Relativistic and QED corrections to the 2pσ_(u)(upsilon = 1) vibrational state of the H⁺₂ molecular ion

Relativistic and QED corrections to the recently discovered first vibrational $2p\sigma_u$ state are presented. This state has an extremely small nonrelativistic binding energy $E_B=1.085045252(1)\times10^{-9}$ a.u. Its wave functions has a maximum at $R\approx100$ a.u. and extends up to several hundreds. It is shown that this state does not disappear if higher order relativistic and QED corrections, including the Casimir--Polder effect, are taken into account.