Ionization bands

Figure 9.5 f shows a ZEKE-PE specfmm of f, 4-difluorobenzene in which fhe firsf laser, of energy /zcvj, was timed to fhe Og band of fhe 5i-5o system. The second laser, of energy hcv2, was fhen timed across fhe M -fo-M ionization band system. 

Figure 1, The 8 ionization band (2B2g positive ion state) of Mo2(02CCHs)k fit with equally spaced symmetric vibrational components.

Figure 2. The relationship between the 8 ionization band and the potential wells of the ground state and the displaced 2Btg positive ion state.

I would like to make a few comments regarding the photoelectron spectra presented by Dr. Sattelberger. In referring to his spectrum of W2, he has assigned the ionization band... 

Therefore, ionization events occurring at lower I.P. appear more interesting since they involve the d-type metal-centered orbitals and correspond to the dn configurations in the ligand-field splitting patterns appropriate to the molecular symmetry of M(CO)n, Thus we have one ionization band with multiplet structure, at 7.52 and 7.88 eV, from the t%g configuration of octahedral V(CO)6 (21), one narrow band at 8.42 eV from in octahedral Cr(CO)6 (22), two bands of equal intensity at 8.60... 

Ionizations are evident before ligand ionizations with early transition metals Ti(m), V(III), or Cr(III), not evident at all or masked under ligand ionization bands with late transition metals such as Cu(ll) or Zn(II), and highly intermixed with the first ligand ionizations for intermediate transition metal configurations such as d6 of Co(III) or d6 of Ni(H). (Fig. 11). This type of behavior is probably of general occurrence and is in fact found also in other classes of coordination compounds, especially with sulfur ligands. 

The point of the identification of d-ionization bands in complex P.E. spectral patterns of coordination compounds lends itself to several empirical considerations. 

It should also be recalled that there are empirical checks which can be used for identification purposes first of all the increase in intensity of d-ionization bands often observed when He(II) is used instead of He(I) as the source of ionization. A more widespread use of such experimental aid is to be strongly recommended and will probably be one of the most fruitful experimental developments in this field. 

There are further possible advantages from the use of P.E. spectroscopy in the elucidation of the electronic structure of coordination compounds, and information not otherwise available or only indirectly available may thus come to light. The energy position of ionization bands of nonbonding orbitals, such as 6 s2 in (T1(I),... 

However, the first ionization bands in the PE spectra of these compounds (vertical IPs are n = 1 8.67 eV, n = 2 8.61 eV, n = 3 8.50 eV) show no apparent anomaly which might be ascribed to intramolecular n /it type CT interaction. This fact suggests that the CT interaction found by UV spectroscopy is weak and that the molecules are present in their open-chain forms under the experimental conditions employed for recording the PE spectra. 

FIGURE 5. The lowest energy ionization bands of nitromethane. The vibrational progressions are labelled. The argon lines are shown to the right. Reproduced by permission of the American Institute of Physics from Ref. 31... 

The complex [Cr(S2PF2)3] is volatile and monomeric in the gas phase.1002 Its He1 photoelectron spectrum has been reported.1038 The absence of interfering ionization bands of substituent groups outside the coordination sphere permitted detailed assignments. The UVPES spectrum of [Cr S2P(OEt)2 3] has been obtained,1039 and the symmetric v(Cr—S) vibration at 282 cm-1 has been identified in the RR spectrum of [Cr(S2PPh2)3].1040... 

The photoelectron spectrum of pyrrolidine in the low-energy (8-13 eV) region has been explored as part of a study of lone-pair ionization processes and an IP of 8.82 eV recorded for ionization from the N lone-pair. In A-methyl-3-pyrrolidinone the bands at 8.83, 9.53 and 12.24 eV have been assigned to ionization from the N lone-pair, the O lone-pair and the carbonyl 7r-system respectively. In 2-pyrrolidinone the first two bands are overlapped (at 9.53 and 9.76 eV), presumably a result of the amide resonance interaction, and on the basis of band appearance a reversed assignment to O lone-pair and N lone-pair ionization respectively has been proposed the 7rco ionization band is at 11.91 eV. Data are also available in the same paper for succinimide and its A-chloro and A-bromo derivatives (78MI30407). 

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