Spherically confined H$_2^+$: $^2\Sigma_g^+$ and $^2\Sigma_u^+$ states

The molecular ion H$_2^+$ is studied under strong confinement conditions produced by a spherical barrier centered in the gravity center of the molecule. Results for the potential curves are obtained by diffusion Monte Carlo methods for the ground state (X$^2\Sigma_g^+$) and the first excited state (A$^2\Sigma_u^+$), and reported as functions of the internuclear distance d for different values of the confinement radius. Results show that the compressed state corresponding to both $^2\Sigma_g^+$ and $^2\Sigma_u^+$ present deep minima in their potential curves, due to the increased space for electron wave-functions when the protons are displaced from the barrier surface.