  We calculate ionization energies and fundamental vibrational transitions for
H$_2^+$, D$_2^+$, and HD$^+$ molecular ions. The NRQED expansion for the energy
in terms of the fine structure constant $\alpha$ is used. Previous calculations
of orders $m\alpha^6$ and $m\alpha^7$ are improved by including second-order
contributions due to the vibrational motion of nuclei. Furthermore, we evaluate
the largest corrections at the order $m\alpha^8$. That allows to reduce the
fractional uncertainty to the level of $7\cdot10^{-12}$ for fundamental
transitions and to $4\cdot10^{-12}$ for the ionization energies.
