  We theoretically investigate internal conversion processes of a photoexcited
molecule in a condensed phase. The molecular system is described by
two-dimensional adiabatic ground and excited potential energy surfaces (PESs)
that are coupled to heat baths. We study the role of conical intersection (CI)
by computing the time evolution of wavepackets for the PESs both with and
without the CI. For this purpose, we employ the multi-state quantum
Fokker-Planck equation (MSQFPE) for a two-dimensional Wigner space. Numerically
integrating the MSQFPE, we investigated the time evolution of wavepackets for
the CI and avoided crossing (AC) models. We find that the calculated yields
through non-adiabatic transitions are sensitive to the profile of the PESs of
the CI model: Due to the vibrational motion in the coupling mode, the yield
depends on the distance between the CI point and the minimum point of the
adiabatic excited-state PES.
