How do I move the underbrace out of the big parentheses while still keeping it underneath the term?
\begin{alignat*}{4}
& \frac{E_{0-0}}{hc} &&= C+\frac{E'(\upsilon'=0)}{hc} &\\
& &&= C+\frac{1}{hc}\left(\hbar\omega'_e\left(0+\frac{1}{2}\right)-\underbrace{\hbar\chi'\omega'_e\left(0+\frac{1}{2}\right)^2}_{\approx0}\right) & \quad\Big|\quad\parbox{9em}{\small{Vernachlässigung\\der Anharmonizität}}\\
& &&\approx C+\frac{\omega'_e}{4\pi c}
\end{alignat*}
Best Answer
I replaced
alignat*
with justalign*
as others also said and\Bigl,\Bigr
are also better. The\frac{1}{2}
looks unnecessarily big, so I used\tfrac
. Finally, to lower theunderbrace
you can add a virtual rule like\vphantom{\rule[-1em]{0pt}{0pt}}
noting that a\smash
is required to keep line spacing consistent.