Two-color Photoionization

Two-color photoionization through the triplet manifold has also been reported for biphenyl in aqueous micellar solution [80]. 

In the last few years, first measurements have been performed determining the length of the attosecond soft X-ray bunches. Paul et al. measured 250 attosecond pulses in a two-color photoionization experiment [5]. Making use of the fact that in a train of soft X-ray bunches the frequency spectrum consists of odd multiples ( harmonics ) of the frequency of the driver laser, they studied the ionization of Ar atoms by simultaneous photo-absorption from the soft X-ray bunch and the fundamental color of the femtosecond laser. Measured... 

The radical cation formed upon ionization of ANI has been studied by different spectrometric techniques, including photoelectron, two-color photoionization, ZEKE70,80,199,212-226 and mass107,227-232 spectrometries. In most cases, the technique used has been coupled with infrared spectroscopy, which allowed the fine vibrational spectrum of the ion to be determined, in both line position and intensity. For example, the ZEKE photoelectron spectrum216 was recorded by exciting to the neutral S ( 52) excited state, and well-resolved vibrational bands of the cation were observed. In conjunction with quantum chemical calculations of fundamental frequencies, an assignment of the observed vibrational bands can thus be made. A few theoretical studies56,107,218,233,234 have also been devoted to the radical cation. 

Kau Kaup, J.G., Breckenridge, W.H. Bond energies of CaAf, CaKr, and CaXe from resonant two-color photoionization thresholds, J. Chem. Phys. 107 (1997) 4451-4457. 

Ionization of the SiCl radical may produce the ground state of SiCl. Marijnissen and ter Meulen [96Mar] have measured the adiabatic ionization potentials IP of the two isotopomers Si Cl and Si Cl using (1+1) two-color photoionization efficiency spectroscopy (PIE). They started from the 2 =1/2 and Q = 3/2 spin-orbit components of the X II ground state of SiCl, with the following results ... 

MuUer-Dethlefs, K. Sander, M. Schlag, E.W. Two-Color Photoionization Resonance Spectroscopy of Nitric Oxide Complete Separation of Rotational Levels of Nitrosyl Ion at the Ionization Threshold. Chem. Phys. Lett. 1984, 112, 291-294. 

The photochemistry of Zn+—(CH4) and Zn —(CH3OH) complexes has been studied in detail In that context, the possibility of the formation of a metal-hydroxo insertion complex [HO—Zn—CH3]+ (the isomer of [Zn—(CH30H)]+) has also been discussed . In other series of studies, the mechanism of dimethylzinc zinc monoethyl cation, diethylzinc diethylzinc dimer and dipropylzinc photolysis has been investigated by photoionization techniques. It was the study of Borsella and Larciprete that first observed different gas phase photodissociation mechanisms for Mc2Zn and Et2Zn by using one- and two-color multiphoton ionization combined with TOE MS. 

The excitation profile for two-color 1+1 photoionization of 2,2 -bithiophene seeded in a supersonic helium expansion showed that its two-photon photoionization is significantly enhanced by resonance with the Si state, but the observed dynamics clearly show that the dominant channels for photoionization involve long-lived triplet state into which Si decays (94JPC4990). To fit the observed temporal profiles, sequential decay of Si through two triplet states must be invoked. 

Similar photoionization results were observed with 99 and 100 although picosecond (355 nm) and two-color measurements on 100 indicated that photo-... 

Although bond cleavage and photoionization are common processes occurring from upper excited states, the energy stored in these states can also facilitate the formation of new bonds. For example, multiphoton excitation of perylene and pyrene in cyclohexane leads to hydrogen abstraction from the solvent and subsequent radical coupling products [81]. Two-color irradiation of anthracene (47) in the presence of acrylonitrile leads to a four-fold increase in the amount of cycloadduct 101 as compared to that obtained under one-laser irradiation [52] (Scheme 7). That this is an upper triplet process was indicated by the triplet depletion... 

The nanosecond-picosecond two-color two-laser flash photolysis method is also useful to study the excited state of radicals, that is, the D, state. We applied nanosecond-picosecond two-color two-laser flash photolysis to detect the absorption and fluorescence spectra of the ketyl radical of benzophenone and its derivatives (BPH and BPDH ) in the excited state in the UV-visible region [111], since BPH and BPDH are well investigated radicals in various fields. Since BPH and BPDH are generated from irreversible ways, such as photoionization, we employed a streak camera to realize the single-shot detection of these intermediates. 

To our knowledge, 46 has never been observed in solution under stable conditions, even at low temperature. Pulse radiolysis " of benzyl chloride as well as flash photolysis ° of several derivatives in HHP have allowed the observation of the electronic absorption spectra of benzyl and its 4-methyl and 4-methoxy derivatives. The and NMR spectra of the 2,4,6-trimethylbenzyl cation and other more heavily substituted benzyl cations, however, have been studied at low temperature in superacid media. In the gas phase, cold benzyl radical has been probed by two-color, resonant two-photon ionization techniques, thus providing very accurate vibrational frequencies below 650 cm for the benzyl cation. Furthermore, the adiabatic ionization energy of benzyl radical and several isotopomers in the ground state were determined from their threshold photoionization spectra using resonant two-photon excitation and detection of electrons by pulsed field ionization. This information, combined with Af//° (CgH5CH2) from Ref. 212 leads to the value of Af//°m(46) reported in Table 9. 

S.-M. Wang, S.-L. Cong, K.-J. Yuan, Y.-Y. Niu, Photoionization of NO molecule in two-color femtosecond pulse laser fields, Chem. Phys. Lett. 417 (2006) 164. 

FIGURE 5.8 Schematic diagram of a ladder two-color PA experiment in Na2. The PA laser (red-detuned) is fixed on arovihrational level of either the singly-excited Ig or the 0 potential, while the photoionization (PI) laser (hlue-detuned) is scanned through the doubly-excited P3/2 + 3p3/2 asymptote. Ions produced by autoionization below this asymptote are due to excitation of doubly-excited states. (From Amehnk, A. et al., Phys. Rev. A, 61, 042707, 2000. With permission.)... 

As a fundamental study on field induced chemical reactions, Neidel and Vrakking et al. observed attosecond d3mamics of electrons in a series of small- and medium sized neutral molecules by monitoring time-dependent variation of the parent molecular ion 3delds [296]. The information on electron dynamics was extracted from experimental data on the basis of the relation between the time dependent dipole and ionization. This was performed in the two-color femtosecond near infrared (NIR) pump-attosecond extreme ultraviolet (XUV) probe experiment. They claim that the time-dependent dipole induced by the moderately strong NIR pulse field is monitored with attosecond time resolution. The oscillations are interpreted in terms of a time dependent screening induced by the polarization of the molecule, which alters the photoionization yield of the neutral molecule. This scheme can be considered as the first example of molecular attosecond Stark spectroscopy. 

Double photoionization spectra from TPEsCO are simple one-axis graphs, but complete data sets from double photoionization are inherently three-dimensional intensity as a function of two electron energies. Presentation is in the form of two-axis maps, with grayscale or color points to indicate intensity, or by projection into normal spectra of intensity against a single variable. Many choices of axes are possible, and different authors prefer... 

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