Above-threshold detachment

The first applications of the SSEA to the multiphoton above-threshold detachment (ATD) spectra of the negative ion Li , to the ATI, HHG, and PADs in hydrogen, and in He were published in Refs. [54, 72, 73, 105, 119-123]. Additional types of applications are reviewed briefly in Section 6. 

D. M. Neumark We make no effort to produce vibrationally cold O2, since the B < — X transitions to predissociating upper state levels are rotationally resolved and completely understood. In the case of CH3O, we detach the CH3O- just above the detachment threshold so that we do not produce vibrationally excited CH3O. 

The continuous spectrum is also present, both in physical processes and in the quantum mechanical formalism, when an atomic (molecular) state is made to interact with an external electromagnetic field of appropriate frequency and strength. In conjunction with energy shifts, the normal processes involve ionization, or electron detachment, or molecular dissociation by absorption of one or more photons, or electron tunneling. Treated as stationary systems with time-independent atom - - field Hamiltonians, these problems are equivalent to the CESE scheme of a decaying state with a complex eigenvalue. For the treatment of the related MEPs, the implementation of the CESE approach has led to the state-specific, nonperturbative many-electron, many-photon (MEMP) theory [179-190] which was presented in Section 11. Its various applications include the ab initio calculation of properties from the interaction with electric and magnetic fields, of multiphoton above threshold ionization and detachment, of analysis of path interference in the ionization by di- and tri-chromatic ac-fields, of cross-sections for double electron photoionization and photodetachment, etc. 

It has also been demonstrated ( ), by studying the competition between electron loss and a unlmolecular decomposition of known activation energy, that sequential Infrared absorption continues to occur even after the anion has achieved enough total Internal energy to reach Its electron detachment threshold. This Implies that, near threshold, electron ejection must not be occurlng faster than the 10 -10 s photon absorption rate. These experiments do not, however, allow one to conclude with much certainty how far above... 

Figure 16 Schematic view of Sq -> Sj excitation in p-coumaric acid in its phenolate (a) or carboxylate (b) isomeric form. (Energies are given in electron volts.) In either case, the Sj state lies above the anion s adiabatic detachment threshold and is thus embedded in a continuum of electron-detached states. The core-excited rrrc resonance may be classified as a shape resonance (on the left) or a Feshbach resonance (on the right) depending on whether the low-lying continuum corresponds to detachment from the ir system (a" orbital) or from an a orbital that is not involved in the jr ir excitation. Adapted with permission from Ref. 186 copyright 2013 American Institute of Physics.

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