Effect of Mass-Independent Isotope Fractionation of Sulfur (Δ33S and Δ36S) during SO2 Photolysis in Experiments with a Broadband Light Source

This paper presents the results of experimental studies to examine the behavior of mass-independent isotope effects of sulfur Δ 33 S and Δ 36 S during photochemical processes initiated by broadband ultraviolet radiation. Experiments were performed in a flow photochemical reactor using a high pressure mercury lamp which is a source of radiation of a wide range with a maximum radiation intensity in the wavelength range 270−330 nm and weaker in the range 190−250 nm. We present measurements of the temperature and SO 2 pressure dependence of the sulfur isotope ratios in the elemental sulfur products. Based on a comparative analysis of our isotope data with data from previous experimental studies with xenon and hydrogen lamps, it was shown that the character of the correlation dependences between the values of δ 34 S, Δ 33 S and Δ 36 S in elemental sulfur depends on the relative spectral distribution of the radiation intensity. Based on a comparison of our isotope data with data from previous experimental studies with xenon and hydrogen lamps, it was shown that the character of the correlation dependencies between the values of δ 34 S, Δ 33 S and Δ 36 S in elemental sulfur depends on the relative spectral distribution of the radiation intensity. The results of our experiments allow the possibility that photochemical processes in the range 250−330 nm could play a significant role in the production of an isotope sulfur anomaly in the Archean atmosphere. The conditions in which radiation in the 250−330 nm region prevail over the radiation in the 190−220 nm region are consistent with the assumption that the level of solar radiation reaching the Earth’s surface in Archean was several orders of magnitude larger in the wavelength range 200−300 nm compared with the current level of radiation in this range.