Laser Multiple-photon Dissociation Research Articles

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.

Observations on the spectral dependence andT/D isotope selectivity in the CO2 laser multiple-photon dissociation of trifluoromethane

Pulsed CO2 laser multiple-photon dissociation of CTF3 (v2 mode) bathed in argon and CDF3, CHF3 or CCl4 is examined as a function of laser wavelength (9.2–9.6 μm) and fluence. The dependence of the dissociation profile on wavelength is analyzed and comparisons are made to prior work. The single-stepT/D enrichment factor for infrared photolysis of trifluoromethane is measured; potential practical isotope separation is discussed. Pulsed infrared laser photolysis of CTF3 (v5 mode) using a 12 μm NH3 laser is also attempted.

Infrared laser multiple-photon dissociation of CTCl3: Wavelength dependence, collisional effects, and tritium/deuterium isotope selectivity

Isotopically selective infrared multiple-photon dissociation of CTCl3 in CDCl3 was investigated using a pulsed CO2 laser-pumped NH3 laser in the 12 μm region. The wavelength dependence of CTCl3 MPD in the ν4 absorption band was studied and the observed MPD peak was found to be shifted ∼10 cm−1 to the red of the absorption peak at 835 cm−1, consistent with the anharmonicity of the CTCl3 ν4 mode. The CTCl3 dissociation probability per pulse was investigated under various experimental conditions, including laser energy, pulse duration, and CDCl3 and buffer gas pressure. A rate equation model was used to analyze the CTCl3 experiments assuming various multiple-photon absorption and collisional relaxation mechanisms; this modeling effort was extended to a brief, more general, investigation of multiple-photon absorption by molecules with prespecified dissociation probability profiles. Lower limit single step T/D enrichment factors in chloroform MPD exceeding 15 000 were achieved under optimized conditions of the above parameters. No evidence of any CDCl3 depletion or decomposition product was observed in irradiated 200 ppm CTCl3/CDCl3 mixtures. CDCl3 absorption measurements were made using an optically pumped NH3 laser, and the observed high fluence T/D optical selectivity was found to be sufficiently high for practical tritium recovery.

Infrared laser multiple-photon dissociation of CDCl3 in a molecular beam

Pulsed CO2 laser multiple-photon dissociation of CDCl3 was examined in a molecular beam using 11 μ radiation. The only observed dissociation channel was hydrogen chloride elimination (≳99.1%), with no evidence of simple chlorine atom cleavage (<0.9%). Implications for isotope separation are discussed.

Tritium separation by laser multiple-photon dissociation of CDTCl 2/CD 2Cl 2 mixture

Selective multiple-photon dissociation of CDTCl 2 in CD 2Cl 2 was studied using a TEA CO 2 laser. The dissociation rate of CDTCl 2 had a maximum value at 927 cm −1 (P (38) line) irradiation. The frequency agreed with the calculated ν 7 vibrational frequency (929 cm −1) of CDTCl 2 within the accuracy of the calculation. The tritium enrichment factor β prod was obtained to be 29 −15 +156 at 3 Torr total pressure and at 907.8 cm −1 irradiation.

Two-frequency CO 2 laser multiple-photon dissociation and dynamics of excited state absorption in CDF 3

The two-frequency multiple-photon dissociation probability in CDF 3 is studied as a function of wavelength, fluence and pulse separation using two pulsed CO 2 lasers. When the r 5 mode of CDF 3 is excited by an R(12), 10.3 μ prepulse, the probability for subsequent dissociation is approximately constant from 940 to at least 990 cm −1. A model of excited state absorption in CDF 3 is presented to help explain these results. Implications for deuterium separation are also discussed.

Advances in deuterium and tritium isotope separation by IR laser multiple-photon dissociation

Advances in deuterium and tritium isotope separation by IR laser multiple-photon dissociation

ChemInform Abstract: INFRARED SPECTRUM OF TRIFLUOROMETHANE‐T AND IMPLICATIONS TOWARD TRITIUM ISOTOPE SEPARATION BY INFRARED LASER MULTIPLE‐PHOTON DISSOCIATION OF HALOGENATED METHANES

The infrared absorption spectrum of nearly pure CTF/sub 3/ was measured and compared with the fundamental absorption frequencies calculated by using published CHF/sub 3/ and CDF/sub 3/ general harmonic force fields. The agreement between calculated and observed frequencies is found to be satisfactory. On the basis of calculated and measured absorption frequencies, photochemical separation of T from H is very attractive in trifluoromethane when using CO/sub 2/ laser multiple-photon dissociation near the strong CTF/sub 3/ ..nu../sub 2/ band centered at 1077.0 cm/sup -1/. Photochemical separation of both T from H and T from D is attractive when using a CO laser near the strong CTF/sub 3/ ..nu../sub 1/ band centered at 1930.3 cm/sup -1/.

Infrared spectrum of trifluoromethane-t and implications toward tritium isotope separation by infrared laser multiple-photon dissociation of halogenated methanes

The infrared absorption spectrum of nearly pure CTF/sub 3/ was measured and compared with the fundamental absorption frequencies calculated by using published CHF/sub 3/ and CDF/sub 3/ general harmonic force fields. The agreement between calculated and observed frequencies is found to be satisfactory. On the basis of calculated and measured absorption frequencies, photochemical separation of T from H is very attractive in trifluoromethane when using CO/sub 2/ laser multiple-photon dissociation near the strong CTF/sub 3/ ..nu../sub 2/ band centered at 1077.0 cm/sup -1/. Photochemical separation of both T from H and T from D is attractive when using a CO laser near the strong CTF/sub 3/ ..nu../sub 1/ band centered at 1930.3 cm/sup -1/.

Deuterium separation at high pressure by nanosecond CO2 laser multiple-photon dissociation

Photochemical deuterium separation is evaluated at pressures up to 1 atm using 2 ns duration CO2 laser pulses to achieve multiple-photon dissociation (MPD) as the isotopic separation step. Photochemical performance is compared for Freon 123 (2,2-dichloro-1,1,1-trifluoroethane), difluoromethane, and trifluoromethane based on deuterium optical selectivity in absorption, photoproduct yield, and single-step deuterium enrichment factor. The absorption coefficient versus energy fluence is measured from 0.01 to 3 J/cm2 fluence for CF3CDCl2, CDF3, and CHDF2; added buffer gas results in an order-of-magnitude increase in the CDF3 absorption coefficient. The deuterium optical selectivity in absorption at 0.5 J/cm2 fluence with added buffer is 80 for CF3CDCl2 at 10.65 μ, 800 for CHDF2 at 10.48 μ, and 2500 for CDF3 at 10.21 μ. The absorption coefficients and hence optical isotopic selectivities are dependent on fluence, and the optical selectivity attains a maximum value of 8000 for CDF3 below 0.01 J/cm2 fluence. The deuterium-bearing MPD photoproducts at high pressure are trifluoroethylene for Freon 123, hydrogen fluoride for trifluoromethane, and both hydrogen fluoride and monofluoroacetylene for difluoromethane. Yield data determined by gas chromatography are analyzed using a model describing MPD due to a focused Gaussian beam in an absorbing medium to remove compositional and geometrical effects; this analysis results in a saturation fluence (at which the dissociation probability approaches 100%) of 12±2 J/cm2 for CF3CDCl2, 20±2 J/cm2 for CDF3 buffered by 1 atm argon, 30±2 J/cm2 for CDF3 buffered by 60–400 Torr CHF3, and 22±3 J/cm2 for CHDF2 buffered by 100–400 Torr CH2F2. Near unity dissociation probabilities are obtained for samples unbuffered by argon with operating pressures up to 40 Torr for Freon 123, and up to 400 Torr for both difluoromethane and trifluoromethane; the methane derivatives are much more resistant to high pressure collisional quenching than Freon 123. The single-step deuterium enrichment factor is 1200±300 for natural isotopic abundance Freon 123 at 30–100 Torr (10.65 μ) determined by mass spectrometry of the main trifluoroethylene photoproduct. The single-step deuterium enrichment factor determined indirectly from gas chromatographic analysis is 2500±500 for natural difluoromethane at 200 Torr (10.54 μ), and 11, 000+4000−2000 for natural trifluoromethane at 100 Torr (10.21 μ). It is concluded that both difluoromethane and trifluoromethane are photochemically satisfactory for viable large-scale laser production of heavy water.

IR photolysis of CDF 3: a study in kinetics of multiple-photon dissociation with applications to deuterium separation

CO 2 laser multiple-photon dissociation (MPD) of CDF 3 is examined as a function of fluence and collisions, providing new understanding of MPD. Notably, the dissociation yield is increased 100-fold due to collisions with argon. Photochemically, this molecule is ideally suited for deuterium separation.