Long time stability of very high Rydberg states of vibrationally excited molecules

Experimental results which strongly indicate an extreme decoupling of the electronic from nuclear motions in very high Rydberg states of molecules are reported. The states detected for times as long as tens of μs after excitation are neutral even when there is enough energy to both ionize and fragment the molecule. The Born-Opppenheimer separation would lead one to expect strong coupling, at least when the electron is in the core region. The present results are discussed in light of other recent experiments on high Rydberg states and in terms of observation on electron-ion scattering.