THE ROVIBRONIC SPECTRA OF THE CYCLOPENTADIENYL RADICAL

Cyclopentadienyl (Cp) radical has been subject to numerous studies for the greater part of half a century. Experimental work has involved photo-electron spectroscopy,footnote{textsc{T. Ichino}, textit{et al. J. Chem. Phys.} 129, 084310 (2008)} laser induced fluorescence excitationfootnote{textsc{L. Yu, S. C. Foster, J. M. Williamson, M. C. Heaven and T. A. Miller} textit{J. Phys. Chem.} 92, 4263 (1988)} and emission,footnote{textsc{B. E. Applegate, A. J. Bezant and T. A. Miller} textit{J. Chem. Phys} 114, 4869 (2001)} infrared absorption spectroscopy,footnote{textsc{D. Leicht, M. Kaufmann, G. Schwaab, and M. Havenith}textit{ J. Chem. Phys. 145}, 7 (2016), 074304.}and recently rotationally resolved spectra in the CH stretch region taken at JILA. Even more theoretical works appear in the literature, but substantial advances in computation have occurred since their completion. Cp's highly symmetric ($D_{5h}$) structure and doubly degenerate electronic ground ($tilde{X}^2E_1^{primeprime}$), which is subject to linear Jahn-Teller distortion, have been a great motivation for work on it. We have commenced new computational work to obtain a broad understanding of the electronic, vibrational, and rotational, i.e. rovibronic, structure of the Cp radical as revealed by its spectra, with particular emphasis on the new infrared spectra. The goal is to guide experiments and their analyses and reconcile results from spectroscopy and quantum chemistry calculations