Shuji Kato

CO2 laser tritium isotope separation: Collisional effects in multiphoton dissociation of trifluoromethane

Multiphoton dissociation of ppm level CTF3 in CHF3 is reported. The effect of buffer gas pressure on the specific dissociation rates and the isotopic selectivity is investigated. Pulse energy dependence of the dissociation rates is converted to the intrinsic relation between the fractional conversion per pulse and the fluence by means of the new deconvolution technique. By addition of 100 Torr argon, the critical fluence of CTF3 was decreased from 136 to 34 J/cm2, while the intrinsic selectivity was increased from 34 to 580. In the absence of buffer gas argon, the fractional conversion per pulse exhibits two different pressure dependences. Unlike in the case below 15 Torr, the system shows strong pressure dependence and loss of the isotopic selectivity above 15 Torr. Possible application to the tritium removal process is also discussed.

CO2-laser isotope separation of tritium with pentafluoroethane-T (C2TF5)

Isotope separation of tritium by CO2 laser-induced multiphoton dissociation (MPD) of C2TF5 is reported for the first time. The MPD spectrum obtained for C2TF5 comprised a broad peak at about 940 cm−1 where C2HF5 was nearly transparent. The unimolecular dissociation of C2TF5 was induced with much lower laser fluence than that for CTF3, another working molecule we proposed for laser isotope separation of tritium. The mechanisms and kinetics of the dissociation of C2TF5 and C2HF5 were investigated under various experimental conditions: laser frequency, pulse energy, pulse duration, tritium concentration, sample pressure, buffer gas pressure and irradiation geometry. Single-step separation factors exceeding 500 were achieved with the most efficientP(20) line in 00o–10o0 transition at 944.2 cm−1.

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).

Laser isotope separation of heavy elements by infrared multiphoton dissociation of metal alkoxides

Abstract The molecular laser isotope separation (MLIS) of germanium and zirconium was investigated by TEA CO 2 laser-induced infrared multiphoton dissociation (IRMPD) of germanium tetramethoxide (Ge(OCH 3 ) 4 ) and zirconium tetra-tert-butoxide (Zr[OC(CH 3 ) 3 ] 4 ). Ge(OCH 3 ) 4 at 0.5 Torr was irradiated with a TEA CO 2 laser and the maximum of dissociation was observed around 1040 cm −1 . The critical fluence for the complete dissociation was found to be as low as 0.86 L/cm 2 near the optimum dissociation wavelength. A separation factor for 70 Ge with respect to 74 Ge was 1.8 by irradiation with the 9P(28) line (1039 cm −1 ) at room temperature. When 0.5 Torr of Zr[OC(CH 3 ) 3 ] 4 was irradiated at 80 °C with a TEA CO 2 laser, the dissociation maximum was found around 984 cm −1 . The critical fluence for the complete dissociation was estimated to be about 0.94 L/cm 2 near 984 cm −1 . Selective dissociation of specific Zr isotopes was not observed at 80 °C within the detection limit of mass spectrometer.

Accurate extraction of reaction probabilities in IR multiphoton dissociation by a focused Gaussian beam: an improved analytical method.

An improved analytical method has been developed to extract the dissociation probability from the raw data in infrared multiphoton dissociation with a Gaussian-profile beam using a focused irradiation geometry. The conventional analytical method based on the power-law model is shown to overestimate the dissociation yield by as much as 60% compared with that predicted by the newly developed analytical method based on the cumulative log-normal distribution model. The obtained analytical solution is well fitted bysimple algebraic expressions, which enable us to analyze the experimental data quickly and accurately without tedious iteration procedures.

Infrared Multiphoton Dissociation of CF3CHClF: Primary Dissociation and Secondary Photolysis

The dissociation yield and branching ratio in CO2 laser-induced infrared multiphoton dissociation (IRMPD) of CF3CHClF were investigated by irradiation at 9R(20) 1078.6 cm−1 under an unfocused irradiation geometry (0.75-2.3 J/cm2) and a mildly focused one (1.2-18 J/cm2). By using a Br2-scavenging technique, it was revealed that the primary dissociation of CF3CHClF proceeded mainly via three-centered HCl molecular elimination and C-Cl bond rupture, with minor contributions of C-C bond rupture and HF molecular elimination at higher fluences. The secondary photolysis of the primarily produced species during the laser pulse to yield CF2 and CClF carbenes depended strongly upon the laser fluence.

Isotopically selective infrared multiple-photon dissociation of MoF6 by a H2-raman laser

Infrared multiple-photon dissociation (IRMPD) of MoF6 has been investigated with a parallel beam of a para-H2 Raman laser newly developed by our group. MoF6 gas (2 Torr, natural abundance) was put into in a static cell cooled to −58℃ and was irradiated with the laser line at 728 cm−1. The critical fluence of 0.11 Jcm−2 for complete dissociation was determined by analysis with a Gaussian beam model. Irradiation at the lower frequency side (728 cm−1) of the MoF6 ν3 band enriched the lighter isotopes in the residue. A maximum value for selectivity of 1.1 was obtained.

CO2 laser isotope separation of tritium with heptafluoropropanes (CF3CF2CTF2 and CF3CTFCF3

Abstract Tritium isotope separation was attempted by laser-induced multiphoton dissociation (MPD) of tritiated heptafluoropropanes CF 3 CF 2 CTF 2 ( n -C 3 TF 7 ) and CF 3 CTFCF 3 ( i -C 3 TF 7 ) using a transversely excited atmospheric pressure CO 2 laser. The isotopically selective MPD of n -C 3 TF 7 was expected at frequencies below the 10 μm region. The MPD spectrum of i -C 3 TF 7 showed a maximum at about 1000 cm −1 where i -C 3 HF 7 was almost transparent. The dissociation rate constant and isotopic selectivity were studied as a function of the sample pressure, the temperature and the irradiation geometry. The critical fluence for dissociation of i -C 3 TF 7 was found to be as low as 9 J cm −2 at 10 R(30) (982.1 cm −1 ), which is lower than those for tritiated trifluoromethane (CTF 3 ) and pentafluoroethane (C 2 TF 5 ). High isotopic selectivities exceeding 1400 were attained with i -C 3 TF 7 - i C 3 HF 7 at 982.1 cm −1 . An extremely large hydrogen isotope exchange rate was observed between i -C 3 HF 7 and tritiated water. These results indicate that i -C 3 TF 7 can be used as one of the most promising molecules for laser isotope separation of tritium.

CO2 laser isotope separation of tritium with (CF3)3CT

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.

Infrared multiple-photon dissociation by an unfocused beam in an optically thick medium: an analytical method for reaction yields

Mathematical solutions are derived that, based on the power-law fluence dependence of dissociation probability, describe the reaction yields in infrared multiple-photon dissociation by an unfocused beam in an optically thick medium. Assuming linear absorption (Lambert-Beers law), we present solutions for both a transversely uniform and a Gaussian beam geometry. An exact solution under a nonlinear absorption condition is also presented for the uniform beam geometry. The critical fluence (?(c)), a characteristic parameter for the dissociation probability, is determined from reaction yields using the solutions. It is found that the value of ?(c) can be fairly accurately determined over a wide range of optical absorption (up to 90% absorption), even when the Lambert-Beer law of absorption is approximately used for analysis instead of the exact treatment of nonlinear absorption.