No abstract

In brane world models our universe is considered as a brane imbedded into a higher dimensional space. We discuss the behaviour of geodesics in the Randall-Sundrum background and point out that free massive particles cannot move along the brane only. The brane is repulsive, and matter will be expelled from the brane into the extra dimension. This is rather undesirable, and hence we study an alternative model with a non-compact extra dimension, but with an attractive brane embedded into the higher dimensional space. We study the linearized gravity equations and show that Newton's gravitational law is valid on the brane also in the alternative background. *

Ab initio molecular orbital calculations on trimethyl phosphate (TMP) were done using 6-31G* and 6-31G** basis sets, both at RHF and MP2 levels of theory. We located three minima corresponding to C 3 , C 1 , and C s symmetries, given in order of increasing energies. At the MP2/6-31G** level, the energy difference between the C 3 and C 1 conformers was 0.56 kcal/mol, while that between the C 3 and C s was 1.43 kcal/mol. Our observations are at variance with an earlier ab initio calculation, employing smaller basis sets, STO-3G* and 4-31G*, which had reported that the C 1 conformer was the lowest in energy. Furthermore, the earlier calculation did not report the occurrence of a minimum corresponding to the C s symmetry. Vibrational frequency calculations were done at the HF and MP2 levels. The computed frequencies were found to compare well with experimental vapor phase and matrix isolation data reported earlier, leading to a definitive assignment of the infrared features of TMP.

No abstract

No abstract

No abstract

Hydrogen-bonded H‚‚‚π complexes of C 2 H 2 and C 2 H 4 were studied both computationally and experimentally. Computationally, C 2 H 2-C 2 H 4 clusters ranging from 1:1 to 6:1 stoichiometries were identified. Using matrix isolation infrared spectroscopy, the 1:1 adduct was studied in an argon matrix. Formation of these adducts was evidenced by shifts in the vibrational frequencies of the acetylene and ethylene submolecules in the complex. The molecular structure, vibrational frequencies, and stabilization energies of the complexes were calculated at the HF, MP2, MP2(full), and B3LYP levels of theory by employing basis sets ranging from 6-31G(d,p) to 6-311++G(2d,2p). Both computations and experiments showed that two types of complexes are formed, one in which acetylene acts as a proton donor to the π cloud of ethylene and another in which ethylene acts as the proton donor to the π cloud of acetylene. Structures, interaction energies, and vibrational frequencies have also been obtained for 1:2, 1:4, and 1:6 complexes of ethylene and acetylene. This work presents a case study of hydrogen-bonded clusters formed through the H-π interaction.

No abstract