Deuterium separation by ultraviolet laser dissociation of formaldehyde

Abstract

Irradiation of natural isotopic abundance formaldehyde with a narrow linewidth ultraviolet laser has yielded high deuterium enrichments (>600 at 5 Torr, 303 K) at five wavelengths in the range 340 to 355 nm. The temperature and pressure dependence have been measured for both the enrichment and the selectivity, the latter being determined from high resolution spectra of deuterated and natural formaldehyde. In general, for the conditions investigated (293–343 K; 2–26 Torr), both selectivity and enrichment are decreasing functions of temperature and pressure, but in certain cases the selectivity is independent of pressure over a small range. The highest enrichment (1110) was measured at 2 Torr, 293 K, 352.061 nm. The results can be explained in terms of hot bands as well as Doppler broadening and pressure broadening of formaldehyde absorption bands. For all five high enrichment wavelengths, the enrichment is larger than the selectivity at low pressure (<6 Torr), yet the two are equal at higher pressure. This implies that at low pressure the quenching of electronically excited HDCO by collisions with H2CO is a relatively inefficient process.