  In this thesis, the QCD sum rules approach has been used to study the nature
of the following charmonium resonances: Y(3930), Y(4140), X(4350), Y(4260),
Y(4360) and Y(4660). There is a strong evidence that these states have
non-conventional (or exotic) hadronic structures since their respective masses
and decay channels observed experimentally are inconsistent with expected for a
conventional charmonium state. The same phenomenon occurs on the bottomonium
sector, where new states like Yb(10890) and Yb(11020) observed recently could
indicate the existence of new bottomonium exotic states. In this way, one
verifies that the Y(4140) state could be described as a D*sD*s (0++) molecular
state or even as a mixture of D*sD*s (0++) and D*D* (0++) molecular states. For
the Y(3930) and X(4350) states, both cannot be described as a D*D* (0++) and
D*sD*s0 (1-+), respectively. From the sum rule point of view, the Y(4660) state
could be described as a \psi' f0(980) molecular state. The extension to the
bottomonium sector is done in a straightforward way to demonstrate that the
\Upsilon' f0(980) molecular state is a good candidate for describing the
structure of the Yb(10890) state. In the following, one estimates the mass of
the exotic Bc-like molecular states using the sum rule approach, where these
new exotic states would correspond to bound states of D(*) and B(*) mesons. All
of these mass predictions could (or not) be checked in a near future
experiments at LHC. A large study using the Double Ratio of Sum Rules approach
has been evaluated for studying the heavy baryon masses in QCD. The obtained
results for the unobserved heavy baryons, with one (Qqq) and two (QQq) heavy
quarks will be an excellent test for the capability of the sum rule approach in
predicting their masses.
