Anomalously long-lived molecular negative ions of duroquinone.

The problem under investigation here is establishment of mechanisms of the resonant electron capture by molecules, using the example of duroquinone (2,3,5,6-tetramethyl-1,4-benzoquinone). A solution is important because it will provide new insights into the fundamental physical laws and widespread applications in various fields like molecular nanoelectronics, touched upon herein too. Resonant electron capture (REC) in duroquinone was studied with negative ion mass spectrometry of the REC as the main method, and UV absorption and the photoelectron spectroscopy as the auxiliary ones. The latter were used to study the electronic structures of the various neutral molecular states that are the parent ones for the negative molecular ions formed by electron attachment to the molecules. B3LYP/6-311 + G(d,p) calculations were widely used throughout the study. As a result, an intensive peak of the negative molecular ions with anomalously high lifetime (200 microseconds) was registered at the attached electron energy of 1.8 eV. The ions were determined to be quartets delaying the electron autodetachment because of spin prohibition and appearing via inter-system crossing from the negative molecular ion doublets produced in the core-excited Feshbach resonances. Finally, the pattern of the REC in duroquinone was obtained for the energy region of 1-4 eV which is presented by shape resonances, core-excited Feshbach resonances and by mechanisms little-known for molecules of inter-shell resonances and the formation of ion quartets. The latter were proposed to be related to the negative differential resistance in molecular nanoelectronics.