The reactive flexibility of carbon and the unique physics of the interstellar medium (ISM) allow for the formation of dozens of terrestrially unstable species with rich and often dense spectra. Laboratory characterization of these molecules has led to the assignment of many lines with simulated line lists supplementing this data in conjunction with databases such as HITRAN. However, the majority of this research has focused on the ground and vibrationally excited state assignments with little regard to the contributions of electronically excited states. Our group has recently demonstrated the utility of an <i>ab initio</i> quartic force field (QFF) approach to predict the spectroscopic qualities of several small organic radicals and their associated anions. Equation-of-motion (EOM) coupled cluster (CC) methods allow for the formal description of electronically excited states while QFFs provide the highly accurate determination of anharmonic ro-vibrational reference data. Rotational constants, anharmonic vibrational frequencies, and zero-point geometries serve to complete the picture for difficult spectral assignments. Several test cases of this powerful combination are provided with the isoformyl (HOC) radical, a moiety seen in countless carbon-rich systems, serving as the initial benchmark against traditional CCSD(T) results. Low-lying excited states such as those from the first <sup>2</sup>Π state of the ethynyl (CCH) radical and potential dipole-bound excited states of the HOCO system are some of the challenges treated with this robust methodology.

Electronic excited states of interstellar species: Quantum chemical prediction of spectroscopic signatures using quartic force fields

249th National Meeting (2015)

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