Knowledge Bank

The Jahn-Teller effect on the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}E$ ground state of $VCl4$ has been investigated using ab initio restricted Hartree-Fock, Cl calculations, and spin-orbit Cl calculations with relativistic core potentials and gaussian double zeta plus polarization basis sets. The effects of the Jahn - Teller active E vibration were studied by computing the energy when opposite angles were simultaneously changed. The potential energy surface is described by $W=W(Td)+12kr2\pm (ar+12k\prime r2\cos (3\varphi ))$ where r and $\varphi$ are the vibrational coordinates in polar form, and k, a, and $k\prime$ are potential constants. At the SCF level, the minimum energy occurs with opposite angles opened by $3.5\circ$, and is $155.8cm-1$ below the tetrahedral energy. Closing these angles by $3.3\circ$ corresponds to a saddle point which is $4.5cm-1$ higher in energy. The force constant k and the first-order vibronic interaction constant a are calculated to be $0.124mdyn/\backslash AA$ and $2.75\times 10-5$ dyn respectively. At the CI level, the minimum energy occurs with opposite angles opened by $2.8\circ$, and is $97.4cm-1$ below the tetrahedral energy. Closing these angles by $2.6\circ$ corresponds to a saddle point on the surface which is $4.3cm-1$ higher in energy. the force constant k and the first-order vibronic interaction constant a are calculated to be $0.121mdyn/\backslash AA$ and $2.15\times 10-5$ dyn respectively. These values agree well with those found by electron $diffraction.1$ The quadratic vibronic interaction constant $k\prime$ is calculated to be $35.3cm-1/\backslash AA$ and has not been measured experimentally. Initial spin-orbit Cl calculations show that the spin-orbit interaction has little effect on the adiabatic potential energy surface.