Zero-kinetic-energy photoelectron spectroscopy was used to measure the Franck—Condon factors for the carbon and nitrogen K-shell ionized states in N2 and CO. Corresponding features in the two spectra showed nearly identical energy spacings, both below and above the ionization threshold, as predicted by the equivalent-core model. The equilibrium bond length, Re, for the CO C-1s−1 state was determined to be 1.077±0.005 Å, and Re for the N2 N-1s−1 state was found to be 1.077±0.010 Å, changes of −0.051 Å for CO and −0.020 Å for N2 from their ground-state equilibrium bond lengths. The two-electron states corresponding to 1s−1 val−1π* were examined in the binding energy region predicted by Green function calculations. Two-electron states absent in the X-ray photoemission spectrum are present in both molecules and show evidence of vibrational structure.

Zero electron kinetic energy (ZEKE) photoemission was applied to examine the vibrational fine structure in the C 1s core line of methane. The line broadening from the post collision interaction (PCI) could be understood using the threshold lineshape of atomic argon. From a Franck-Condon analysis of the CH4 and CD4 ZEKE spectra, the geometry of core-ionized methane was evaluated. The equilibrium bond length was determined to be contracted by 0.052(7) Å from the ground state of methane (1.085 Å). Our results agree with the X-ray photoelectron spectroscopy experiment of Gelius, showing in addition that the molecular structure determined from the vibrational structure in core-level photoemission does not depend on the photoelectron kinetic energy.

Lately a variety of techniques have studied the electron correlation satellites with binding energies between the Ar 3s ionization potential (29.24 eV) and the lowest 2p−2 ionization potential (43.38 eV). One of these techniques, threshold photoelectron spectroscopy, with ≈90 meV electron resolution, revealed at least 25 Individual electronic states. All of these could contribute to any other satellite spectrum, and this observation helped explain some discrepancies between previous measurements. This technique has been applied here to the same region (30 eV ⩽ Hv ⩽ 45 eV) with higher resolution (<60 meV at the Ar 3s−1 peak). In this higher resolution spectrum at least 29 Individual electronic states are present. In some cases multiplet splitting Is observed.

The performance of a 55-meter Spherical Grating Monochromator (SGM) is described. A resolution of 60 meV has been achieved at 400eV, inferred from the linewidths of the nitrogen 1s-π* resonance. A photon flux of 4 × 1010 photons/s has been observed at 440eV (and with 0.5 eV resolution). An initial experiment has studied the core-shell resonances of gas-phase ethylene, C2H4. Vibrational fine structure was resolved both for the carbon 1s-π* and carbon 1s-Rydberg excitations. Comparison with the vibrational frequencies of ground state ethylene implies that the ν1 (C-H stretch) and ν2 (C-C stretch) or ν3 (H-C-H bend) are excited. It is suggested that the lower Rydberg orbitals, 3s and 3pσ, have molecular, anti-bonding character.

Resonant photoemission has been studied above the carbon 1s ionization thresholds in gas-phase benzene and ethylene. The experimental data for both molecules include relative partial cross section and asymmetry-parameter measurements for the C 1s main line and asymmetry-parameter measurements for one C 1s shake-up satellite in each system. Resonances above the C K edge have been analyzed on the basis of their decay to either the C 1s main line or valence-hole states, and have been tentatively assigned as either shape resonances or doubly excited states according to their observed one-electron or many-electron decay, respectively. The importance of determining the resonant behavior of all available photoemission channels in the proximity of a resonance is thus illustrated.

Zero kinetic energy (ZKE) spectra of N/sub 2/, CO, C/sub 2/H/sub 4/, and C/sub 6/H/sub 6/ were taken across the N1s (N/sub 2/) and C1s ionization thresholds. Discrete resonances at subthreshold photon energies were observed and were found to become more intense as threshold is approached relative to the same peaks in absorption spectra. For N/sub 2/ the satellite/main line branching ratios at threshold are: 11(1)% for the 419.7(1) eV binding energy satellite, and 2.3(1.0)% for the 426.5(1) eV binding energy satellite. For CO, the branching ratio for the 304.6(1) eV binding energy satellite is 15(2)% at its threshold. Branching ratios at threshold are also determined for the satellites of C/sub 6/H/sub 6/ and C/sub 2/H/sub 4/. Decay characteristics and assignments of the continuum features of C/sub 6/H/sub 6/ and C/sub 2/H/sub 4/ are also discussed.

Zero kinetic energy (ZKE) spectra of N2, CO, C2H4, and C6H6 were taken across the N1s (N2) and C1s ionization thresholds. Discrete resonances at subthreshold photon energies were observed and were found to become more intense as threshold is approached relative to the same peaks in absorption spectra. For N2 the satellite/main line branching ratios at threshold are: 11(1)% for the 419.7(1) eV binding energy satellite, and 2.3(1.0)% for the 426.5(1) eV binding energy satellite. For CO, the branching ratio for the 304.6(1) eV binding energy satellite is 15(2)% at its threshold. Branching ratios at threshold are also determined for the satellites of C6H6 and C2H4. Decay characteristics and assignments of the continuum features of C6H6 and C2H4 are also discussed.

The angular distribution for Ar 2p photoionization has been measured from just above threshold to 400 eV photon energy, and calculated in the same energy range using the relativistic random-phase approximation. The present experimental and theoretical results are in good agreement, but disagree somewhat with earlier Hartree-Fock (HF) calculations. The HF values are found to be significantly higher in the near-threshold region. Possible reasons for this discrepancy are discussed with relevance to the general understanding of inner-shell photoionization phenomena.

We report the photoionization partial cross section and asymmetry parameter in the 52–72 eV photon-energy range for the inner-valence orbitais (3t1u, 2eg, and 4a1g) in gaseous SF6. These results, combined with those for the (inner valence)/(outer valence) branching ratio, indicate resonant enhancement of the inner-valence levels at ≈ 59 eV photon energy which we associate with the 3t1u → eg shape resonance predicted by MSM Xα calculations.

Synchrotron radiation was used to excite an inner-shell electron into a Rydberg orbital at the Ar 2p to ns, nd, Kr 3d to np and Xe 4d to n p resonances. The resonant decay into shake-off channels was studied by three different electron measurements. Firstly, threshold electron scans were obtained over the resonances and thresholds. On the first resonance for each atom, photoelectron spectra were collected. The intensity distribution of low kinetic energy electrons was also determined for a few resonances. Finally, a shake calculation was carried out to compare with the experimental shake-off probabilities. Shake-off is observed to be a strong decay channel for these resonances.