Computational chemistry is uniquely suited to study molecules that are difficult to examine under laboratory conditions. Anions are one such class in which computer simulation enable deeper insights. Electronically excited states of anions are rare since most anions are only metastable, and analysis of such species in the laboratory is exceedingly difficult. Our group has pioneered a methodology for analyzing electronic states of anions. Dipole-bound states of anions are highly-diffuse associations of an extra electron interacting with the dipole moment of the core neutral. Excitation into this orbital takes place right at the limit of the electron affinity. We have clearly shown that vertically excited states computed with EOM-CCSD and increasingly diffuse even-tempered basis sets of the n-aug-cc-pVXZ type, where n spans from non-aug to t-aug, delineate between valence and dipole-bound states. Significant decrease in the excitation energy highlights a dipole-bound state, while little change in the energy indicates a valence excited state. Recently, we have also shown that the computational cost of this procedure can be reduced with the inclusion of s-type molecule-centered functions (MCFs). Our work has discovered ten small anions that posses the rare valence excited singlet state. Additionally, the use of MCFs has opened up the study of valence excited states to much larger systems including nitrogenated polycyclic aromatic hydrocarbon derivative anions where valence excited states are also found. The novel use of computation to examine electronically excited states of anions, especially valence excited states, will open deeper understanding of the underlying chemical physics.

Anions and computation: A match made in chemical heaven

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.