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A sophisticated spin-vibronic
model was developed to study electronic and nuclear dynamics in
two-fold degenerate electron systems (Windows Media, 174Kb). Eigenenergies and
eigenfunctions
of a model Hamiltonian are calculated in a basis set of products of
electronic, electron spin, and vibrational functions. The X2E ground
electronic state of the CH3O pyramidal (C3v)
system has been studied with the simultaneous treatment of the
spin-orbit coupling, the linear, quadratic, cubic, and quartic
Jahn-Teller interactions including multimode couplings,
and anharmonic effects up to the sixth order for the CH-stretching. The
group-theoretical analysis of the spin-vibronic Hamiltonian and its
eigenfunctions was performed in terms of irreducible representations (E3/2 and E1/2) of
the double C3v symmetry group. Vibronic and
anharmonic model parameters of CH3O were calculated with
numerical differentiation using ab initio energies of the CH3O
geometries distorted on normal coordinates. The equation-of-motion
coupled cluster method (EOMIP) with augmented core-valence basis sets
of triple-z
quality was applied in these calculations. The value of the spin-orbit
splitting in X2E CH3O
was calculated using multiconfiguration quasi-degenerate second order
perturbation theory with a complete active space CASSCF reference
wavefunction followed by a perturbative calculation of eigenvalues of
the full Breit-Pauli spin-orbit operator. The results of calculations
show the importance of inclusion of cubic vibronic terms into the model
Hamiltonian and the insignificance of quartic terms. The equation-of-motion coupled
cluster method (EOMIP) using a reference Slater determinant based on
the CH3S–-anion ground state with basis sets of
triple- and quadruple-z
quality was applied for numerical optimizations of geometries of
stationary points on adiabatic Jahn-Teller surfaces of the X2E ground state of CH3S
crossing at the C3v symmetry nuclear configuration.
Calculations by the multireference configuration interaction method and
multiconfiguration quasi-degenerate second order perturbation (PT2)
theory were also performed with use of a complete active space CASSCF
reference wavefunction. The linear and quadratic Jahn-Teller constants
were computed for each of three Jahn-Teller active modes. The potential
surfaces corresponding to spin-orbit states 2E3/2
and 2E1/2 were obtained
with eigenenergies of the full Breit-Pauli spin-orbit operator with a
PT2–CASSCF reference wavefunction. The one- and two-electron scalar
relativistic effects were included in CASSCF and spin-orbit
calculations. The calculated Jahn-Teller stabilization energy, the
barrier to pseudo-rotation, and the spin-orbit splitting are 93, 15,
and 358 cm–1 respectively. The Jahn-Teller
distortions are totally quenched by the strong spin-orbit coupling. |
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