  The elastic scattering, Stark transitions and Coulomb deexcitation of excited
antiprotonic hydrogen atom in collisions with hydrogenic atom have been studied
in the framework of the fully quantum-mechanical close-coupling method for the
first time. The total cross sections $\sigma_{nl \to n'l'}(E)$ and averaged on
the initial angular momentum $l$ cross sections $\sigma_{n\to n'}(E)$ have been
calculated for the initial states of $(\bar{p}p)_{n}$ atoms with the principal
quantum number $n=3 - 14 $ and at the relative energies $E=0.05 - 50$ eV. The
energy shifts of the $ns$ states due to the strong interaction and relativistic
effects are taken into account. Some of our results are compared with the
semiclassical calculations.
