ZEKE spectra

Fig. 2.21. Comparison of PI, MATI and ZEKE spectra of pyrazine. Reproduced from Ref. [92] with permission. American Institute of Physics, 1991.

Figure 13. Comparison of experimental ZEKE spectra of NO+ [17] with ab initio calculated spectra [ 18] N/ reflects the initial rotational state of the transitions in the S intermediate state.

R. D. Levine To answer the question of Prof. Lorquet, let me say that the peaks in the ZEKE spectra correspond to the different energy states of the ion. From the beginning one was able to resolve vibrational states, and nowadays individual rotational states of polyatomics have also been resolved. The ZEKE spectrum is obtained by a (weak) electrical-field-induced ionization of a high Rydberg electron moving about the ion. The very structure of the spectrum appears to me to point to the appropriate zero-order description of the states before ionization as definite rovibrational states of the ionic core, each of which has its own Rydberg series. Such a zero-order description is inverse to the one we use at far lower energies where each electronic state has its own set of distinct rovibrational states, known as the Bom-Oppenheimer limit. 

D. Gauyacq I have a short comment on Prof. Schlag s remark on the multichannel quantum defect theory (MQDT) approach to ZEKE spectra The first ZEKE spectrum of NO was actually interpreted by using MQDT as early as 1987 [1]. In this work, a full calculation of the ZEKE peak intensities is carried out by the MQDT approach, which... 

E. W. Schlag That is a good point, although there are some other very profound intensity changes in anion-ZEKE spectra. 

L. Woste In stationary spectroscopy ZEKE certainly provides spectroscopic results at an impressive resolution. Using femtosecond pulses one can certainly not excite specific states as compared to ZEKE. The Fourier transform of the wavepacket evolution, however, exhibits also spectral resolution that easily reaches and even exceeds what we see in ZEKE spectra. For this reason, I do not see any disadvantage in using femtosecond NeNePo to probe states of a prepared molecule. 

This holds, in particular, for the asymmetric C—C stretching mode u16, also when determining D16 from ZEKE spectra [22], and leads to a reduced total JT stabilization energy when comparing with earlier work. 

Deviations from predicted rotational intensity distributions are very common in ZEKE spectra. This is due to random near coincidence between extremely numerous rapidly- and slowly-autoionizing resonances (Rydberg series converging to excited rovibronic states of the ion). Since the waiting time between excitation and pulsed field ionization is long, and the very weak DC and stray electric fields present during the ZEKE waiting period can induce weak interactions... 

Shape resonances are also responsible for intensity anomalies in the PES and ZEKE spectra of O2 (for example, Braunstein, et al, 1992). 

Cooper minima axe also responsible for non Franck-Condon vibrational intensity distributions and intensity anomalies observed in both PES and ZEKE spectra. As for atoms, when the photoionization transition corresponds to excitation from a Rydberg orbital having at least one radial node in its wavefunction, the... 

As noted in Section 8.1.2, numerous intensity anomalies are observed in ZEKE spectra. Most of them are due to autoionization. For the effects of rotational, vibrational, and electronic autoionizations, we refer to the work of Merkt and... 

The molecule is planar in its ground state. Bond lengths are obtained from theoretical calculations numbers in parentheses are derived from an alternative method of calculation. Franck-Condon calculation for NbsO and NbsO give excellent simulations of the experimental PFI-ZEKE spectra at 150 and 300 K. 

The major advantage of PFI-ZEKE is its energy resolution, which allows the resolution of rotational and vibrational structures of metal compounds.For example, the ZEKE spectra of vanadium dimers (V2) have a line width of 1.5cm (0.19meV), from which the rotational... 

Figure 3 ZEKE spectra of MNH3 (M = A1, Ga, In) and spectral simulations for indium adduct and insertion isomers (reproduced by permission of the American Chemical Society from J. Phys. Chem.

The analysis described above relies on the Franck-Condon principle and the changes in intensity of the ZEKE signal as the intermediate state level is changed. In this case, the data obtained from the spectra are more than sufficient to characterize the potentials however, intensity anomalies in ZEKE spectra are quite common and can make the interpretation difficult (see Section 18.4). 

ZEKE spectra,dissociation and MATI spectra,as well as studies on fluorescence d44 fragmentation dynamics. Many of these are dominated by vibronic effects which occur in a rich variety in this species. 

The 1 -h 2 photon study, via the valence B TIo state, extended the previous work. Long Franck-Condon progressions, arising from the valence character of the intermediate state, are evident in the ZEKE spectra of both spin-orbit components. In the lower spin-orbit component, the vibrational progression extends to at least = 62, and in the upper state as high as = 34. The spectrum in the range 75 000 to 80 000 cm of the lower spin-orbit state, which was recorded via v = 15, is shown in Figure 6. 

From the ZEKE spectra of hydrogen halides, the rotational-state distribution of the product ion provides a direct measure of the angular momentum of the outgoing electron this is a sensitive probe of ionization dynamics. Autoionization occurs very readily in these molecules, via rotational, vibrational and electronic pathways, and is often evident in the spectra recorded. A further motivation in much of the... 

The results were rationalized on the basis of the increasing number of autoionization decay channels that become available to the high-w Rydberg states as each ionization threshold is reached. An analysis of the decay-dependence of the ZEKE spectra via the E IA2 state provided evidence for a non-exponential decay of the high-n Rydberg states. 

Figure 9 ZEKE spectra recorded through various torsional levels of the Si state in toluene. The label EXC indicates the torsional transition to the intermediate So Si.

Weisshaar and co-workers recorded ZEKE spectra of toluene through different intermediate resonances of and they are presented in Figure 9. From the assignment it can be shown that there is a positive with lower in energy than the >a2 torsional state. The torsional states of the toluene cation (0, 15, 54 and 75 cm i) are not very different from the torsional states in the state (1,15, 55 and 77 cm i), leading to the conclusion that the torsional barriers in the cation and in are quite similar. 

Figure 12 The ZEKE spectra of l2-Ar recorded through the pn3/2]core 5d 2g state. (A) is through the overlapping (0%) vibrational levels, (B) the (3 o) levels and (C) the (S o) levels.

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