From chemistry-request@server.ccl.net Thu Jul 20 04:52:27 2000 Received: from smtprelay.ruc.dk (smtprelay.ruc.dk [130.225.220.22]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id EAA05250 for ; Thu, 20 Jul 2000 04:52:26 -0400 Received: from virgil.ruc.dk (virgil.ruc.dk [130.225.220.110]) by smtprelay.ruc.dk (8.9.3/8.9.3) with ESMTP id KAA24738 for ; Thu, 20 Jul 2000 10:44:51 +0200 (MET DST) Received: from VIRGIL/SpoolDir by virgil.ruc.dk (Mercury 1.44); 20 Jul 00 10:43:18 +0100 Received: from SpoolDir by VIRGIL (Mercury 1.44); 20 Jul 00 10:43:12 +0100 From: "Jens Spanget-Larsen" Organization: Roskilde Universitetscenter To: CHEMISTRY@ccl.net Date: Thu, 20 Jul 2000 10:43:01 +0100 Subject: CCL: Seeing molecular orbitals? Priority: normal X-mailer: Pegasus Mail for Windows (v2.23) Message-ID: <92CE6BB1672@virgil.ruc.dk> Dear CCL: In a recent, most interesting publication ('Seeing molecular orbitals', Chem.Phys.Letters 321, 78-82 [2000]) scanning tunneling microscopy is used to observe the shapes of single molecular orbitals of the fullerene C60: "..the scanning tunneling microscope (STM) is probing a single molecular orbital (MO)." However, this reminds me of previous statements in the literature some time ago, associated with the advent of molecular photoelectron spectroscopy, f.i. "Chemists can see the orbital structure of even fairly large molecules and no longer have to rely on the predictions of theoreticians" "Photoelectron spectroscopy has demonstrated experimentally to chemists, physicists and other sceptics that molecular orbitals really do exist" I wonder whether this is acceptable terminology, considering the fact that molecular orbitals are model constructs; they are not physical observables. By using approximations, such as Koopmans' approximation, many experimental observations can be conveniently interpreted in terms of theoretical MO data. But strictly speaking, this does not turn MOs into observable quantities; MOs have no physical existence. Any comments? Yours, Jens >--< =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= JENS SPANGET-LARSEN Phone: +45 4674 2000 (RUC) Department of Chemistry +45 4674 2710 (direct) Roskilde University (RUC) Fax: +45 4674 3011 P.O.Box 260 E-Mail: JSL@virgil.ruc.dk DK-4000 Roskilde, Denmark http://www.rub.ruc.dk/dis/chem/psos/ =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=