From zoellner.,at,.cacao.issecc.fi.cnr.it Fri Dec 23 06:30:26 1994 Received: from pc1.issecc.fi.cnr.it for zoellner[ AT ]cacao.issecc.fi.cnr.it by www.ccl.net (8.6.9/930601.1506) id FAA19511; Fri, 23 Dec 1994 05:54:10 -0500 From: Message-Id: <199412231054.FAA19511 -A_T- www.ccl.net> To: chemistry%!at!%ccl.net Subject: Dipole moments and charged species Date: Fri Dec 23 10:55:01 1994 Greetings from Firenze! One of my students has asked me a question (really a group of related questions) which has arisen before in my research group, and to which I do not have truly satisfactory answers. Now that I have access to the CCL, I decided to ask it/them of all of you CCL subscribers: 1) Can a species already carrying a charge have a dipole moment as well? 1a) If so, can such a moment (multipole, perhaps?) be calculated in any satisfactory way? 1b) If not, why not? 2) When calculations are carried out on charged species, the result often includes a value for "dipole" moment, yet these values are unreliable. If the "origin" of the ion is changed, with no other changes in bonds, angles, or torsions, the value for the "dipole" can also change. If the origin for charged species was defined as always being at the center of mass, would the resulting value for dipole moment have any validity? 3) Can charge be treated as an "additive" property so that a dipole moment could be calculated for the uncharged species as the structure determined for the charged species, and then adding the extra charge after that? (In other words, making the dipole moment of the charged species the same as the dipole moment for the hypothetical uncharged species?) I have only some general references from the 1930's concerning the determination of quadrupole moments, but nothing more current than that. My apologies to all if these questions seem naive...my students often stump me with seemingly simple ideas which are outside of my areas of so-called "expertise". Thanks in advance for your responses. I shall post a summary of replies. Bob Zoellner zoellner -8 at 8- nauvax.ucc.nau.edu zoellner ^at^ cacao.issecc.fi.cnr.it Robert W. Zoellner, Ph.D.; Associate Professor of Chemistry [currently on sabbatical from Northern Arizona University] ISSECC-CNR; Via Jacopo Nardi, 39; 50132 Firenze; Italy Office telephone: (39-55) 24.59.90 FAX: (39-55) 24.78.366 Home address: Via di Bellariva, 9; 50136 Firenze; Italy Home telephone: (39-55) 67.77.98