Can super-excited molecules survive fragmentation?

Abstract

An Auger event triggered by electron-capture (EC) decay of 57 Co incorporated in a chelate molecule results in the loss of an average of 5 electrons. During subsequent charge neutralization, the molecule acquires >50 eV of excitation energy. Only molecules having a large π-electron system were found to escape fragmentation. The fate of the molecule was followed by the 14.4 keV Mossbauer emission which occurs 10-7 second after the EC event. For a conjugated molecule to survive fragmentation, it should be able to disperse its energy in a time interval shorter than the period of atomic vibrations. We had proposed earlier that p-electrons undergo collective excitation and that the plasmon decays in <10-14 second accompanied by ejection of an electron leaving the molecule unscathed. Intermolecular energy transfer is not important and even an isolated molecule of 57 Co(II) phthalocyanine encapsulated in a zeolite supercage escapes fragmentation following an Auger event. Our model for rapid disposal of large excitation energy receives additional support from recent reports of single or mulitphoton plasmon excitation (∼20 eV) in an isolated C60 and C70 fullerene molecule followed by ejection of a single energetic electron leaving the molecule intact.