Anharmonic vibrational frequencies are essential tools for the detection and identification of molecules in astrochemical environments. Many molecules can be detected by rotational spectroscopy, but those without permanent dipole moments, such as the ubiquitous polycyclic aromatic hydrocarbons, can only be observed through vibrational spectroscopy. NASA missions like the ongoing Stratospheric Observatory for Infrared Astronomy (SOFIA) and the upcoming James Webb Space Telescope (JWST) offer a wealth of spectroscopic data, but experimental or theoretical values must be obtained here on Earth to elucidate specific molecules responsible for these spectral data. On the theoretical side, quartic force fields (QFFs) offer a solid compromise between computational efficiency and spectroscopic accuracy for predictions of fundamental frequencies, at least for relatively small molecules. For larger molecules, QFFs produced with gold-standard ab initio methods such as CCSD(T)-F12 are still too costly. As such, this talk will discuss routes for expanding the use of QFFs to larger molecules for which current methods have proven too costly.

Quartic force fields for the detection of molecules in space

ACS Spring 2022

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