A study of the core-electron X-ray photoelectron (X-p.e.) spectra of the f o compounds La, O, , LaMO, (M = Fe and Co), CeO,. and BaCeO, is described. Results on the chelate species [La(tmhd),] and [Ce(tmhd),] (tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) are included for comparison. Special precautions have been taken to ensure an optimal degree of surface purity of the samples. Satellite structure has been observed for the 4p. in addition to the 3d and 4d, signals in both the lanthanum(iii) and cerium(iv) compounds. These satellites are discussed in terms of coexcitations of the charge-transfer type, principally 0 2p + metal 4f transitions. In the cerium(1v) oxides the satellites are apparently due to energy-gain (representing ' shake-down ') rather than energy-

He(I), He(l1) and valence region X-ray photoelectron spectra are reported for the Group VIA hexacarbonyls and are assigned on the basis of published molecular orbital calculations. A pronounced increase in intensity of the first photoelectron band is observed on descending the group, and multiplet structure is clearly discernible on this band in the case of W(CO)6.As a starting point in the study of the U.V. photoelectron (pe.) spectra of transition metal complexes, the Group VIA hexacarbonyls are attractive in view of their high symmetry and volatility. The experience gained from an investigation of these molecules should provide a firm basis on which to develop an understanding of the u.v.-p.e. spectra of more complex systems containing the CO ligand. A preliminary report of the He(1) p.e. spectra has appeared but no detailed assignment was advanced.l Other ionisation studies of the Group VIA hexacarbonyls include electron impact work 2-5 and photoionisation,6* which yield only the first ionisation potential,? and also X-ray photoelectron studies primarily concerned with the core levels of the molecules. We report here the high resolution p.e. spectra of chromium, molybdenum and tungsten hexacarbonyls excited by He(1) radiation (58.4 nm). These show some significant differences from those previously reported. In addition, since assignment of these spectra depends to such a large extent on relative band intensities, we report the spectra excited by He(I1) radiation (30.4 nm) and also the valence region X-ray p.e. spectra. EXPERIMENTAL u.v.-p.e. spectra were recorded on a Perkin-Elmer PS 16 spectrometer modified by the inclusion of the Perkin-Elmer heated inlet system and a 2 mm bore boron nitride discharge capillary in the lamp unit. The use of this capillary, together with a low helium pressure and high current density (150 mA, 10 kV), gave approximately 10 % of the He(I1) line at 30.4 nm.This proved sufficient to give He(I1) spectra of satisfactory intensity (ca. 300 c/s). Efficient differential pumping on the lamp minimizes the intensity of the helium ionisation line at 24.58 eV, but the presence of this structure in low intensity is useful for calibration purposes.Early work is summarised in Part 1 of this ~e r i e s .~

Photoelectron spectra excited in the gas phase with He-I radiation are reported for the tetroxides, Ru04 and Os04, and for the oxychloride species V0Cl3, CrO2CI2 and Mo0,C12. The X-ray photoelectron spectrum of Os04 has also been measured. The nature of the metal-oxygen bonding in these molecules, as inferred from the spectrometric data, is discussed.We report here the results of a study by He-I photoelectron (PE) spectroscopy of the orbital electronic structures of the tetroxo-species RuO, and OsO,, and the oxychlorides VOC13, CrO,Cl, and MoO,CI, . This investigation represents a natural extension of our previous work on tetrahalide species such as TiC1, and VC14,1' but it was stimulated in part by the widespread interest 3-5 in the electronic structures of oxyanions such as MnO, , quasi-isoelectronic with RuO, and OsO,. He-I PE spectra of OsO, and RuO, have recently been reported by McGlynn and coworkersHowever, the results presented below show that both sets of spectra contain spurious structure due to impurities which, naturally enough, created some confusion with regard to the assignment of the spectra. and by Diemann and Muller.7 EXPERIMENTAL A N D RESULTSWith the exception of RuO, and MoO,Cl,, the compounds studied in the present work were obtained commercially and purified by standard procedures. Ruthenium tetroxide was prepared as a yellow solid of low melting point by the method of Berkowitz and R ~l a n d e r , ~ which involves the oxidation of RuC13 by bromate in aqueous solution. The product suffered slight contamination from bromine which was removed by partial distillation under reduced pressure. The sample was dried by means of a 4 A molecular sieve. Molybdyl chloride (MoO2Cl,) was prepared by chlorination of a commercial sample of MOO,. The pale yellow, microcrystalline product was purified by sublimation and finally obtained as lustrous orange needles, l o somewhat metallic in appearance. $The PE spectra shown in fig. 1 (a)-3 and 6-8 were measured on a medium resolution spectrometer using He-I (21.21 eV) exciting radiation. The spectra were calibrated by reference to lines due to admixed inert gases.

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The results of a study of the reduction of some platinum(1v) compounds during the course of X-ray photoelectron measurements are presented. All the compounds investigated suffered reduction though the observed rates varied considerably. Kinetic analysis of the peak intensities in the X-ray photoelectron spectra reveal that the reduction process is invariably first order, and a model is proposed to account for this finding. Platinum(I1) compounds studied were stable to X-radiation.