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.

Theoretical studies are reported of the complete dipole excitation and ionization spectrum in H 2 0 employing Franck-Condon and static-exchange approximations. Large Cartesian Gaussian basis sets are used to represent the required discrete and continuum electronic eigenfunctions at the ground-state equilibrium geometry, and previously devised moment-theory techniques are employed in constructing the continuum oscillator-strength densities from the calculated spectra. Detailed comparisons are made of the calculated excitation and ionization profiles with recent experimental photoabsorption studies and corresponding spectral assignments, electron impact-excitation cross sections, and dipole (e, 2e )/(e, e +ion) and synchrotronradiation studies of partial-channel photoionization cross sections. The various calculated excitation series in the outer-valence (lb 1 - B 2 partial-channel cross sections are found to be largely atomic-like and dominated by 2p-kd components, although the 2b 2 (u*) orbital gives rise to resonance-like contributions just above threshold in the 3a 1 --+kb 2 and lb 2 -+kb 2 channels. It is suggested that the latter transition couples with the underlying lb 1 -+kb 1 channel, accounting for a prominent feature in the recent high-resolution synchrotron-radiation measurements. When this feature is taken into account, the calculations of the three outer-valence channels are in excellent accord with recent synchrotron-radiation and dipole (e, 2e) photoionization cross-sectional measurements. The calculated innervalence (2al 1 ) cross section is also in excellent agreement with corresponding measured values, although proper account must be taken of the appropriate final-state configuration-mixing effects that give rise to a modest failure of the Koopmans approximation, and to the observed broad PES band, in this case. Finally, the origins of the various spectral features present in the measured Ia 1 oxygen K-edge electron energy-loss profile in H 2 0 are seen to be clarified fully by the present calculations.

We have measured the electron drift velocity, longitudinal diffusion coefficient, and ionization coefficient in tetrafluoroethene (C2F4). Using these data and the results of ab initio calculations of the elastic, momentum-transfer, and neutral-excitation cross sections, along with measurements of the partial ionization cross sections, we have performed a swarm analysis in order to construct a self-consistent set of electron impact cross sections for C2F4. The swarm analysis consists of solutions to Boltzmann’s equation for electrons in C2F4 for values of E/N⩽500 Td and direct Monte Carlo simulation of electron transport in C2F4 for 500 Td⩽E/N⩽2000 Td. We present an analysis and discussion of the sensitivity of cross sections derived from swarm data to uncertainties in the electron transport measurements. We also discuss the failure of the two-term spherical harmonic solution to Boltzmann’s equation for E/N>500 Td, which necessitated the use of Monte Carlo simulations for high values of E/N.

Theoretical investigations of total and partial-channel photoabsorption cross sections in molecular formaldehyde are reported employing the Stieltjes-Tchebycheff (s-T) technique and separated-channel static-exchange (!YO) calculations. Vertical one-electron dipole spectra for the 2b 2 (n), lb 1(7T), 5a 1(a), I b 2 , and 4a 1 canonical molecular orbitals are obtained using Hartree-Fock frozen-core functions and large basis sets of compact and diffuse normalizable Gaussians to describe the photoexcited and ejected electrons. The calculated discrete excitation spectra provide reliable zeroth-order approximations to both valence and Rydberg transitions, and, in particular, the 2b 2 (n)-msa 1 , npa 1 , npb 2 , and nda 2 IVO spectra are in excellent accord with recent experimental assignments and available intensity measurements. Convergent (S-T) photoionization cross sections in the static-exchange (IVO) approximation are obtained for the 15 individual partial channels associated with ionization of the five occupied molecular orbitals considered. Resonance features in many of the individual-channel photoionization cross sections are attributed to contributions frorn valencelike a 1 a*(CO), a 1 a*(CH), and b 2 a*(CH)/7Ty *(CO) molecular orbitals that appear in the photoionization continua, rather than in the corresponding one-electron discrete spectral intervals. The vertical electronic cross sections for 1 A 1 -+ 1 B 1 , 1 B 2 , and 1 A 1 excitations are in generally good accord with previously reported CI (s-T) predictions of continuum orbital assignments and intensities, although some discrepancies due to basis-set differences are present in the 1 B 1 and 1 B 2 components, and larger discrepancies apparently due to channel coupling are present in the 1 A 1 -+ 1 A 1 cross section. Partialchannel vertical electronic cross sections for the production of the five lowest parent-ion electronic states are found to be in general agreement with the results of very recent synchrotron-radiation photoelectron branching-ratio measurements in the 20 to 30 eV excitation energy interval. Most important in this connection is the tentative verification of the predicted orderings in intensities of the partial-channel cross sections, providing support for the presence of a strong ka 1