Photochemical Separation of Mercury Isotopes. I. A Study of the Emission and Absorption Hyperfine Lines of Mercury at 2537 A

Abstract

An experimental and theoretical investigation has been made of the emission and absorption parameters in the excitation of Hg202 atoms in natural mercury to the 6(3P1) state by irradiation with the resonance line from an electrodeless discharge containing Hg202. The absorption has been studied as a function of (a) absorption path length, (b) the concentration of mercury in the absorption cell, (c) the pressure of certain foreign gases in the absorption cell, (d) the operating temperature of the lamp, and (e) the type of excitor used with the lamp. The results of the study show that for the unique formation of Hg2026(3P1) atoms in natural mercury it is necessary to use a well-cooled source operating at the minimum power level consistent with steady radiation output. Furthermore, the pressure of foreign gas in the absorption cell must be kept low to eliminate Lorentz broadening effects on the absorption hyperfine line. It has been found that the emission line from an electrodeless discharge operated at 26°C, and excited by a 2450 Mc oscillator, can be satisfactorily represented as a Doppler line modified by self-absorption. For the calculation of the frequency distribution of the emission line, the Doppler temperature of the emitting gas and the equilibrium temperature of the mercury in the lamp were taken as identical with the lamp wall temperature (26°C). The optical thickness of the path of self-absorption was evaluated from the dimensions of the lamp. It was found that the observed absorptions could be calculated directly from the ratio of the areas of the Doppler absorption line of the Hg202 atoms in the absorption cell to that of the self-absorbed emission line. The agreement between theory and experiment is taken as evidence that only Hg202 atoms are undergoing excitation under the defined conditions. During the investigation the cross sections for Lorentz broadening of hydrogen, methyl chloride and isopropyl chloride were determined with respect to the Hg202 absorption line. The values found were respectively 53.1, 192, and 297×10—16 cm2. This study was undertaken as a precursor to a systematic investigation of the reactions of various substrates with photo-excited mercury isotopes.