Multiphoton Isotope-Selective Dissociation of Formic Acid Molecules under Action of a Free Electron Laser

Abstract

The infrared multiphoton dissociation (IR MPD) of formic acid molecules (HCOOH → CO + H2O) with free electron laser radiation in the 3 μm region (C−H stretch vibrational absorption band) and in the 6 μm region (CO stretch vibrational absorption band) has been achieved using the same laser. Results indicate that initial excitation of this dimer is more efficient for MPD then initial monomer excitation. Carbon isotope-selective MPD has been performed with an isotopic mixture, H12COOH + H13COOH (50% + 50%), at an irradiating wavelength of 5.56 μm. For this mixture, isotopic selectivity s = k 12/k 13 = 23 has been attained as a ratio of the rate constants of the H12COOH MPD and the H13COOH MPD, respectively. The isotopic selectivity for 13C in the naturally occurring mixture (1.1% of 13C-containing molecules) s = k 13/k 12 = 22 has been attained at an irradiating wavelength of 5.90 μm.

Enrichment of Silicon Isotopes with Infrared Free-Electron Laser Radiation

“…Because of a variety of potential applications for isotopically pure silicon [1][2][3][4] and because of our previous photochemical experience 4 with Si 2 F 6 , we chose to conduct FEL isotope separation experiments with that species. Other research groups have determined that multiple-photon dissociation with an infrared FEL can be isotopically selective, resulting in significant enrichment of carbon [11][12][13][14][15][16][17] and nitrogen 18 isotopes.…”

Infrared Multiphoton Si Isotope Selective Dissociation of Phenyltrifluorosilane under Free Electron Laser Irradiation

“…Another way is to find a chemical that provides only molecular products as a primary result of IR MPD. For example, in the case of carbon isotopes separation, the chemical was found, that is, formic acid . Molecules (not radicals) are the primary products of IR MPD of formic acid molecules in gaseous phase under the action of FEL radiation.…”

“…For example, in the case of carbon isotopes separation, the chemical was found, that is, formic acid. 5 Molecules (not radicals) are the primary products of IR MPD of formic acid molecules in gaseous phase under the action of FEL radiation. It would be very interesting to find such a chemical for Si isotope separation as well.…”

“…On the other hand, the temporal, frequency, and spatial profiles of a FEL beam are different from ones for a TEA-CO 2 laser. Recently, it was demonstrated that multiphoton dissociation with an infrared FEL can be isotopically selective, resulting in significant enrichment of carbon, − nitrogen, and silicon isotopes.…”