Theoretical Study On Weakinteraction In Rare Gas Mixed Cluster

The syntheses of rare gas contained clusters bring forward a considerable challenge toward the classical chemical bond theory and thus the investigation on it has very important significance. The present work studies the molecular bonding furtherly and can develop the interaction theory greatly. The anslysis of the structures, physical and chemical character, the electron correlation and relativistic effects can shed light on the principle of the bonding; moreover, can develop the technique in the investigation on the weak interaction clusters.The electronic states, dissociation energies and potential energies of RgX― (Rg=Kr, Xe; X=Br, I) were investigated at CCSD(T) theoretical level. The potential energies were fit to a four parameters Murrell-Sorbie function by least-squares procedure. The force constants and spectral constants were derived by the fitted Murrell-Sorbie parameters. These correlation-bound complexes RgX(Rg=Kr, Xe, X=Br, I) are not bound at self-consistent field(SCF) level and only weakly bound at the correlated levels. It clearly shows the importance of the electron correlation effects for the present van der Waals complexes. In the present study, we have systematically investigated the heavier RgX(Rg=Kr, Xe, X=Br, I) to have a further insight into the correlation energy of the RgX vdW complex. A new method to derive the dispersion coefficient C6 by fitting the intermonomer electron correlation energies to C6R-6 function is introduced. The present C₆ values are compared with the corresponding theoretical ones.The optimized geometries and vibrational frequencies of Rg₂X^-(Rg=Ar, Kr, Xe; X=Br, I) and its neutral were calculated at HF, MP2, and CCSD(T) theoretical levels. At CCSD(T) theoretical level, the anion systems Rg₂X^- have ¹A₁ electronic state and C_2v bent structure with small bond anglesθ(Rg-X-Rg) about 55.0°⁶2.0°, which is in line with experimentally known small angles. The neutral systems Rg₂X have ²A₁ electronic state and C2v bent structure as its anion. The dissociation energies of the anions exceed those of the neutrals, because in the former ion/induced dipole forces are present while in the neutrals only induced polarizability comes into play. The electron correlation effects and relativistic effects are investigated at CCSD(T) theoretical level. Both effects have strong influence on the geometries and stabilities of the present species; they shorten the bond length, reduce the bond angle, increase the vibrational frequencies and thus enhance the stability. The calculated electron affinities are in good agreement with the experimental values available. High quality gh-functions play a critical role in describing polarizability of the present systems, the gh-function corrections to dissociation energy were investigated at MP2 level to be about 30%, and the best De at CCSD(T) theoretical level were estimated. The orderings of EA and De indicate that the Xe₂X^- is the most stable species of the present systems due to its greater polarizability.The MP2 calculations reported in this study find the most stable structures of the Xe_nI^- (n=2-6) to be C_2v, C_3v (tetrahedron), C_2v (butterfly), C4v (octahedron) and C_5v (decahedron), respectively. The calculated results indicate that Xe-I^-"bond"is about four times stronger than the Xe-Xe"bond", thus in the global minimum energy structure of XenI^-(n=2-6), all the Xe atoms contact the central I anion, allowing the maximum Xe-I^-"bond"to be formed. Next, the Xe atoms are grouped in a way that the number of Xe-Xe"bonds"is maximized. Theoretical results indicate that the dissociation energies of the present clusters increase monotonically as the size of n increase, which is different from the fragmentation energies. The I^- was found to be located inside the Xe cluster, thus the Xe-I^-"bonds"increase monotonically as the size of n increase while the Xe-Xe"bond"do not have the same behavior, it results in irregular variable trend of the fragmentation energies. By the chosen criterion, Xe₆I^<sub> has the biggest fragmentation energies and thus it is the most stable specie. The calculated electron affinities increase monotonically as the size of n increase and compare very well with the experimental values.