基本上，我尝试使用 amsmath 来对齐反应的两种可能结果，这自然不包含等号。
\begin{equation}
\ce{^{2}_{1}H} + \ce{^{2}_{1}H} &\rightarrow \ce{^{1}_{1}H} + \ce{^{3}_{1}H} + 4.03 \text{MeV}\\
&\rightarrow \ce{^{1}_{0}n} + \ce{^{3}_{2}He} + 3.27 \text{MeV}\\
\end{equation}
反应有一个分支，可能出现 2 种结果，我正在尝试对齐箭头。有什么建议吗？
答案1
您可以使用split或更精美的排版。
\documentclass{article}
\usepackage{amsmath,siunitx}
\usepackage[version=4]{mhchem}
\DeclareSIUnit{\eV}{eV}
\begin{document}
\begin{equation}
\begin{split}
\ce{^{2}_{1}H} + \ce{^{2}_{1}H}
&\rightarrow \ce{^{1}_{1}H} + \ce{^{3}_{1}H} + \SI{4.03}{\mega\eV} \\
&\rightarrow \ce{^{1}_{0}n} + \ce{^{3}_{2}He} + \SI{3.27}{\mega\eV}
\end{split}
\end{equation}
\begin{equation}
\ce{^{2}_{1}H} + \ce{^{2}_{1}H}
\mathrel{\begin{array}{@{}c@{}}\nearrow\\\searrow\end{array}}
\begin{array}{@{}l@{}}
\ce{^{1}_{1}H} + \ce{^{3}_{1}H} + \SI{4.03}{\mega\eV} \\[2ex]
\ce{^{1}_{0}n} + \ce{^{3}_{2}He} + \SI{3.27}{\mega\eV}
\end{array}
\end{equation}
\end{document}
甚至更高级的是tikz-cd：
\documentclass{article}
\usepackage{amsmath,siunitx}
\usepackage[version=4]{mhchem}
\usepackage{tikz-cd}
\DeclareSIUnit{\eV}{eV}
\begin{document}
\begin{equation}
\begin{tikzcd}[row sep=-1em,column sep=3em]
& \ce{^{1}_{1}H} + \ce{^{3}_{1}H} + \SI{4.03}{\mega\eV} \\
\ce{^{2}_{1}H} + \ce{^{2}_{1}H}
\arrow[ur,start anchor=real east,end anchor=west]
\arrow[dr,start anchor=real east,end anchor=real west] \\
& \ce{^{1}_{0}n} + \ce{^{3}_{2}He} + \SI{3.27}{\mega\eV}
\end{tikzcd}
\end{equation}
\end{document}
