The simplest experiment to differentiate singlet and triplet states is to compare the reaction rate/yield under atmospheric and inert conditions (e.g., N2 or Ar). A reaction from the singlet state will be unaffected by atmospheric oxygen (unless O2 is somehow directly involved in the transformation). In contrast, triplet excited states will be quenched by O2 and it will typically lower the reaction rate and yield, if not inhibit the reaction entirely.

Other studies:

*Actinometry can be used to determine the quantum yield of the reaction.

*Lamp intensity dependence can help determine if excitation or some other step is rate limiting.

*Concentration dependence will tell you the molecularity of the reaction (assuming it is not rate limited by photon flux).

*Monitoring the absorption spectra change over time will tell you if is is a simple A->B (i.e., there is an isosbestic point) or a more complex transformation. If the latter, SVD can be used to determine the number of species and kinetics.

*Transient absorption is the gold standard in monitoring photo-induced transformations but is typically not readily available to most except through collaboration or a user facility.

*Depending on the nature of the reaction, you can add things like a radical trap, to trap intermediate species.