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

Abstract

Spectra of the C₂⁻ B ²Σ_u⁺–X ²Σ_g⁺ 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 ²Π_u 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 T_e=4060±180, ω_e=1656±20, ω_ex_e=10.80±0.50, B_e=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 ²Π_u 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.