Vibrations in the B4 rhombic structure

Abstract

A double minimum six-dimensional potential energy surface (PES) is determined in symmetry coordinates for the most stable rhombic (D2h) B4 isomer in its 1Ag electronic ground state by fitting to energies calculated ab initio. The PES exhibits a barrier to the D4h square structure of 255 cm(-1). The vibrational levels (J=0) are calculated variationally using an approach which involves the Watson kinetic energy operator expressed in normal coordinates. The pattern of about 65 vibrational levels up to 1600 cm(-1) for all stable isotopomers is analyzed. Analogous to the inversion in ammonia-like molecules, the rhombus rearrangements lead to splittings of the vibrational levels. In B4 it is the B1g (D4h) mode which distorts the square molecule to its planar rhombic form. The anharmonic fundamental vibrational transitions of 11B4 are calculated to be (splittings in parentheses): G(0)=2352(22) cm(-1), nu1(A1g)=1136(24) cm(-1), nu2(B1g)=209(144) cm(-1), nu3(B2g)=1198(19) cm(-1), nu4(B2u)=271(24) cm(-1), and nu5(Eu)=1030(166) cm(-1) (D4h notation). Their variations in all stable isotopomers were investigated. Due to the presence of strong anharmonic resonances between the B1g in-plane distortion and the B2u out-of-plane bending modes, the higher overtones and combination levels are difficult to assign unequivocally.

Dissociation mechanisms of cluster ions resolved using ab-initio molecular orbital calculations

“…For example, the previous calculations proposed different atomic configurations from our results, e.g., linear B 0 4 , bipyramid B 0 5 and B þ 5 , or a rather three-dimensional frame, these exhibited imaginary frequencies or higher values of E T than our present results. For the structure B 0 4 , we found a rhombic structure, which is consistent with a recent report [10]. Table 1 compares the calculated value of the ionization potential (IP) for B 0 n clusters with measured data.…”

Electronic structure calculations on the C4 cluster

“…It has been found unstable ͓E R = 4.0 eV ͑CASSCF͒ and 3.03 eV ͑UCCSD͑T͔͒ lying over the lowest singlet and triplet states of r-C 4 . Recently, a similar situation was found for the B 4 cluster, 26 except that the D 4h transition state is lying only at 248.2 cm −1 favoring interconversion processes to occur via tunneling through this potential barrier. For C 4 , it is unlikely that such effect takes place for the low lying rovibrational levels of r-C 4 because of the large potential energy barrier separating both forms.…”

Density functional study of AlBn clusters for n=1–14

“…Boron is an electron-deficient semimetal and has a short covalent radius. Because of its high melting point and hardness it has been the subject of many studies [13][14][15][16][17][18][19][20]. Depending on the synthesis condition and the amount of boron, it has the ability to influence the structure and phase composition of materials [13,14].…”