October 31, 2005 - Halloween Colloquium
Behind the cut to prevent whining. :p
October 31
Dr. Robert Compton, UT Departments of Chemistry and Physics
Multiple-Bound Molecular Anions
Recent experimental and theoretical studies 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 or low-energy photons. A plot of the electron affinities for over fifty dipole-bound anions shows a minimum dipole moment of ~ 2.5 Debye to bind an excess electron. This agrees with general theoretical estimates of the “minimum” dipole moment required to bind an electron to a polar molecule. Recently, we have shown that the succinonitrile molecule can support both a dipole-bound anion in its gauche form (EA ~ 108 meV) and a quadrupole-bound anion in its trans form (EA ~ 20 meV)[PRL, 92, 83003].
The concept of electron-molecule multipole expansion is especially useful in the description of 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. This simple picture qualitatively explains many of the prominent features of multiply-charged anions. The majority of this talk will discuss recent studies on the formation mechanisms and subsequent collision induced dissociation of multiply-charged anions.
Dr. Compton (Cool dude. Had him for PHY506. Went to a talk he gave at Berea on Chirality.) talked about Anions bound by either dipoles or quadropoles. It was a pretty interesting talk, though that's more or less because of the way his talks go rather than the subject. He showed experimental data, had neat pictures, and talked about what's going on.
He also demonstrated his model by using electrically charged balloons to simulate the dipole and electron. This involved, of course, rubbing the balloon on his head, then complaining about not having enough hair to make the experiment work when it took a bit of fiddling to get it to do what he wanted.
I also got to hear about the people in his research group having kids. Some guy who was an author on a paper he wrote working at some school while the guy's wife got her degree there. I also got updated on the current financial status of one John Fenn (Noble Prize winner that graduated from Berea like me and Dr. Compton).
I mean, it's not really what Bob's talking about that is the subject of his talks, it's really all the other things he brings up. And that's what makes them interesting. As for the actual subject, the abstract above hits the relevant points.
Oh, they also changed colloquium forms on me, so I need to rebuild my stockpile.
And I helped Sam (from Berea, not Ninjaweazel) out with figuring out what he did on his test for Dr. Breinig's PHY513 class on this one problem.
October 31
Dr. Robert Compton, UT Departments of Chemistry and Physics
Multiple-Bound Molecular Anions
Recent experimental and theoretical studies 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 or low-energy photons. A plot of the electron affinities for over fifty dipole-bound anions shows a minimum dipole moment of ~ 2.5 Debye to bind an excess electron. This agrees with general theoretical estimates of the “minimum” dipole moment required to bind an electron to a polar molecule. Recently, we have shown that the succinonitrile molecule can support both a dipole-bound anion in its gauche form (EA ~ 108 meV) and a quadrupole-bound anion in its trans form (EA ~ 20 meV)[PRL, 92, 83003].
The concept of electron-molecule multipole expansion is especially useful in the description of 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. This simple picture qualitatively explains many of the prominent features of multiply-charged anions. The majority of this talk will discuss recent studies on the formation mechanisms and subsequent collision induced dissociation of multiply-charged anions.
Dr. Compton (Cool dude. Had him for PHY506. Went to a talk he gave at Berea on Chirality.) talked about Anions bound by either dipoles or quadropoles. It was a pretty interesting talk, though that's more or less because of the way his talks go rather than the subject. He showed experimental data, had neat pictures, and talked about what's going on.
He also demonstrated his model by using electrically charged balloons to simulate the dipole and electron. This involved, of course, rubbing the balloon on his head, then complaining about not having enough hair to make the experiment work when it took a bit of fiddling to get it to do what he wanted.
I also got to hear about the people in his research group having kids. Some guy who was an author on a paper he wrote working at some school while the guy's wife got her degree there. I also got updated on the current financial status of one John Fenn (Noble Prize winner that graduated from Berea like me and Dr. Compton).
I mean, it's not really what Bob's talking about that is the subject of his talks, it's really all the other things he brings up. And that's what makes them interesting. As for the actual subject, the abstract above hits the relevant points.
Oh, they also changed colloquium forms on me, so I need to rebuild my stockpile.
And I helped Sam (from Berea, not Ninjaweazel) out with figuring out what he did on his test for Dr. Breinig's PHY513 class on this one problem.