OPTICAL-SPECTRA OF MATRIX-ISOLATED PALLADIUM ATOMS .3. MATRIX EFFECTSON THE ELECTRONIC-STRUCTURE OF PD ATOMS

The detailed analysis of the optical spectra (uv-visible absorption an d emission and laser-induced luminescence) of palladium atoms isolated in solid argon, kripton and xenon matrices at 12 K reveal that in the se environments the Pd atoms are isolated in three main trapping sites . In the two interstitial sites (tetrahedral and octahedral) of a cubi c closed-packed (CCP) crystal structure of the inert solid, the Pd ato ms preserve the gas-phase electronic ground state configuration 4d(10) S-1(0), but in each one the deactivation of electronic excited states is quite different. In a substitutional site the atom changes the gas -phase electronic ground state configuration 4d(10) to one of 4d(9)5s( 1) electronic configuration, that is the D-3(3) State becomes the grou nd state. The broad band luminescence studies reveal that in the Pd/Ar and Pd/Kr systems there exists a very efficient process of population of the very long-lived 4d(9)5s(1) D-3(3) metastable state from Pd(4d( 10) S-1(0)) atoms isolated in a interstitial octahedral site. This pro cess also occurs in the Pd/Xe system, but seems less efficient. The oc currence of this process brings as consequence that the optical spectr a show more bands than expected. On the other hand, it was found that the pass from Ar to Xe matrices has a deep effect on the allowness of forbidden transitions, this is clearly manifested in the absorption an d emission spectra of Pd(4d(10) S-1(0)) atoms isolated in an interstit ial tetrahedral site of a Xe matrix where unambiguously the bands of t hese spectra can be assigned. This effect seems absent in the Pd/Ar sy stem, but in Pd/Kr it is only manifested in the more sensible excitati on and emission spectra. As consequence of (i) the coexistence of Pd a toms in two electronic ground states, (ii) the fast population of a lo ng-lived metastable state and (iii) the heavy atom effect: the uv-visi ble absorption spectra of Pd atoms isolated in Ar, Iir and Xe matrices will be a superposition of uv-visible absorption spectra whose contri butions from (i) to (iii) will depend of the matrix (Ar, Kr and Se). T his brings as consequence that the net uv-visible absorption spectra o f Pd atoms isolated in Ar and Kr matrices looks similar, but is substa ntially different in a Xe matrix.