Knowledge Bank

The electronic absorption spectrum of the $(0,2),(1,3)$, and (6,9) bands of the $B4\Sigma u--X4\Sigma g-$ system of $C2+$ was obtained using the velocity modulation technique in conjunction with heterodyne detection. The rotationally resolved spectrum shows perturbations, which are attributed to the $22\Pi u$ state. The mixing between the $B4\Sigma u-$ state and the $22\Pi u$ state for nearly degenerate levels generated enough intensity borrowing to observe twenty $22\Pi u\leftarrow X4\Sigma g-$ forbidden transitions. The bands, with their corresponding forbidden transitions, were fit to a model Hamiltonian. Line position measurements, line strength factors, and expectation values for the orbital angular momentum, $⟨\Lambda \prime ⟩$, for the forbidden transitions are reported. Molecular parameters from the global fit of each band, including their corresponding forbidden transitions, are reported.