ZEKE spectroscopy of the organometallic radicals MgCH3 and ZnCH3: Construction of a high-resolution "experimental" molecular orbital diagram

The resonance-enhanced multiphoton ionization (REMPI) and zero kinetic ener gy (ZEKE) photoelectron spectra of the organometallic radicals MgCH3 and Zn CH3 are reported. The radicals were generated in a pulsed supersonic expans ion and therefore had vibrational and rotational.temperatures of ca. 10 K. The REMPI experiments have resolved the spin-orbit and vibrational structur e of the excited state, which is used as an intermediate state in the ZEKE experiment. Because of the intrinsically high resolution of the ZEKE techni que, the photoelectron spectra of these radicals were vibrationally resolve d. We also report density functional calculations of the geometries and vib rational frequencies of these radicals, and those of the closely related ra dicals CaCH3 and CdCH3. We have shown how the photoelectron spectra of thes e radicals can be used to generate high-resolution "experimental" MO diagra ms of molecules that contain these fragments. We illustrate this approach w ith the MO diagram of Zn(CH3)(2).