ELECTRONIC-STRUCTURES AND STABILITIES OF GECN AND GE2CN IN HUCKEL THEORY

Some recent results about Ge(p)C(n)+ ions (p = 1,2; n < 6) produced in laser microprobe mass analyser experiments (LAMMA) show very marked alternations in the emission intensities I(Ge(p)C(n)+) as a function of the n and p parities. I(Ge(p)C(n)+) are maxima for even n. Thus, intensity maxima occur when the total atom number m of the aggregates is odd for GeC(n)+ (m = n + 1) and even for Ge2C(n)+ (m = n + 2). As a result, GeC(n)+ ions seem to behave as C(m)+ ions, whereas the behaviour of Ge2C(n)+ ions is quite similar to that of Ge(p)+ ions formed in SIMS or vaporization experiments on pure germanium. It is well known (correspondence rule) that the parity effect in the emissions corresponds to alternations in the ion stabilities. These results are analysed from a model built in Huckel approximation with hybridization. For p = 1, the clusters are assumed to be in sp hybridization as for C(m)+ ions, hence with linear shapes, and for p = 2, they would rather be in sp2 or sp3 hybridization as for Ge(p)+ ions. Relative stabilities and distributions of the energy levels of the aggregates are then calculated. The relative stabilities given for Ge(p)C(n)+ by this model show maxima for even n as in experiments, and we have thus a good agreement between our calculation results and the experimental data. Moreover, we found that Ge2C(n)+ would rather be in sp3 hybridization, that is under three dimensional shapes.