Ultrahigh resolution spectroscopy of C2−: The A 2Πu state characterized by deperturbation methods

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Abstract
Spectra of the C2− B 2Σu+–X 2Σg+ transition have been obtained using a merged laser‐ion beam spectrometer with sub‐Doppler resolution. Strong perturbations of the B state by the previously unobserved A 2Πu state are analyzed to obtain the characteristics of the new state. The A state spectroscopic constants in wave numbers (with estimated standard errors) are found to be Te=4060±180, ωe=1656±20, ωexe=10.80±0.50, Be=1.630±0.005, and A=−24±1. All nine perturbations observed in this work and the five observed in the work of Herzberg and Lagerqvist are explained by the interaction of the A 2Πu state with the B state. These results, as well as the perturbation matrix elements, are compared with theoretical estimates and results for isoelectronic 13‐electron species.