tunable CW CO₂ laser by using a brass cell with KBr windows that was located outside the laser resonator. The results show that CF₂Cl₂ absorbs all CO₂ laser emission lines in the ranges of 1073–1083 cm^-1 and 937–943 cm^-1. The most strongly absorbed laser line was 10P (28) ( 937.21 cm^-1). Absorption coefficient values were obtained for all available wavelengths of the CO₂ laser as the CF₂Cl₂ pressure was varied from 5 to 1000 mbar. By using the HITRAN database for freon-12, the absorption coefficients were calculated at the 10P (28) and 9R (28) lines as functions of the gas pressure and compared with the experimental values. The calculated results are in reasonable agreement with the experiment. PACS 33.20.Ea; 42.55.-f; 42.55.Lt     

Parametric study of the IRMPD of CF2HCl molecules with the 9P22 CO2 laser line

The separation of ¹³C by infrared multiple photon decomposition (IRMPD) of CF₂HCl has been parametrically studied in relation with some key parameters such as the laser fluence, the number of laser pulses, and the gas pressure. The process selectivity, the depletion of the ¹³C isotope in the residual gas, the relative amount of ¹³C separated per pulse, and the energy expenditure were determined as a function of the above mentioned parameters, and conclusions were drawn concerning the efficiency of the separation process. An isotopic selectivity of about 40 was obtained in the investigated range of pressure. At 10 Torr of pure CF₂HCl, the ¹³C depletion in the residual gas was 45% when only 300 laser pulses were used. A maximum amount of 4.6×10^–10 kg ¹³C separated per pulse was obtained.     

Sensitive intracavity photoacoustic measurements with a CO2 waveguide laser

A photoacoustic intracavity configuration is presented; a resonant photoacoustic cell excited in its first longitudinal mode is placed inside the cavity of a CO₂ waveguide laser. Due to the high laser power and the sharp intracavity focus, saturation effects occur in the excitation and relaxation process of absorbing C₂H₄ molecules. A more optimal configuration is applied to measure the C₂H₄ emission of several Rumex species. A detection sensitivity of 6 ppt (parts per trillion) C₂H₄ is reached, equivalent to a minimal detectable absorption of 1.8×10^–10 cm^–1.     

Selectivity enhancement in tritium isotope separation by multiple frequency multiple photon dissociation of the CTF3/CHF3 System

Isotope separation of tritium by multiple photon dissociation process in multiple frequency fields of a TEA-CO₂ laser is reported for the first time. A ten-fold improvement in the bulk selectivity was obtained in 8.5 Torr CTF₃/CHF₃ in the presence of buffer gas at room temperature using 9R(8) to 9R(14) CO₂ laser lines compared to single frequency excitation. Investigations of various process parameters such as exciting laser frequencies, pulse energy, sample and buffer gas pressure indicate that this is a promising technique for the separation of tritium.