C. Willis

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 (ε) 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 ε.Optimum results were obtained at 1046.9 cm−1, 69 cm−1 to the red of the12CHClF2v9 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.

Enrichment of carbon-13 in the products of the multiphoton dissociation of CF3X Compounds

Abstract The separation factors for the enrichment of carbon-13 in the hexafluorcethane produced from the multiphoton dissociation of CF 3 I, CF 3 Br and CF 3 C1 are reported as a function of CO 2 -laser line. The bromide and chloride are significantly more selective than the iodide both at room temperature and at −50°C. This is a consequence of the spectroscopy of the individual molecules.

Isotopically selective multiphoton decomposition of CF3Br and CF3I: separation of selective and non-selective product sources☆

Abstract The decomposition yield and the isotopic selectivity of carbon-13 production in the infrared multiphoton decomposition of CF 3 Br and CF 3 I have been determined from the observed product C 2 F 6 . These two observables have been studied in focussed beam geometry as a function of accumulated number of pulses from the CO 2 laser, pressure of absorber and energy per pulse. The isotopic selectivity is independent of fluence but decreases with pressure, mostly due to equilibrium thermal processes. The amount of C 2 F 6 formed increases as a function of (pressure) 2 and of (pulse energy) 2 . This is explained in terms of a simple diffusional quenching model where energy pooling is the dominant reaction leading to dissociation.

Multiphoton decomposition of hexafluoroacetone: Effects of pressure, fluence, wavelength, and temperature on the decomposition yield and C‐13 and O‐18 isotopic selectivity

The yield and isotopic selectivity of the infrared multiphoton induced decomposition of hexafluoroacetone have been studied in both parallel and focused beam geometries as a function of temperature, pressure, fluence, and photolysing wavelength. At low conversions, the chemical stoichiometry of the decomposition process is simple, CF3COCF3    nhν    CO + 2CF3. Several potential interferences are discussed but it is concluded that the yield of CO directly reflects the yield of the primary dissociation event. Pressure effects are complex and not amenable to quantitative description, however, varying parameters such as fluence and photolysing wavelength lead to predictions which give a clear qualitative picture. In particular, it is possible to distinguish parametric variations due to spontaneous dissociation and dissociation dependent upon energy pooling. Isotopic selectivity provides a powerful insight in this area. Preliminary data on the effect of temperature have been obtained at constant incident fluen...

The decomposition of formic acid vapor by infrared radiation from a pulsed HF-laser

Abstract The decomposition of formic acid vapor by 2.783 μm infrared radiation from a pulsed HF laser has been studied at pressures from 1.6 to 44 torr temper

The selective decomposition of CF3 13COCF3 molecules at natural abundance: Multiphoton dissociation at threshold

The first example of a system is reported in which isotopic selectivity increases dramatically with increasing substrate pressure. Hexafluoroacetone is studied using infrared laser induced multiple photon decomposition. The parametric variations of pressure, laser frequency, and fluence to the reaction yield are reported. (AIP)

The decomposition of ethanol vapour by infrared radiation from a pulsed HF-laser

Abstract The decomposition of ethanol vapour induced by infrared radiation from a pulsed HF-laser has been studied as a function of pressure. At high pressures, above 10 torr, the main primary processes appear to be: C 2 H 5 OH → H 2 + CH 3 CHO, C 2 H 5 OH → C 2 H 4 + H 2 O, C 2 H 5 OH → CH 3 + CH 2 OH in a ratio of 3:2:1 which is independent of pressure. At low pressures the process yielding C 2 H 4 and H 2 O becomes dominant. The results suggest that the high pressure behaviour involves a “thermal” decomposition with collisional processes dominating, whereas at low pressures the decomposition is due to multiple photon absorption which at the lowest pressures approaches a collision-free unimolecular decomposition.

Infrared induced reactions in methanol-bromine mixtures: A negative result☆

Abstract Suggestions have been made that infrared induced reactions in CH 3 OH-Br 2 mixtures can lead to isotope separation. A careful quantitative study has been made of limiting quantum yields of the infrared induced reactions in such mixtures and they are found to be very low, φ ⩽ 10 −3 , both with radiation from a laser and from a black body source.

Viable Commercial Ventures Involving Laser Chemistry Production: Two Medium-Scale Processes

Consideration of viable commercial ventures involving laser chemistry must take into account not only the cost structure of the laser production step but must also consider all other steps in the venture through to provisions of goods or services to clients. Recent work on the two-stage infrared laser isotope separation of carbon-13 and the selective wavelength synthesis of vitamin-D is reviewed. The processes, which may be viewed as surrogates for direct carbon dioxide and excimer laser driven synthetic schemes, are discussed in terms of their technical description and the business opportunity they present.

The multiphoton dissociation spectrum of bis(perfluoroisopropyl) ketone

Abstract Multiphoton absorption and dissociation of bis(perfluoroisopropyl) ketone induced by a transversely excited atmospheric pressure CO 2 laser was studied as a function of the wavelength λ and the fluence F of the IR field. The molecule is almost uniquely suited to this type of study: its chemistry is simple allowing unambiguous actinometry and its adsorption spectrum is located at the centre of the 10P branch of the 13 CO 2 laser allowing the investigation of the full action spectrum. Both the probability P d (λ, F ) of dissociation and the average number 〈 n 〉(λ, F ) of photons absorbed per molecule were measured at constant pressure (0.5 Torr). The spectral dependence of P d at constant fluence is a single lorentzian function of halfwidth 5.8 cm −1 red shifted 6.0 cm −1 from the small signal IR absorption band. The peak for 〈 n 〉 is broader (full width at half-maximum of about 14 cm −1 ), asymmetric and red shifted by only 2.2 cm −1 .