# Molecular orbital diagram for CH2

I'm trying to draw an MO diagram for CH2 by mimicking this MO diagram (excluding the orbital images), but things don't look like the way I want it to be. I really want to make it nice and similar to the image, but what I'm doing right now just seems sad and would really appreciate it if someone can help me.

I tried using MOdiagram package, but needs A LOT of work on it, especially with the overall size of the diagram because it is too small when I typeset. So, it would be really nice if someone can help me. Please and thank you.

\documentclass{article}
\usepackage{modiagram}
\usepackage[version=4]{mhchem}
\begin{document}

\begin{MOdiagram}[labels-fs=\scriptsize]
\AO(1cm){s}[label={2s}]{0.5;}
\AO(-0.4cm){p}[label={2p}]{2;}
\node at (1cm, -1){C};
%%%%%%%%%%%%%%%%%%%%%%%
\AO(3cm){s}[label={$2\mathrm{a}_1$}]{0;pair}
\AO(3cm){s}[label={1e}]{0.9;pair}
\AO(3cm){s}{1.1;pair}
\AO(3cm){s}[label={$3\mathrm{a}_1$}]{2;pair}
\AO(3cm){s}[label={$4\mathrm{a}_1$}]{3;}
\AO(3cm){s}[label={2e}]{3.9;}
\AO(3cm){s}{4.1;}
\node at (3cm, -1){\ce{CH_2}};
%%%%%%%%%%%%%%%%%%%%%%%
\AO(5cm){s}[label={1s}]{2.5;}
\node at (5cm, -1){H};
\end{MOdiagram}

\end{document}

• Most likely \documentcalss{article} should be \documentclass{article}. And if I correct this, I get errors on my machine. Most likely you are not to blame for them but I am wondering which TeX installation you are using. – user121799 Mar 3 at 0:52
• @marmot Sorry for that. I tried fixing some details of it. See if the copy and paste works now, when you typeset. Please and thank you. – Dave2343 Mar 3 at 2:12
• Thanks for updating you MWE! Unfortunately I run into the issue tex.stackexchange.com/q/474476/121799 . (Anybody else having the same problem?) – user121799 Mar 3 at 2:24
• Try adding the package \usepackage[version=4]{mhchem} It should do the trick. @marmot – Dave2343 Mar 3 at 2:58

I haven't used MOdiagram before, but as you tagged the question , here is a (simple) pure TikZ solution.

I am not even using a chemistry package and writing BeH2 as BeH$_2$ :) but you really should change that in your document.

\documentclass[tikz,margin=3mm]{standalone}
\begin{document}
\begin{tikzpicture}
\draw[dotted] (-3,0)--(-.3,3)--(.3,3)--(4,-1)--(.3,-4.5)--(-.3,-4.5)--cycle;
\draw[dotted] (-3,-1.5)--(-.3,1.5)--(.3,1.5)--(4,-2)--(.3,-6.5)--(-.3,-6.5)--cycle;
\draw[thick] (-.3,3)--(.3,3) (-.3,1.5)--(.3,1.5) (-.8,0)--(-.2,0) (.2,0)--(.8,0) (-.3,-4.5)--(.3,-4.5) (-.3,-6.5)--(.3,-6.5) (-3,0)--(-3.6,0) node[midway,below] {$2p_z$} (-3.8,0)--(-4.4,0) node[midway,below] {$2p_y$} (-4.6,0)--(-5.2,0) node[midway,below] {$2p_x$} (-3,-1.5)--(-3.6,-1.5) node[midway,below] {$2s$} (4,-2)--(4.6,-2) node[midway,below] {$\Phi_\mathrm g$} (4,-1)--(4.6,-1) node[midway,below] {$\Phi_\mathrm u$};
\draw[dotted] (-4.6,0)--(1.9,0);
\draw (0,0) node[below] {$\pi_\mathrm u^\mathrm n$};
\draw (0,.75) node {$\sigma^*_\mathrm g$};
\draw (0,2.25) node {$\sigma^*_\mathrm u$};
\draw (0,-5.5) node {$\sigma_\mathrm u$};
\draw (0,-4.5) node {\rotatebox{90}{$\rightleftharpoons$}};
\draw (0,-6.5) node {\rotatebox{90}{$\rightleftharpoons$}};
\draw (0,-7) node {$\sigma_\mathrm g$};
\draw (-4.2,4) node {Be};
\draw (0,4) node {BeH$_2$};
\draw (4.2,4) node {2 H (\textsc{salc}s)};
\end{tikzpicture}
\end{document}