UK Physics & Astronomy Physics & Astronomy
Colloquium


Colloquium



3:30 PM, Friday, February 1, 2002


Room 155, Chem-Phys Building







Dr. Robert N. Compton


Departments of Chemistry and Physics
The University of Tennessee





Multipole-Bound Molecular Anions





Recent experiments in the field of negative ion physics have shown that in some cases it is useful to describe the binding of an electron to a molecule as a result of the dominant multipole moment of that molecule (e.g., dipole, quadrupole, etc.) together with the polarizability attraction. These anions are exceedingly weakly bound and are subject to collisional detachment as well as detachment by modest electric fields. Some general theoretical statements can be made as to the "minimum" dipole moment required to bind an electron to a molecule but similar statements for the molecular quadrupole are not as well described. In cases where a molecule has a dipole or quadrupole moment of sufficient strength to permanently bind an extra electron but also possesses a bound valence anion, the multipole-bound state and valence state interact to form a coupled system. In this sense the dipole (or quadrupole) states can act as entrance channels or "doorway" states to the formation of the more strongly bound valence anion states. The concept of electron molecule multipole expansion is especially useful in describing multiply-charged negative ions. The combined monopole (Coulomb repulsion) and polarizability attraction of an electron with a molecular negative ion gives rise to a Coulomb barrier for the addition or removal of the extra electron. The Coulomb barrier can act to make a multiply charged anion more stable with respect to electron loss than its singly charged parent. This simple picture qualitatively explains many of the prominent features of multiply charged anions.



*** Refreshments served at 3:15 PM ***


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Send comments to
Moshe Elitzur
moshe@pa.uky.edu



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On 3 Jan 2002, 14:04.