  The goal of this thesis is to calculate properties of D-Mesons with
QCD-Sum-Rules in order to understand the nature of D-Mesons with positive
parity. The result is that such D-Mesons most probably are Mesons with a four
quark rather than a two quark structure. In this thesis a spectral function
which contains two resonances is used to calculate the decay constants of the
first and the second resonance in the spectral function. Moreover, a
Breit-Wigner curve instead of a delta-function is used to approximate the peaks
of the resonances in the spectral function. The decay constants of the
resonaces corresponding to the second peak in the spectral functions have never
been calculated before.Also very practical problems are attacked, see the
paragraph about the misscalculation of D-Meson Sum-Rules. Another topic of this
thesis was the establishment of basical knowledge about QCD-Sum-Rules, the
Operator-Product-Expansion and Dispersion-Integrals. A discussion of these
topics and many explicite calculations are included.
