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Theoretical studies of photoexcitation and ionization in H_2O

Diercksen, G. H. F. and Kraemer, W. P. and Rescigno, T. N. and Bender, C. F. and McKoy, B. V. and Langhoff, S. R. and Langhoff, P. W. (1982) Theoretical studies of photoexcitation and ionization in H_2O. Journal of Chemical Physics, 76 (2). pp. 1043-1057. ISSN 0021-9606. doi:10.1063/1.443072.

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Theoretical studies are reported of the complete dipole excitation and ionization spectrum in H_2O 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 synchrotron‐radiation studies of partial‐channel photoionization cross sections. The various calculated excitation series in the outer‐valence (1b(^−1)_1, 3a(^−1)_1, 1b(^−1)_2) region are found to include contributions from valence‐like 2b_2 (σ*) and 4a_1(γ*) virtual orbitals, as well as appropriate nsa_1, npa_1, nda_1, npb_1, npb_2, ndb_1, ndb_2, and nda_2 Rydberg states. Transition energies and intensities in the ∼7 to 19 eV interval obtained from the present studies are seen to be in excellent agreement with the measured photoabsorption cross section, and to provide a basis for detailed spectral assignments. The calculated (1b(^−1)_1)X(^ 2)B_1, (3a_1(^−1))^2A_1, and (1b_2(^−1))(^2)B_2 partial‐channel cross sections are found to be largely atomic‐like and dominated by 2p→kd components, although the 2b_2(σ*) orbital gives rise to resonance‐like contributions just above threshold in the 3a_1→kb_2 and 1b_2→kb_2 channels. It is suggested that the latter transition couples with the underlying 1b_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 inner‐valence (2a_1(^−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 1a_1 oxygen K‐edge electron energy‐loss profile in H_2O are seen to be clarified fully by the present calculations.

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Additional Information:© 1982 American Institute of Physics. Received 3 August 1981; accepted 28 August 1981. It is a pleasure to acknowledge the support of the National Science Foundation, and of the Donors of the Petroleum Research Fund, administered by the American Chemical Society. The kind hospitality provided to P. W. L. by Professor Noel Hush at the University of Sydney is also gratefully acknowledged. We thank W. von Niessen for providing calculated inner-valence-shell ionization energies and spectroscopic factors in H20, and the authors of Ref. 3 for making the results of their synchrotron-radiation studies available prior to publication.
Funding AgencyGrant Number
American Chemical Society Petroleum Research FundUNSPECIFIED
Subject Keywords:water; excitation; photoionization; ground states; eigenfunctions; equilibruim; geometry; oscillator strengths; energy−level transitions; energy; brightness; correlations; experimental data; dipoles; cross sections; energy absorption
Issue or Number:2
Classification Code:PACS: 33.80.Eh; 31.15.-p; 33.20.-t
Record Number:CaltechAUTHORS:20120716-144432495
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Official Citation:Theoretical studies of photoexcitation and ionization in H[sub 2]O G. H. F. Diercksen, W. P. Kraemer, T. N. Rescigno, C. F. Bender, B. V. McKoy, S. R. Langhoff, and P. W. Langhoff, J. Chem. Phys. 76, 1043 (1982), DOI:10.1063/1.443072
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32485
Deposited On:16 Jul 2012 22:03
Last Modified:09 Nov 2021 21:27

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