DP Seminar

[Luca Ferialdi]

Department of Physics - University of Trieste

Wednesday 16 March 2011 - 3.00 pm
Room 204 (2nd floor LB)

dr. Mohammad Bahrami
(University of Trieste)

Title: Hund Paradox: on the stability of molecular structures

Abstract:
The “Hund paradox” or “chirality problem” concerns the conflicting
relation between a variety of stable molecular properties and the
stability of their corresponding nuclear configuration wavefunctions, in
particular for chiral molecules. A large number of molecular properties
(e.g., molecular geometries and dipole moments which depend on the nuclear
configuration) are stable properties of the chiral molecules in many
different physical conditions (e.g., temperature, pressure, and the size
of molecule). However, not their corresponding nuclear wavefunctions
(i.e., chiral states) but their superpositions are the eigenstates of the
molecular Hamiltonian. This means the configuration-dependent molecular
properties should not be observed as the stable molecular properties of
chiral molecules unless some physical mechanisms stabilize the
corresponding chiral states and destroy the superposition. Hund partially
resolved the problem with regard to the phenomenon of the quantum
tunneling. Several other attempts have been made to explain the Hund
paradox by either taking into the account a small parity-violating term in
molecular Hamiltonian, or by adding non-linear and stochastic terms to the
dynamics because of interactions with a surrounding environment. The
non-linear terms are related either due to the coupling of system with
photons or with phonons, or due to the environmental effects such as
intermolecular interactions and collisions. Resolving the problem by
non-linear dynamics has recently found lots of attentions since in some
particular occasions it seems to provide the experimental conditions under
which the transition from tunneling mechanism into the chiral
stabilization happens, i.e., the transition from quantum to classical. In
this talk, we will investigate different approaches to resolve the Hund
paradox, in particular the role of molecular parity-violating energies. We
will compare the results of different formulations, and discuss the open
questions and the possible resolutions.