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A new method of calculation of Franck-Condon factors which includes allowance for anharmonicity and the Duschinsky effect: Simulation of the HeI photoelectron spectrum of ClO2

By D. K. W. Mok, E. P. F. Lee, F. T. Chau, D. C. Wang and J. M. Dyke


A new method of Franck-Condon (FC) factor calculation for nonlinear polyatomics, which includes anharmonicity and Duschinsky rotation, is reported. Watson's Hamiltonian is employed in this method with multidimensional ab initio potential energy functions. The anharmonic vibrational wave functions are expressed as linear combinations of the products of harmonic oscillator functions. The Duschinsky effect, which arises from the rotation of the normal modes of the two electronic states involved in the electronic transition, is formulated in Cartesian coordinates, as was done previously in an earlier harmonic FC model. This new anharmonic FC method was applied to the simulation of the bands in the He I photoelectron (PE) spectrum of ClO2. For the first band, the harmonic FC model was shown to be inadequate but the anharmonic FC simulation gave a much-improved agreement with the observed spectrum. The experimentally derived geometry of the (X) over tilde (1)A(1) state of ClO2+ was obtained, for the first time, via the iterative FC analysis procedure {R(Cl-O)=1.414 +/- 0.002 Angstrom, angle O-Cl-O=121.8 +/- 0.1 degrees}. The heavily overlapped second PE band of ClO2, corresponding to ionization to five cationic states, was simulated using the anharmonic FC code. The main vibrational features observed in the experimental spectrum were adequately accounted for in the simulated spectrum. The spectral simulation reported here supports one of the two sets of published assignments for this band, which was based on multireference configuration interaction (MRCI) calculations. In addition, with the aid of the simulated envelopes, a set of adiabatic (and vertical) ionization energies to all five cationic states involved in this PE band, more reliable than previously reported, has been derived. This led also to a reanalysis of the photoabsorption spectrum of ClO2

Topics: Q, QD
Year: 2000
OAI identifier: oai:eprints.soton.ac.uk:18952
Provided by: e-Prints Soton

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  1. (2000). The first band of the ClO2 photoelectron spectrum: ~a! the experimental spectrum ~Ref. 4!, ~b! the simulated spectrum obtained using anharmonic FCFs, and ~c! the simulated spectrum using harmonic FCFs.
  2. (2000). The simulated photoelectron spectrum of the ClO2 1 3A2ÃClO2 X ˜ 2B1 ionization ~see the text for further details!.
  3. (2000). The synthesized second band of the ClO2 photoelectron spectrum ~lower trace! and the experimental spectrum ~upper trace! of Flesch
  4. (2000). case of the He I PE spectrum of ClO2, the combination of MRCI PEFs and the anharmonic FC code has been shown to work well.
  5. (2009). to Redistribution subject to AIP license or copyright; see http://jcp.aip.org/jcp/copyright.jspACKNOWLEDGMENTS The authors are grateful to the Research Grant Council ~RGC! of the Hong Kong Special Administrative Region ~Project Nos.
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