Multiphoton detachment

Figure 1. One-color resonant multiphoton detachment spectra of C4, C6, and C8.

Figure 2. Time-of-flight photoelectron spectra of C. Top one-photon direct detachment with photon energy 4.66 eV. Bottom resonant multiphoton detachment with photon energy 2.04 eV. The electron affinity of linear C is 4.18 eV.

Figure 3. Electron emission time profiles from resonant multiphoton detachment of Cg at various photon energies. The lime width at full width at half maximum (FWHM) of the laser pulse is 30 ns.

Figure 4. Schematic drawing of Cg resonant multiphoton detachment mechanism for excitation at the band origin of the C2ng - Y2I1U transition (IC, internal conversion TE, thermionic emission).

The essentials of the SSEA for numerically compufed energy-normalized N-elecfron wavefunctions were published in 1994 by Mercouris ef al. [54], The firsf application was not only to the multiphoton ionization of H (whose specfrum is known exactly analytically), as a test case, but also to the multiphoton detachment of the four-electron Li negative ion, with two free channels, Li ls 2s S and ls 2p P°. Li (or Be) is the first system of fhe Periodic Table for which the proper description of the zero-order electronic structure requires a multiconfigurational Hartree-Fock (MCHF) description. In the context of the review of the SSEA, we also discuss briefly the formulation of the problem in terms of the full atom-EMF interaction,Vext(f), which is computationally convenient as well as necessary for certain problems involving, say, off-resonance coupling of Rydberg states, for which use of just the electric dipole term is inadequate [55-57]. 

In this section, we apply the Floquet-TDDFT approach with exterior complex scaling to the calculation of multiphoton detachment of Li in monochromatic linearly polarized laser field [28,64]. When applying a complex scaling transformation, a... 

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

Absorption of UV or visible light from a flash lamp or a laser is used to produce the solvated electron, too. Two photolytic processes may occur (1) the photon energy is sufficient to ionize a solute and produce the electron, for instance, photo-detachment from an anion (Cl , Fe(CN)g , Na ...) (2) the laser intensity is high enough to induce ionization of the solvent via multiphoton absorption (e.g. HjO -I- hv 112 + e ). For water, at least 8 eV is needed to ionize the solvent. 

Photoionization and Electron Detachment.—Photoelectron spectroscopy is not within the scope of this volume, but some papers on photoionization which may be of some interest are listed here. Several theoretical treatments of photoionization in atoms and small molecules have appeared.213 Photoionization in the rare gases,214 atomic hydrogen,215 alkali-metal and alkaline-earth atoms,21 magnesium atoms,217 group II atoms,218 mercury atoms,219 molecular hydrogen,220 several polyatomic molecules,221 and solvated electrons 222 has been discussed. Multiphoton ionization in the rare gases,223 benzene,224 and in molecular crystals has also been discussed.225 ... 

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. 

The multiphoton electron detachment from Li with photon energies ha> = 1.36 eV [54]... 

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. 

The first application of the SSEA to a many-electron system was to the TDMEP of the multiphoton electron detachment from the ground state of... 

Fig. 1.1. Principles of the real-time multiphoton ionization (MPI) (a) and NeNePo (b) spectroscopic technique, (a) Principle of time-resolved MPI spectroscopy. A wave packet is prepared in an excited state of the neutral system by a pump pulse. Since in general the transition probability to the ion state is a function of the wave packet s location on the potential-energy surface, the propagation of the wave packet can be probed by a second, time-delayed pulse, (b) Principle of the time-resolved NeNePo process. Starting in the anion s potential-energy surface, an ultrashort pump pulse detaches an electron cuid prepares a wave packet in the neutrcd. After a certain delay time At a probe pulse photoionizes the neutral. The time-dependent signal of the cation s intensity is detected. For convenience, this method is called NeNePo , Negative-to-Neutrcd-to-Positive...

Using a wavelength of 415 nm, the positive ions were mainly detected when there was a nonzero time delay between the pump and probe laser pulses, confirming that sequential processes of detachment and ionization are involved in the creation of the cations. Remarkably, more than 90% of the cluster cations were detected as trimers, showing that with ultrashort laser pulses, nonresonant multiphoton ionization with very little fragmentation is indeed possible. Nevertheless, small fragment peaks are detectable. 

McFarland, M.A. Marshall, A.G. Hendrickson, C.L. Nilsson, C.L. Fredman, P. Mansson, J.E. Stractural Characterization of the GMl Ganglioside by Infrared Multiphoton Dissociation, Electron Capture Dissociation, and Electron Detachment Dissociation Electrospray Ionization FT-ICR MS/MS. J. Am. Soc. Mass Spectrom. 2005,16,752-762. 

PES photoelectron spectrometer SF space focus L1-4 laser for different purposes LI resonant multiphoton ionization secondary ion excitation mass selective dissociation, electron detachment from anions anion formation, laser desorption TOF-sep mass separation by time-of-flight... 

McFarland, M. A. Marshall, A. G. Hendrickson, C. L. Nilsson, C. L. Fredman, P Mansson, J. E. Structural characterization of the GMl ganglioside by infrared multiphoton dissociation/electron capture dissociation, and electron detachment dissociation... 

Kalli, a. Hakansson, K. Preferential cleavage of S-S and C-S bonds in electron detachment dissociation and infrared multiphoton dissociation of disulfide-linked peptide anions. Int. J. Mass Spectrom. 2007, 263, 71-81. 

Wolff, J. J. Laremore, T. N. Busch, A. M. Linhardt, R. j. Amster, I. J. Influence of charge state and sodium cationization on the electron detachment dissociation and infrared multiphoton dissociation of glycosaminoglycan oligosaccharides. J.Am. Soc. Mass Spectrom. 2008, 19, 790-798. 

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