Broad band solar irradiation of gas- and liquid-phase 13CS2 produces polymers that are mass independently and mass dependently fractionated, respectively. The observed sulfur isotopic results differ significantly from those for 12CS2. Gas-phase photolysis of 12CS2 produces [12CS2] x that is fractionated in sulfur isotopes with δ34S = 45.85‰, δ33S = 28.31‰, and δ36S = 37.6‰, while liquid-phase photolysis yields [12CS] x fractionated in sulfur isotopes with δ34S = 32.48‰, δ33S = 16.98‰, and δ36S = 56.7‰. Gas-phase photolysis of 13CS2 produces [13CS2] x that is fractionated in sulfur isotopes with δ34S = 114.65‰, δ33S = 80.84‰, and δ36S = 168.7‰, while liquid-phase photolysis yields [13CS] x fractionated in sulfur isotopes with δ34S = 10.43‰, δ33S = 7.75‰, and δ36S = 22.4‰. The large effect that 13C enrichment has on the sulfur isotope distribution excludes a symmetry-dependent process as the origin for the mass-independent effect. Franck−Condon and vibronic coupling effects on nonradiative decay and intersystem crossing rates for the lowest excited states are suggested as the source of the mass-independent process. The absence of anomalous isotope effects for the materials prepared by liquid-phase photolysis support this proposal.

Irradiation of gaseous carbon disulfide [CS2(g)] at 313 nanometers produces a dark brown aerosol of (CS2)x. Its thermal decomposition products include disulfur (S2), carbon monosulfide (CS), and (CS)x. The photopolymerization process is accompanied by a large mass-independent isotopic fractionation of sulfur (a 5 to 10 per mil sulfur-33 excess and a 61 to 84 per mil sulfur-36 deficit). Excess sulfur-33 has been observed in several classes of meteorites. Photochemical production of (CS2)x may be important in the origin and evolution of cosmochemical environments such as the presolar nebula, meteorites, asteroids, and planetary atmospheres.