Dipole moments and charged species



 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.,at,.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