Search results for "Energy minimum"
showing 3 items of 3 documents
Prolate yrast cascade in183Tl
2000
The yrast sequence in ${}^{183}\mathrm{Tl}$ has been studied for the first time in recoil-mass selected \ensuremath{\gamma}-ray spectroscopic measurements. A rotational-like cascade of seven transitions is established down to the band head with probable spin and parity ${(13/2}^{+}).$ Unlike in the adjacent odd-mass Tl nuclei, prompt \ensuremath{\gamma} decay from the yrast band to a lower lying weakly deformed (oblate) structure is not observed. These features are consistent with the predicted drop of the prolate band head in ${}^{183}\mathrm{Tl}$ compared to ${}^{185}\mathrm{Tl}.$ The implications for the prolate energy minimum in odd-mass Tl nuclei at the neutron ${i}_{13/2}$ midshell $(…
A theoretical study of solvent effects on the conformational equilibria of neutral glycine in aqueous solution
2003
Abstract In this work conformational equilibrium of neutral glycine in solution is systematically investigated by using DFT and MP2 methods combined with solvent continuum models. A systematic exploration of the potential energy surface and full geometry optimizations for several conformers have been carried out in the gas phase and aqueous solution at the MP2/6-31+G** and B3LYP/6-31+G** levels. Zero-point and thermal contributions to the free energy have been obtained at the B3LYP level. Both theoretical levels lead to very similar results, in geometrical and energetic terms, both in the gas phase and in solution. Solvent effects play an important role on the conformational equilibria of n…
Informational rigidity in mesitylene-based calix[4]arenes adopting a 1,3-alternate conformation
2000
Abstract Two chiral derivatives of a mesitylene-based calix[4]arene known to exist in the 1,3-alternate conformation were prepared by the attachment of homochiral residues to the four exo -hydroxy groups. Thus, the enantiotopic protons of the central scaffold became diastereotopic, leading to a doubling of their 1 H NMR signals in one example. From the temperature independence of the NMR spectrum, a lower limit of 24.2 kcal/mol could be estimated for the barrier of ring inversion. MM3 calculations confirm the 1,3-alternate conformation as the energy minimum, and estimate a barrier of 25.7 kcal/mol for the 1,3-alternate-to-1,3-alternate* interconversion process. This high barrier is due to t…