From owner-chemistry@ccl.net Wed Nov 30 01:28:01 2005 From: "Alan Shusterman alan{:}reed.edu" To: CCL Subject: CCL: question on molecular orbitals in CO and NO Message-Id: <-30116-051130010136-4510-soKY9vKel0mcYy0+6Wh7Hw a server.ccl.net> X-Original-From: Alan Shusterman Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=windows-1252; format=flowed Date: Tue, 29 Nov 2005 22:01:05 -0800 MIME-Version: 1.0 Sent to CCL by: Alan Shusterman [alan]-[reed.edu] Sengen, It's an interesting quote, and it's too bad that we don't have more context for it because it can be interpreted in several ways. Probably you should write Professor Hoffmann and ask *him* what he means. His answer would provide "experimental proof". Now for my 2 cent interpretation... First, I think the quote does not imply orbitals are experimental observables. Second, a Hoffmann paper that comes to mind (and I hope my memory is not playing tricks on me) is an analysis of through-bond effects on the PE spectra of 1,2-diamines. If I recall correctly, different PE spectra were predicted for N lone pairs that a) do not interact, b) interact through-space, and c) interact through-bond, and Hoffmann's Extended Huckel MO calculations indicated the last option was most likely. I think the PE data supported his model. So based on this string of questionable memories, my expanded reading of Hoffmann's quote would go like this: I have calculated orbital interactions for molecules, and I have used these orbitals to predict experimental properties that others tested (and ultimately confirmed) using PE spectroscopy. Third, the on-line article you point to is a celebration of Albert Einstein, especially the photoelectric effect. I think Hoffmann was just trying to say that PES has been useful for his research because it has told him whether his (highly parameterized) models were on a realistic track or not. As such, it shows one more way that orbital models make contact with experiment, but it is very far from a claim of experimentally observed orbitals. -Alan Sengen Sun sengensun(~)yahoo.com wrote: >Sent to CCL by: Sengen Sun [sengensun/a\yahoo.com] >My apologies if I am a bad guy again. > >But in contrast to the recent discussions by Wayne >Steinmetz and Ulrike Salzner, Roald Hoffmann recently >said: “Photoelectron spectroscopy has provided me with >experimental proof of the ways orbitals interact.” >(See: >http://acswebcontent.acs.org/chemistry/autumn_2005.pdf) > > > > -- Alan Shusterman Chemistry Department Reed College Portland, OR 97202-8199 503-517-7699 http://academic.reed.edu/chemistry/alan/ "Yield and overcome; Bend and be straight." Lao Tzu 22