Electron photodetachment from transient negative ions in the multiphoton ionization of CH3I

Abstract

Photoelectron spectra produced by the laser multiphoton ionization of CH₃I show a strong band due to absorption of an additional photon above the ionization threshold and resembling either inverse bremsstrahlung or ‘‘above threshold ionization.’’ The spectra are ascribed to a process of capture of Coulomb‐retarded photoelectrons to form transient CH₃I⁻ ions which are then photodetached before, during and after dissociation to CH₃+I⁻ products. Both CH⁻₃ and I⁻ ions are observed. Several aspects of the process are discussed in terms of a potential energy diagram.