Doublet-quartet conversion in negative ions as a possible mechanism of the electron autodetachment delay

Molecular negative ions with abnormally high lifetimes (20 micros) relative to electron autodetachment were registered at 1.65 eV electron energy in pyromellitic acid imide by means of negative ion mass spectrometry with resonant electron capture. Using quantum-chemical calculations, it was shown that the delay of the electron autodetachment may be caused by the conversion of an originally generated molecular ion-doublet into a molecular ion-quartet, as a result of intersystem crossing of the potential energy surfaces of these ions. It was noticed that the ion-quartet cannot decay rapidly into the molecule of the ground state because of the prohibition of the spin flip, which is similar to that for phosphorescence. It can also not decay into the parent triplets, because these triplets are higher in energy than the ion. As a whole, both prohibitions provide the observed effect of the high lifetime of the ions.