A model potential that includes both correlation and polarization effects is proposed for electron-molecule collisions. It is based, as suggested by 0 Connell and Lane, on a hybridization of local electron-gas theory for short distances and the asymptotic form of the polarization potential. It ls cncfgy 1ndcpcndcnt and vcfy s11Tlplc to apply, depcnd1ng only on thc I11oleculaf chafgc dens1ty and polarizabihties. The potential has been calculated for several molecules (H2, N2, CO2, HF, HCl, and CO); the crossing point between the correlation and polarization potentials 1s remarkably constant"averaging 0.96 CV. Application in scattering calculations for Hz and N2 yields very encourag-1ng fcsults.

Theoretical studies are reported of total and partial-channel photoexcitation and ionization cross sections in carbon dioxide. As in previously reported studies of discrete and continuum dipole spectra in diatomic (N"CO, O"F,) and polyatomic (H,O, H, CO, 0,) molecules in-this series, separated-channel static-exchange calculations of verticalelectronic transition energies and oscillator strengths and Stieltjes-Tchebycheff moment methods are employed in the development. Detailed comparisons are made of the static-exchange excitation and ionization spectra with photoabsorption, electron-impact excitation, and quantum-defect estimates of discrete transition energies and intensities, and with partial-channel photoionization cross sections obtained from fluorescence measurements and from tunable-source and te, 2e) photoelectron spectroscopy The sp. ectral characteristics of the various discrete series and continua are interpreted in terms of contributions from compact 2m"(n. *), 5o. (o~), and 4o. "(o. *) virtual valence orbitals, and from more diffuse discrete and continuum Rydberg orbitals. The 2m"(m~) orbital is found to contribute to discrete excitation series, whereas the So. (o.*) and 4o. "(o.) orbitals generally appear in the photoionization continua as resonancelike diabatic valence features. Good agreement obtains between the calculated discrete excitation series and the results of a recent analysis of the available spectroscopic data. The calculated outer-valenceshell (1m ')X 'II, (1n."')A 'II", (3o."')B'S"+, and (4o. ')C 'S+ partial-channel photoionization cross sections are in good accord with measured values, and clarify completely the origins of the various structures in the observed spectra. There is evidence, however, of coupling among scattering states associated with 1m, ' and 1m."' ionic channels, giving rise to moderate disagreement with tunable-source photoelectron and fluorescence measurements over a portion of the spectrum. In the inner-valence-shell region, the calculated 2a"' and 30 ' cross sections are in qualitative accord with the observed many-electron spectral intensities, and provide a basis for quantitative interpretation when combined with appropriate intensity-borrowing calculations. The calculated carbon and oxygen E-edge cross sections are in good agreement with available cross sections obtained from electron-impact and photoabsorption measurements. It is of particular interest to find the oxygen E-edge (lo. , ', 10"')cross section exhibits both the expected 5', (o.~) and 4o"(o.*) resonancelike features. Finally, comparisons are made throughout of the discrete and continuum spectra in carbon dioxide with the results of previously reported studies in CO and 0" and the origins of the similarities and differences in the cross sections in these cases are clarified.

Theoretical investigations of total and partial-channel photoabsorption cross sections in carbon monoxide are reported employing the Stieltjes-Tchebycheff (S-T) technique and separated-channel static-exchange calculations. Pseudospectra of discrete transition frequencies and oscillator strengths appropriate for individual excitations of each of the six occupied molecular orbitals are constructed using Hartree-Fock core functions and normalizable Gaussian orbitals to describe the photoexcited and ejected electrons. Use of relatively large basis sets of compact and diffuse functions insures the presence of appropriate discrete Rydberg states in the calculations and provides sufficiently dense pseudospectra for the determination of convergent photoionization cross sections from the S-T technique. The calculated discrete vertical electronic excitation spectra are in very good agreement with measured band positions and intensities, and the partial-channel photoionization cross sections are in correspondingly good accord with recent electron-electron (e,2e) coincidence, synchrotron-radiation, and line-source branching-ratio measurements. Predicted resonance features in the X, B, 02s-I, and carbon K-shell channels are in particularly good agreement with the positions and intensities in the measured cross sections. A modest discrepancy between experiment and theory in the A-channel cross section is tentatively attributed to channel-coupling mechanisms associated with opening of the 111' shell. The total vertical electronic S-T photoionization cross section for parent-ion production is in excellent agreement with recent electron-ion coincidence measurements. Comparisons are made between ionization processes in carbon monoxide and in the previously studied nitrogen molecule, and similarities and differences in the respective cross sections are clarified in terms of conventional molecular-orbital theory.

An extension of the adiabatic-nuclei approximation appropriate for electron collisions with polar molecules is discussed. The method will find most useful application, but is not restricted, to molecules with large permanent dipole moments. Treatment of molecules with small or negligible dipole moments but significant quadrupole moments and/or dipole polarizabilities is also within its purview. The essence of the method consists of extracting the effects of the long-range interactions from the usual adiabaticnuclei expressions, and reintroducing them in the laboratory frame in a self-consistent manner. The first Born approximation is the simplest, but not the only possible, vehicle for this approach. The method is closely related to the angular frame-transformation method. Illustrative applications are presented.