On the Extraction of Time Information From Energy‐Resolved Experiments

It is well known that in principle energy-resolved and time-resolved experimentsprovide complementary information. A few examples are reviewed where the timeevolution of rapidly relaxing molecular systems is or could be better studied byenergy-resolved experiments: (1) the evolution of a pair of resonances coupled witheach other through a set of continua, (2) an irreversible relaxation of the intermediatestate in the two-photon excitation of a polyatomic molecule, and (3) the derivation ofa “dissociation time” from the angular distribution of fragments from photodissociationby linearly polarized light. In the first case it is shown how all parameters necessaryfor a time-dependent description may be obtained from the measurement, as functionsof the excitation wavelength, of both the total absorption cross section across theresonances and the partial cross section for a single exit channel. In the last twocases the relevance of a description in terms of an “eigentime” of the molecule isdemonstrated.