Isotope separation of oxygen-17, oxygen-18, carbon-13, and deuterium by ion laser induced formaldehyde photopredissociation

Abstract

Near ultraviolet photopredissociation of formaldehyde has been verified as a highly selective method for enrichment of the rare stable isotopes of oxygen, hydrogen, and carbon contained in this molecule. High resolution absorption spectra of rare-isotope-substituted fomaldehyde show coincidences to within the Doppler profile with strong ion laser transitions in Xeiii at 345 nm and Neii at 332 and 338 nm. By tuning each ion laser transition with an intracavity etalon, optimum enrichment of each isotope was selected by monitoring formaldehyde fluorescence. Oxygen-18 was enriched up to ninefold using natural neon lasing at 332.374 nm, while substituting Ne-22 permitted up to ninefold O-17 enrichment and 33-fold C-13 enrichment at 332.371 nm. Use of D2CO instead of H2CO permitted 44-fold O-18 and 27-fold O-17 enrichment. Hydrogen photoproducts showed 24-fold HD enrichment at 337.822 nm, 60-fold HD enrichment at 345.426 nm, and 180-fold D2 enrichment at 332.377 nm. Single vibronic level photolysis of HDCO shows greater than 90% molecular photoproducts at wavelengths longer than 330 nm and a sudden rise to greater than 50% radical photoproducts below 320 nm. Photopredissociation of D2CO at 332 nm yields less than 1% radical photoproducts. Isotope scrambling in HDCO is about 40% at 325 nm, but drops to less than 6% at 338 nm. Isotope scrambling is 24% for both C-13 and O-18 at 332 nm. Enrichment of deuterium, carbon-13, and oxygen-18 was carried out using formaldehyde with initial isotope composition ranging from natural abundance to 50% to yield photoproduct with up to 88% isotopic purity.