Electronically Excited States of Interstellar Anions

In the search for carriers of the diffuse interstellar bands (DIBs), a nearly ubiquitous, as-of-yet unattributed interstellar absorption spectrum, new theories are being proffered to explain this astronomical phenomenon. One of these is that rarely occurring excited states of anions may be responsible for some of these features. Using state-of-the-art quantum chemical techniques we examine nearly twenty anions for their excited state properties. Using two known species as benchmarks, nine new molecules about which little is known are shown to possess dipole-bound excited states while three of these (CH2SiN −, SiCCN−, and CCSiN−) are predicted by our methods to possess both dipole-bound and potentially even valence-bound excited states, an incredibly rare circumstance. These anions may yet hold significance for the chemistry of the interstellar medium and for the DIBs.