A NEW LOOK AT NORMAL COORDINATE CALCULATIONS

Author Institution: Chemistry Division, Argonne National Laboratory; Department of Chemistry, University of MissouriFor normal coordinate calculations done by means of a computer, it is suggested that Cartesian coordinates are more convenient than the usual internal coordinates. A calculation procedure for normal coordinates and frequencies is outlined that makes no use of symmetry coordinates, and is therefore particularly convenient for calculations involving isotopic substitutions. The problem of expressing the potential energy of a molecule in terms of a Cartesian basis is discussed in detail for the orbital valency force field model for molecules of the type, $XY_{n}$