Photoionization channels

Note that m is an abbreviation for mf.) It can be seen that in general there exist two photoionization channels which differ in the orbital angular momentum ( of the photoelectron and can interfere. Equ. (2.9a) is the dipole selection rule for the... 

Figure 2.12 Radial integrals and phases for 2p photoionization in neon as functions of the kinetic energy of the photoelectron. The radial integrals R d2p and R s2p and the corresponding phases refer to the photoionization channels 2p - sd and 2p -> ss, respectively. Instead of the total phase 2p the individual contributions are shown (equ. (7.27)), namely the Coulomb phases <7ed2p and

In 2p photoionization in magnesium the partial cross section o2p is large compared to o3s and partial waves. Since Dd is larger than DS, it is essentially the Dd -amplitude which modifies the Ds -amplitude. This can be verified from Table 5.1 by comparing the RRPA results with those of the HFf P) calculation DS is increased while Dd remains nearly the same. 

The mixing coefficients are still unknown, but as will be seen below, in the present context only the a0-coefficient, where a0 < 1, is needed. Hence one can add to the wavefunction in equ. (5.26) the photoelectron s contribution, in order to calculate the matrix element between the initial state (equ. (5.24)) and the selected 2p photoionization channel. Working out the relevant dipole matrix elements, one then has the advantage that the overlap factors are unity if there the electron configurations are the same on both sides, and zero for all other cases. Hence only two ionization channels remain, and they are given by... 

In this general formulation no information is required concerning the underlying coupling scheme used for the description of the photoionization channels. 

The authors of [315] applied linearly polarized synchrotron radiation (45-66 nm) for ionization, which corresponds to photon energy from 18.76 eV (threshold) + 0.7 eV up to 27 eV. The measured V values, as dependent on photon energy, changed correspondingly from 0.052 down to approximately half the value, which made it possible to determine the value of r within the range 0.4-0.7. Further improvement of the experiment and refinement of the theoretical description was carried out in [179]. Accounting for the hyperfine and spin-rotational interaction effect made it possible to refine the photoionization channel relation r, which yielded values of 0.2-0.4 for photon energies between threshold and 32 eV. 

The contribution of Do(np-1 2P3/2 ed3/2 J = 1) then leads to intermediate coupling. In addition, >° (np-1 2P3/2 es1/2 J = 1) and the dots in equ. (8.41a) bring in further couplings in the continuum. In particular, the dots might stand for Dy(np l 2P1/2 e/y J = 1) and even for photoionization channels with active electrons from other shells where these contributions describe the important class of intershell couplings (see Section 5.2.4). Hence, equ. (8.41a) can also be written as (note i fy = e-1 2)... 

Fig. 5.15 Scheme to observe vibrational wavepacket dynamics through the conical intersection in NO2 (lower panel). Upper panel shows expected photoelectron energies from the four photoionization channels. (Reprinted with permission from Y. Arasaki et al., J. Chem. Phys. 132, 124307 (2010)). 

In interstellar regions subjected to fast shocks, the radiation field may have a very high intensity at 1215.6 A, because of recombination and collisional excitation of atomic hydrogen leading to Lyman a radiation (Hollenbach and McKee 1979 Neufeld and Dalgarno 1988). It is thus important to know whether a molecule has a photodissociation or photoionization channel at this wavelength. Molecules such as Hj, CO and Nj cannot be destroyed by Lyman a radiation, whereas other species like OH and H2O have cross sections of a few times 10 cm at 1215.6 A and are thus easily dissociated. Another strong peak in the radiation field in shocks is provided by the C III resonance line at 977 A. 

The photoionization of the amino acid tyrosine in alkaline solution was studied by CW TR EPR. The photoionization of deprotonated tyrosine leads to a spin-polarized emissive/absorptive CIDEP spectrum produced by the radical-pair mechanism, with the tyrosyl radical in emission and the solvated electron in absorption, which implies a triplet precursor. The exchange interaction J is found to be negative for this radical pair. The triplet photoionization channel is determined to be monophotonic. The singlet channel of the photoionization of deprotonated tyrosine is only seen upon the addition of the electron acceptor 2-bromo-2-methylpropionic acid (BMPA) to the sample. The singlet channel is isolated by performing TREPR on a sample containing tyrosine, BMPA and a triplet quencher (2,4-hexadienoic add). This channel is also found to be monophotonic. 

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