T. Karlsen et Kj. Borve, Accurate and approximate calculations of Franck-Condon intensities in the carbon 1s photoelectron spectrum of methane, J CHEM PHYS, 112(18), 2000, pp. 7979-7985
The level of theory needed in order to accurately compute the bond contract
ion following core ionization in methane is examined with an emphasis on on
e-electron bases and treatment of electron correlation. At our highest leve
l of theory, including core-valence electron correlation, a value of 4.82 p
m is computed for the bond contraction in core-ionized methane, in good agr
eement with experimental findings. The associated potential energy curve in
the symmetric stretching coordinate is used to form relative intensities o
f the peaks in the C 1s photoelectron spectrum of methane. For use in more
approximate studies, it is proposed that the ionized core may be convenient
ly represented by effective core potentials during geometry optimization, a
nd the prospect of this approach is explored in some depth. (C) 2000 Americ
an Institute of Physics. [S0021- 9606(00)00618-8].