A clue to the diffuse structure in ultraviolet spectra of the GeCl2 A-X transition.

Geometries, harmonic vibrational frequencies, and relative electronic energies of the two low-lying electronic states of the GeCl2 dimer have been calculated at the CIS(D) method with a cc-pVTZ basis set. Minima corresponding to three isomers on the ground-state potential energy surface have been characterized. The most stable dimer has a dissociation energy of 0.74 eV and has a trans-(GeCl2)2 structure. There is also a related, less stable, cis minimum. A third, Ci symmetry, isomer has a binding energy of 0.31 eV. It is found that this Ci isomer has substantial dipole transition strength to the first excited singlet state of the dimer with a vertical excitation energy of 3.33 eV. The transition energy (T0) between this Ci isomer and the van der Waals complex on the singlet excited state is predicted to be 4.007 eV, or a 1104 cm-1 blueshift with respect to that of the GeCl2 A-X transition. This finding may explain the diffuse structure which has been observed in the ultraviolet laser-induced fluorescence spectra of GeCl2. [ABSTRACT FROM AUTHOR]