Electronic structure and potential energy surfaces of positive ions of group IV tetramers (Ge4+-Pb4+)

Abstract

The interest in group IV clusters in particular is attributed in part to their technological importance since group IV materials (Si, Ge) are used in the fabrication of microelectronic devices. Smalley and co-workers have studied the photofragmentation patterns of Si; and Gent cluster ions, as well as Si; and Ge; ions!*'* They found certain interesting trends in the photofragmentation patterns of these species. Martin and Schaber have obtained the mass spectra of both tin and germanium clusters.26 They too found several fascinating trends in the mass spectra of these species. In particular, they found that the mass spectra of tin clusters exhibit a gradual decrease in the intensity for up to 13-atom clusters. In dramatic contrast, the leatom cluster was absent in the mass spectrum while the intensities of the peaks which correspond to 15- and 16-atom clusters increase again. Magic numbers were also found for the 6- and 10-atom clusters of Si,+ and Gent. Lineberger and co-~orkers~~ have recently obtained the photodetachment spectra of Si, and Pb; clusters. They have analyzed the spectra of dimers in considerable detail and found very good agreement with the results of previous theoretical calculations on Pbz and Snz (see ref 1 for a review of computed results on dimers and trimers). Experimental studies have also been made on positively charged Pb clusters.34 There are laser-inducedfluorescence studies on dimers of Pb and Sn. Neumark and ~o-workers~~ have obtained negative photodetachment spectra of Si4-. Thm are several recent experimental and theoretical Among the heavier group IV clusters, Si4 has been the most studied molecule theoretically.19P Pacchioni and K0ute42l@~ have studied the ground-state properties of Ge4. There are theoretical studies on Sn3, Si4, Gq, and Ge4. Raghavachari and co-worker~~~,~~ have studied Si, (n - 3-10), excited states of Si3 and Si4, among other related species. These studies have yielded a wealth of information on silicon clusters. While considerable information has been accumulated on silicon clusters, this is not the case for heavier group IV clusters.