Theoretical Electronic and Rovibrational Studies for Anions of Interest to the DIBs

TL;DR

This paper uses advanced ab initio methods to study the electronic and vibrational properties of interstellar anions, identifying potential carriers for diffuse interstellar bands and aiding their detection in space.

Contribution

It provides detailed electronic excitation data for CH2CN- and similar anions, and predicts vibrational spectra to support astronomical detection efforts.

Findings

CH2CN- has a dipole-bound excited state linked to DIBs

19 other anions may have electronically excited states

Vibrational frequencies and spectroscopic constants predicted for detection

Abstract

The dipole-bound excited state of the methylene nitrile anion (CH2CN-) has been suggested as a candidate carrier for a diffuse interstellar band (DIB) at 803.8 nm. Its corresponding radical has been detected in the interstellar medium (ISM), making the existence for the anion possible. This work applies state-of-the-art ab initio methods such as coupled cluster theory to reproduce accurately the electronic excitations for CH2CN- and the similar methylene enolate anion, CH2CHO-. This same approach has been employed to indicate that 19 other anions may possess electronically excited states, five of which are valence in nature. Concurrently, in order to assist in the detection of these anions in the ISM, work has also been directed towards predicting vibrational frequencies and spectroscopic constants for these anions through the use of quartic force fields (QFFs). Theoretical rovibrational work on anions has thus far included studies of CH2CN-, C3H-, and is currently ongoing for similar systems.