  We extend the one pion exchange model at quark level to include the short
distance contributions coming from $\eta$, $\sigma$, $\rho$ and $\omega$
exchange. This formalism is applied to discuss the possible molecular states of
$D\bar{D}^{*}/\bar{D}D^{*}$, $B\bar{B}^{*}/\bar{B}B^{*}$, $DD^{*}$, $BB^{*}$,
the pseudoscalar-vector systems with $C=B=1$ and $C=-B=1$ respectively. The
"$\delta$ function" term contribution and the S-D mixing effects have been
taken into account. We find the conclusions reached after including the heavier
mesons exchange are qualitatively the same as those in the one pion exchange
model. The previous suggestion that $1^{++}$ $B\bar{B}^{*}/\bar{B}B^{*}$
molecule should exist, is confirmed in the one boson exchange model, whereas
$DD^{*}$ bound state should not exist. The $D\bar{D}^{*}/\bar{D}D^{*}$ system
can accomodate a $1^{++}$ molecule close to the threshold, the mixing between
the molecule and the conventional charmonium has to be considered to identify
this state with X(3872). For the $BB^{*}$ system, the pseudoscalar-vector
systems with $C=B=1$ and $C=-B=1$, near threshold molecular states may exist.
These bound states should be rather narrow, isospin is violated and the I=0
component is dominant. Experimental search channels for these states are
suggested.
