  The long-searched C-H stretches of the fundamental ions CH$^+$ and
$^{13}$CH$^+$ have been observed for the first time in the laboratory. For
this, the state-dependent attachment of He atoms to these ions at cryogenic
temperatures has been exploited to obtain high-resolution rovibrational data.
In addition, the lowest rotational transitions of CH$^+$, $^{13}$CH$^+$ and
CD$^+$ have been revisited and their rest frequency values improved
substantially.
