"Infrared photodetachment of Ce-: Threshold spectroscopy and resonance structure" Walter, C. W.; Gibson, N. D.; Janczak, C. M.; Starr, K. A.; Snedden, A. P.; Field, R. L. Physical Review A 76, 052702 (2007).
The authors set out to use the results of photodetachment spectroscopy to analyze the transition from Ce-1 to Ce. After searching online, we found that this method involves a photon-stimulated detachment of an electron using a laser beam of specific energy. So their use of “tunable laser photodetachment” indicates that they’re looking at the specific effect of photon energy on this transition.
In analyzing the results, the authors used a variety of theoretical calculation methods and prior experimental results to propose a mechanism of the observed results. They attempted to identify the transition from ground state Ce- to ground state Ce in order to derive the electron affinity of Ce.
The results were complicated by the variety of transitions possible, most of which involve excited states of Ce-. For example, the authors suggest that, rather than absorbing a photon and immediately ejecting an electron, Ce- can move to an excited state by absorbing one photon, and that absorption of an additional photon might provide sufficient energy to allow the electron to detach. The authors determine an electron affinity value of 0.65 eV which was in great agreement with previous results. The authors suggest in their conclusion that further investigation is needed to derive the distinction between these two processes.
We were unsure of exactly what the authors meant by ‘resonance’ in the article. It seemed that what they termed resonance was an excitation. Additionally, we were not sure how they were defining and analyzing ‘unbound states’ in the paragraph on page 7 that starts with, “Peaks in photodetachment spectra generally arise from…” Understanding what these unbound states are would help to clarify what they define as resonance.
We found it interesting and probably worth discussing, that curves were fitted to experimental data and used to elucidate the data in Table I, rather than the other way around.
Posted by Julia Malik and Randy Ruffner
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The author's mentioned in their introduction that Ce-1 has been the most studied negative ion lanthanide, but I was just curious into what other lanthanide's, if any, have been examined using the same experimental parameters, by any of the authors cited. And also how values have compared with these other ions. Are there trends within the data about the electrons and transitions of interest among the different lanthanides? The experimental procedure must be adequate since their observed results match very closely to other results obtained by other research groups. Perhaps other lanthanide's haven't been examined yet because the method is new and author's were looking to verify it or that cerium is the easiest lanthanide to work with?
ReplyDeleteI have a comment about the use of the Wigner Threshold law. They mention on page 5 in the second column halfway down that they vary an adjustable parameter, a, the amplitude constant to find the best visual match to the continuum component. This may be trivial, but I’m wondering if this has any similarities to the Hartree-Fock sort of approximations we did for multi-electron atoms. I realize the study isn’t investigating a wavefunction, but it seems similar in that they varied one component and then repeated with different energy values until they found the range that was consistent with the data.
ReplyDeleteAnother thing I was curious about was about the electron configurations. What do the “Go4”, “Ho7/2”, etc., mean in ([Xe]4f5d6s2Go4)? Is this relevant to the atoms excitation or state?
I have a comment about the use of the Wigner Threshold law. They mention on page 5 in the second column halfway down that they vary an adjustable parameter, a, the amplitude constant to find the best visual match to the continuum component. This may be trivial, but I’m wondering if this has any similarities to the Hartree-Fock sort of approximations we did for multi-electron atoms. I realize the study isn’t investigating a wavefunction, but it seems similar in that they varied one component and then repeated with different energy values until they found the range that was consistent with the data. Another thing I was curious about was about the electron configurations. What do the “Go4”, “Ho7/2”, etc., mean in ([Xe]4f5d6s2Go4)? Is this relevant to the atoms excitation or state?
ReplyDeleteIn relation to what Ashley said, the article mentions that bound - bound E1 transitions in the negative ion make Ce- a good candidate for a future study as only the second example of a negative ion with bound states of opposite parity. I was wondering what the first example was for the article seems to neglect this to mention this fact. I was also confused about their electron configurations just as Ashley and Brooke are.
ReplyDelete