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Photoexcitation and ionization in molecular fluorine: Stieltjes–Tchebycheff calculations in the static-exchange approximation

Orel, A. E. and Rescigno, T. N. and McKoy, B. V. and Langhoff, P. W. (1980) Photoexcitation and ionization in molecular fluorine: Stieltjes–Tchebycheff calculations in the static-exchange approximation. Journal of Chemical Physics, 72 (2). pp. 1265-1275. ISSN 0021-9606. doi:10.1063/1.439187.

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Theoretical investigation of outer (1pig, 1piu, 3sigmag) and inner (2sigmau, 2sigmag) valence-shell electronic photoexcitation and ionization cross sections in molecular fluorine are reported employing separated-channel static-exchange calculations and Stieltjes–Tchebycheff (S–T) moment-theory techniques. The discrete vertical electronic 1pig excitation series are found to be in good agreement with recent spectral assignments and previously reported theoretical studies, and those for 1piu, 3sigmag, 2sigmau and 2sigmag excitations are in general accord with position and intensity estimates based on quantum-defect analysis. Certain of the partial-channel photoionization cross sections in F2 are seen to exhibit resonancelike features similar to those reported recently in related S–T studies of photoionization in N2, CO, and O2. The resonances can be attributed to valencelike and pre-Rydberg diabatic states that cross the outer limbs of appropriate Rydberg series and corresponding ionic-state potential curves as functions of internuclear coordinate, giving rise to large continuum transition intensities at the ground-state equilibrium internuclear separation. In contrast to the situation in N2, CO, and O2, however, there is no evidence of a resonance like sigma-->sigma* feature in the 3sigmag-->ksigmau photoionization channel in F2. Rather, this resonance in F2 appears as a strong N-->Vg transition below the 3sigmag ionization threshold, and the corresponding partial-channel photoionization cross section is seen to be structureless. Although experimental studies of partial-channel photoionization cross sections are apparently unavailable for comparison, the calculations reported here should provide reliable approximations to the dipole excitation/ionization spectra in F2, and are helpful in understanding and clarifying the dependences of photoionization spectra in light diatomic molecules on shell occupancy and equilibrium internuclear separation when compared with the results of previous studies of photoionization in N2, CO, and O2.

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Additional Information:Copyright © 1980 American Institute of Physics. Received 4 June 1979; accepted 24 September 1979. Acknowledgment is made to the National Science Foundation for support provided to B.V.M., and to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, and to the National Research Council, for providing support to P.W.L. The kind hospitality of J.O. Arnold and S.R. Langhoff of the NASA-Ames Research Center Computational Chemistry Group, and of D. Bershader of the Department of Aeronautics and Astronautics, Stanford University, to P.W.L. is also gratefully acknowledged. The work of T.N.R. and A.E.O. was performed under the auspices of the U. S. Energy Research and Development Administration under Contract No. W-7405-Eng-48.
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National Science FoundationUNSPECIFIED
Petroleum Research FundUNSPECIFIED
National Research CouncilUNSPECIFIED
Energy Research and Development AdministrationW-7405-Eng-48
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Deposited On:22 Oct 2008 00:11
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