Photoelectron imaging of CH−

The photoelectron images of CH− have been recorded using detachment wavelengths of 532 and 355 nm. The spectra show two features arising from photodetachment of the 3Σ− ground state of CH− to the ground, X2Π, and first excited, a4Σ−, states of CH. The electron affinity of CH is measured to be 1.26 ± 0.02 eV and the a4Σ− binding energy is 1.98 ± 0.02 eV. Photoelectron angular distributions depend on the detachment energy and are characteristic of electron ejection from two different, orthogonal, orbitals in CH−.