  Excited state hydrogen transfer (ESHT) is responsible to various
photochemical processes of aromatics including photoprotection of nuclear
basis. Its mechanism is explained by the internal conversion from aromatic
$\pi$$\pi$* to $\pi$$\sigma$* states via conical intersection. It means that
the electron is transferred to a diffuse Rydberg like $\sigma$* orbital apart
from the proton migration. This picture means the electron and the proton are
not move together and its dynamics are different in principle. Here, we have
applied the picosecond time-resolved near infrared (NIR) and infrared (IR)
spectroscopies to the phenol--(NH 3) 5 cluster, the bench mark system of ESHT,
and monitored the electron transfer and proton motion independently. The
electron transfer monitored by the NIR transition rises within 3 ps while the
overall H transfer detected by the IR absorption of NH vibration appears with
the lifetime of $\approx$20 ps. It clearly proves that the electron motion and
proton migration are decoupled. Such the difference of the time-evolutions
between the NIR absorption and the IR transition has not been detected in the
cluster with three ammonia molecules. We will report full of our observation
together with theoretical calculations of potential energy surfaces of
$\pi$$\pi$* and $\pi$$\sigma$* states, and will discuss the ESHT mechanism and
its cluster size-dependence between n = 3 and 5. It is suggested that the
presence and absence of a barrier in the proton transfer coordinate cause the
different dynamics. 2
