The photoexcitation of a thermal polyatomic molecule at room
temperature from a ground electronic state to an excited one is
accompanied by a nonequilibrium distribution of the internal energy
in the excited state. The nature of the excited state distribution -
whether hot or cold - may be controlled through the photoexcitation
frequency. The nascent distribution may have a profound effect on
unimolecular isomerization, internal conversion or electron transfer
rates in the excited state. These rates may be controlled through
the frequency and temporal properties of the photoexcitation pulse.
Conversely, measurement of the rates serves as a molecular
thermometer for the nascent distribution in the excited electronic
state. Examples to be discussed are recent experiments on the
stilbene system, model electron transfer reactions, benzene and
naphthalene. The recent criticism by Troe and coworkers of our
interpretationof the dynamics of the stilbene system will also be
addressed.