L.O. Werme

Electron Spectroscopy of Open‐Shell Systems: Spectra of Ni(C5H5)2, Fe(C5H5)2, Mn(C5H5)2, and Cr(C5H5)2

The high resolution HeI electron spectra of Ni(C5H5)2, Fe(C5H5)2, Mn(C5H5)2, and Cr(C5H5)2 have been recorded and analyzed in terms of a molecular orbital description of the electronic structure. The ground state electronic configurations have been assigned by considering the feasible ground state configurations, determining the number and type of ionic states obtained from ionization of these configurations, and then comparing the predicted transitions with those observed experimentally. The ground state configuration and adiabatic first ionization potential of these molecules are: Cr(C5H5)2, ··· (e2g)3(a1g)1, 3E2g, I.P.=5.50 eV; Mn(C5H5)2, ··· (e2g)4 (a1g)1, 2A1g, I.P.=6.55 eV; Fe(C5H5)2, ··· (a1g)2 (e2g)4, 1A1g, I.P.=6.72; Ni(C5H5)2, ··· (a1g)2 (e2g)4 (e1g)2, 3A2g, I.P.=6.2 eV. Vibrational structure has been observed in the spectrum of ferrocene and is assigned to progressions in ν4, the symmetric ring‐metal stretching mode.

Analysis of vibrational structure and Jahn‐Teller effects in the electron spectrum of ammonia

The electron spectra of the 2A1←1A1 and the 2E←1A1 transitions of ammonia have been measured with sufficient resolution to observe considerable fine structure. The first transition, 2A1←1A1, contains two vibrational progressions which are assigned to the ν2 bending mode. The second transition 2E←1A1, consists of two overlapping electron bands due to Jahn‐Teller splitting of the 2E state. The vibronic structure accompanying this transition has been partially resolved and compared to the results of model calculations.

The Jahn-Teller Effect in the Electron Spectrum of Methane

The high resolution He I photoelectron spectrum of the (a12t25)2T2 < - (a12t26)1A1 transition in methane has been recorded and analyzed and a value has been obtained for the adiabataic ionization potential. The electron spectrum resulting from ionization of a t2 electron is a composite of at least three overlapping electronic bands which are separated by several tenths of an eV. These bands are the split components of the 2T2 electronic state of the CH4+ ion which is distorted by strong Jahn-Teller forces. The symmetry of the molecule in these three electronic states is believed to be, in order of increasing energy, D2d<C3e<D2h. The active vibration which causes the Jahn-Teller splitting is the r2(e) mode. The adiabatic ionization potential of methane is certainly below 12.62 eV. Our extrapolated value is approx- 12.51 eV. Four different vibrational progressions have been found, one of which shows vibronic splittings.

Electron Spectroscopic Investigation of Auger Processes in Bromine Substituted Methanes and Some Hydrocarbons

Auger spectra in gaseous CH4, CH3Br, CH2Br2, CHBr3, CBr4, C2H6, and C6H6 are excited by electron impact at about 5 keV energy and observed by means of a spherical electrostatic spectrometer at 90° to the primary electron beam. Besides the energies and the intensities of the Auger lines and the chemical shifts, the analysis of the spectra gives the energies and the lifetimes of the doubly ionized molecules. The line widths together with energy considerations indicate that some of these doubly ionized molecules rapidly dissociate. Comparisons are also made between the bromine and the carbon spectra.

The L2,3MM Auger Spectrum of Argon

The Ar L2,3MM Auger spectrum has been recorded. A great number of satellite lines are found many of which can be assigned to Auger transitions in doubly ionized argon. Several shake-up satellites are also found in the spectrum. The relative intensities of the spectral lines are given and the intensities are compared with previous experiments and calculations.

The high resolution electron spectra of thiophene, 2-bkomothiophene and 3-bromothiophene

The high resolution HeI photoelectron spectra of thiophene, 2-bromothiophene and 3-bromothiophene have been recorded and vibrational analysis has been obtained. The vibrational analysis has shown that Br-sensitive, ring-stretching and ring-bending modes are excited together in many of the bands, indicating the mixing of Br atomic orbitals with the ring. Very sharp bands are obtained from ionization of the Br “lone pair” electrons. Vibrational analysis coupled with extended Huckel calculations indicate that these “lone pair” electrons exist in two different orbitals, the out-of-plane a″ orbital and the in-plane a′ orbital. The a″ electrons are more strongly bonding than the a′ electrons because of the “back-bonding” ability of the a″ orbital. Comparison of the thiophene and bromothiophene spectra indicate an intensification of the bands resulting from ionization of ring π electrons with respect to those resulting from ionization of ring σ electrons in the heavier molecules. This observation facilitates identification of bands resulting from π and σ electrons and suggests further experiments to determine if it is a general phenomenon.

X-ray emission spectra of NH3 and N2O

The X-ray emission of NH3 and N2O are reported and the main X-ray transitions are identified. A correlation between nitrogen 1s binding energies obtained by electron and X-ray emission spectroscopy is given and differences between measured X-ray energies and X-ray energies calculated from electron spectroscopy are discussed.

X-ray emission spectra of small molecules

An instrument for X-ray emission studies of free molecules is described and electron and fluorescence excitations are discussed. The application of X-ray emission spectroscopy to free molecules is exemplified by the spectra of N2, CO, NO and CO2. From the spectra the core level binding energies of the molecules are deduced. For the diatomic molecules vibrational fine structure is resolved and analyzed in terms of different bond lengths in the initial and final states. The change in bond length, when the initial 1s vacancy is formed, is also discussed. The influence of the X-ray selection rules and molecular localization properties on the band intensities are discussed and exemplified by the O1s and C1s spectra of CO and CO2. In the spectra about ten satellites are found.

The Auger electron spectrum of carbon suboxide (C3O2)

Abstract The high resolution KLL Auger electron spectrum of carbon suboxide (C 3 O 2 ) in gas form, has been recorded. Assignments, assisted by intensity and energy calculations, are proposed for the peaks in the spectrum. A comparison is made with the oxygen Auger spectrum of CO. The ground state energy of the doubly charged C 3 O 2 ion is found to be 29.7 eV.

The carbon X-ray spectrum of gaseous CO

Abstract A new grazing incidence grating spectrometer for ultra soft X-rays from gaseous samples is briefly described. Threefold differential pumping makes direct electron impact excitation feasible. The carbon X-ray emission spectrum of CO is shown as a preliminary result.