Consider the following MWE
\documentclass[border=10 pt]{standalone}
\usepackage{mathtools,setspace}
\begin{document}
$\displaystyle
{\setstretch{1.5}
\begin{array}{ccccccccccccccccccccccc}
^{12} \mathrm{C}&+&^{1} \mathrm{H} &\longrightarrow& ^{13}\mathrm{N}&+&\gamma\\
&&&&^{13} \mathrm{N}& \longrightarrow&^{13} \mathrm{C}&+&e^{+}&+&\nu\\
&&&&&&^{13} \mathrm{C}&+&^{\mathrm{l}} \mathrm{H}& \longrightarrow&^{14} \mathrm{N}&+&\gamma\\
&&&&&&&&&&^{14} \mathrm{N}&+&^{\mathrm{l}} \mathrm{H}& \longrightarrow&^{15} \mathrm{O}&+&\gamma\\
&&&&&&&&&&&&&&^{15} \mathrm{O}& \longrightarrow&^{15} \mathrm{N}&+&e^{+}&+&\nu\\
&&&&&&&&&&&&&&&&^{15} \mathrm{N}&+&^{1} \mathrm{H} &\longrightarrow&^{12} \mathrm{C}&+&^{4} \mathrm{He}
\end{array}}
$
\end{document}
with the output
The output is pretty much what I'm looking for, but the way I get it seems rather clunky to me... Is there a better way to get the same output? The only relevant part here is that the same elements in each reaction need to be below each other... The spacing of the other parts doesn't have to be the same as in the picture..