Broad band solar irradiation of gas- and liquid-phase (CS2)-C-13 produces polymers that are mass independently and mass dependently fractionated, respectively. The observed sulfur isotopic results differ significantly from those for (CS2)-C-12. Gas-phase photolysis of (CS2)-C-12 produces [(CS2)-C-12](x) that is fractionated in sulfur isotopes with delta(34)S = 45.85 parts per thousand, delta(33)S = 28.31%, and delta(36)S = 37.6 parts per thousand, while liquid phase photolysis yields [(CS)-C-12](x) fractionated in sulfur isotopes with delta(34)S = 32.48 parts per thousand, delta(33)S = 16.98 parts per thousand, and delta(36)S = 56.7 parts per thousand. Gas-phase photolysis of (CS2)-C-13 produces [(CS2)-C-13](x) that is fractionated in sulfur isotopes with delta(34)S = 114.65 parts per thousand, delta(33)S = 80.84 parts per thousand, and delta(36)S = 168.7 parts per thousand, while liquid-phase photolysis yields [(CS)-C-13](x) fractionated in sulfur isotopes with delta(34)S = 10.43 parts per thousand, delta(33)S = 7.75 parts per thousand, and delta(36)S = 22.4 parts per thousand. The large effect that C-13 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.