From chemistry-request _-at-_)ccl.net Thu Jan 20 11:03:37 2005 Received: from electra.cc.umanitoba.ca (electra.cc.umanitoba.ca [130.179.16.23]) by server.ccl.net (8.12.8/8.12.8) with ESMTP id j0KG3ai3023619 for ; Thu, 20 Jan 2005 11:03:36 -0500 Received: from Fledermaus (net05.chem.umanitoba.ca [130.179.48.85]) (authenticated bits=0) by electra.cc.umanitoba.ca (8.13.0/8.13.0) with ESMTP id j0KEwi75001005 for ; Thu, 20 Jan 2005 08:58:44 -0600 (CST) Message-Id: <200501201458.j0KEwi75001005..at..electra.cc.umanitoba.ca> Reply-To: From: "Phil Hultin" To: "Computational Chemistry List" Subject: RE: orbitals and reality Date: Thu, 20 Jan 2005 08:58:39 -0600 Organization: Dept. of Chemistry, U. of Manitoba MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook, Build 11.0.6353 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 In-Reply-To: <20050117224622.17167.qmail..at..web51304.mail.yahoo.com> Thread-Index: AcT88ILMibIaDKhnSt2LKiOpr0iqVwADrJow X-Spam-Status: No, hits=0.0 required=7.5 tests=none autolearn=no version=2.61 X-Spam-Checker-Version: SpamAssassin 2.61 (1.212.2.1-2003-12-09-exp) on servernd.ccl.net This is a copy of a note I sent to Sengen Sun. I am posting it now because there does seem to have been some interest in the issue he raised on CCL - at the time there had been no response. Dr. Sun has promised to respond to my comments in the future. ==================================== Dr. Sun: I noted your request for further response to the "orbital debate" that has arisen from the Nature paper by Villeneuve et al. The orbital model is undeniably a key part of modern electronic structure theory, and it is therefore understandable that experimentalists would seek physical confirmation (if not proof) of its validity. On the other hand, it is equally true that theoreticians have always maintained that orbitals are "merely" mathematical constructs, that any arbitrary set of orbitals does not represent a unique solution to the Schroedinger equation, and that orbitals are therefore non-physical and non-observable. So, to get to the argument over Villeneuve et al: Having read the paper I must confess that I do not fully understand the experiment that they did. They assert that the overtone spectra that they acquire encode symmetry information about the electronic state (which they call an orbital) from which the electron is ejected and to which it returns. Since they cite literature support for this assertion I am prepared to accept it for the sake of argument until someone provides a persuasive counter argument. So, the question is, what did they actually observe and how should it be interpreted? I suggest that denying their experiment on theoretical grounds is scientifically inappropriate. Observation must have priority over theory, or we are talking about religion instead of science. This doesn't mean that they actually observed an orbital - but rather, if you are going to criticise their interpretation of the data you should present an alternative explanation of the origin of their spectra that is consistent with your view of electronic theory as well as with their observations. While the fact that orbitals are "only a model" means we must not assume that they are "real", I suggest that it is inappropriate to take it as axiomatic that the orbital model cannot embody at least some aspect of physical "reality". It is entirely possible that electronic structure behaves under certain specific probes as if orbitals were real, that is, that our artifical model fortuitously captures an observable aspect of electrons. I don't want to argue that Villeneuve et al are correct. But please, if you really want to conduct a scientific debate, address their experimental observations directly and don't simply say that "because they are inconsistent with theory they must be false". Dr. Philip G. Hultin Associate Professor of Chemistry, University of Manitoba Winnipeg, MB R3T 2N2 hultin..at..cc.umanitoba.ca http://umanitoba.ca/chemistry/people/hultin