Sequential two-photon absorption and singlet–singlet energy pooling in thiophosgene vapor

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Abstract
Emission from the second excited singlet state of Cl2CS vapor has been monitored following excitation with a tightly focused, pulsed dye laser in the region of the ground state to first excited singlet and triplet absorption systems. Excitation in the triplet bands produces prompt fluorescence from S2 as a result of sequential two‐photon absorption, S0→hνT1→hνS2. Excitation in the bulk of the singlet bands produces no prompt fluorescence but does produce delayed fluorescence as a result of a bimolecular singlet–singlet energy pooling process, 2S1→S2+S0.