math formatting

docs/6_bonds_and_spectra.md

@@ -314,12 +314,9 @@ The other atom then develops a dipole moment $\mathbf{p_2} = \chi \mathbf{E}$ wi
 
 The potential energy between between the two dipoles is
 
-\begin{align}
-U(r) &= \frac{-|\mathbf{p_1}||\mathbf{p_2}|}{4\pi\varepsilon_0 r^3}\\
-&= \frac{-|\mathbf{p_1}| \chi \mathbf{E}}{4\pi\varepsilon_0 r^3}\\
-&= \frac{-|\mathbf{p_1}|^2 \chi}{(4\pi\varepsilon_0 r^3)^2}\\
-&\propto \frac{1}{r^6}.
-\end{align}
+$$
+U(r) = \frac{-|\mathbf{p_1}||\mathbf{p_2}|}{4\pi\varepsilon_0 r^3} = \frac{-|\mathbf{p_1}| \chi \mathbf{E}}{4\pi\varepsilon_0 r^3} = \frac{-|\mathbf{p_1}|^2 \chi}{(4\pi\varepsilon_0 r^3)^2} \propto \frac{1}{r^6}.
+$$
 
 The dipole attraction is much weaker than the covalent bonds but drops slower with increasing distance.