For gas phase organic molecules, ab initio composite methods exist that are able to predict accurate rovibrational spectra. Typically, fundamental vibrational frequencies can be obtained to within 1 cm-1 of known experimental values. However, the question remains as to whether a similar methodology can be developed for transition metal-bearing molecules due to issues like scalar relativistic considerations, static (or strong/multireference) correlation, inner/outer core correlation, and other considerations not typically considered in “black box” quartic force field (QFF) computations. Rovibrational spectroscopic properties have been computed for scandium and titanium dicarbide (ScC2 and TiC2). Overall, we find that complete basis set CCSD(T) QFFs may not always provide the same level of agreement with experiment for inorganic molecules that it does for organic molecules. While agreement between theory and experiment is exceptional for ScC2 and its isotopologues, the ground and low-lying excited electronic states of TiC2 exhibit vibronic coupling and experimental characterization of its pure rotational spectrum is incomplete. Overall, our findings will greatly enhance the knowledge of metal-carbon bonding for laboratory groups working in molecular astrochemistry and spectroscopy.

Rovibrational quartic force fields of scandium and titanium dicarbide

2019 Spring National Meeting

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