ANALYSIS AND ASSIGNMENT OF THE OPTICAL-ABSORPTION TRANSITIONS IN CUCL2 WITH GAUSSIAN DENSITY-FUNCTIONAL CALCULATIONS

Some vibrational and electronic properties of the CuCl2 molecule are a nalyzed in order to characterize the electronic states and assign the bands seen on the optical absorption spectra. Equilibrium distances, t otal energies, electronic structure and harmonic vibrational frequenci es of the low-lying states are calculated with the functional density method, in the unrestricted spin formalism, at two levels of theory fo r the exchange and correlation potential, the local and so-called non- local spin density approximations. All the results are compared with r ecent experimental data. The ground state is confirmed to be 1PI(g), w ith a linear coordination as for the excited d --> d states (2SIGMA(g) +, 2DELTA(g)) and charge-transfer states (2PI(u), 2SIGMA(u)+ ). These low-lying states are in the following sequence: 2SIGMA(g)+, 2PI(u), 2D ELTA(g), 2SIGMA(u)+, in order of increasing energies, different from t hose of previous Hartree-Fock results. Their harmonic vibrational freq uencies are given and the oscillator strengths of the absorption trans ition from the ground state to these states are calculated. Therefore we propose a new assignment for the optical near infrared transitions (absorption and emission) to SIGMA(g)+ <-> 2PI(g) which would explain the lack of spin-orbit components of the emitting level in the experim ental spectra, while the red ones could be 2PI(u) <-> 2PI(g), as alrea dy proposed in earlier works.