LaTeX Forum

 \newsavebox{\myendhook} % for the tabulars
 \def\tagform@#1{{(\maketag@@@{\ignorespaces#1\unskip\@@italiccorr)}
 \makebox[0pt][r]{% after the equation number
 \makebox[0.4\textwidth][l]{\usebox{\myendhook}}%
 }%
 \global\sbox{\myendhook}{}% clear box content
 }}
 [ ... ]
 \sbox{\myendhook}{%
 \begin{footnotesize}%
 \begin{tabular}{@{}ll}
 $a_0$ & Bohrscher Radius ($\mathrm{= 0{,}53\,\mbox{\AA}}$)\\
 $e$ & Elementarladung\\
 $N_{si}$ & Anzahl der Siliziumatome\\
 & pro Einheitsvolumen\\
 $m$ & Atomgewicht\\
 $Z$ & Kernladungszahl
 \end{tabular}
 \end{footnotesize}}
 %
 \begin{equation}
 \varepsilon = \frac{E \cdot 4 \cdot \pi \cdot \varepsilon_{0}
 \cdot a_0 \cdot \left( Z_i^{\frac{2}{3}} + Z_{Si}^{\frac{2}{3}}
 \right)^{-\frac{1}{2}}} {Z_i \cdot Z_{Si} \cdot e2 \cdot \left( 1
 + \frac{m_i}{m_{Si}} \right)}\,;
 \end{equation}
 %
 \sbox{\myendhook}{abc}
 %
 \begin{equation} a2+b2=c2 \end{equation}
 %
 \begin{equation} z = 9 \end{equation}

\makebox[0.4\textwidth][r]{\usebox{\myendhook}}%