Photoelectron spectroscopy of Rydberg states of the methyl radical

Photoelectron spectra following two-photon resonant, three-photon ionization of CH3 and CD3 via selected vibronic levels of the 3pz and 4pz Rydberg states are reported. Because the 3pz and 4pz Rydberg orbitals are non-bonding, the geometries of the corresponding Rydberg states of CH3 and CD3 are similar to those of the ground states of CH3+ and CD3+, respectively. This results in nearly diagonal Franck–Condon factors, with the photoelectron spectra showing a strong propensity for the preservation of the vibrational state upon ionization. The results are compared with earlier studies of the photoelectron spectra of analogous Rydberg states of NH3.