A new way of analyzing vibrational spectra. I. Derivation of adiabatic internal modes

✍ Scribed by Zoran Konkoli; Dieter Cremer

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 176 KB
• Volume: 67
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1998)67:1<1::aid-qua1>3.0.co;2-z

✦ Synopsis

A new way of analyzing measured or calculated vibrational spectra in terms of internal vibrational modes associated with the internal parameters used to describe geometry and conformation of a molecule is described. The internal modes are determined by solving the Euler᎐Lagrange equations for molecular fragments n described by internal parameters . An internal mode is localized in a molecular n fragment by describing the rest of the molecule as a collection of massless points that just define molecular geometry. Alternatively, one can consider the new fragment motions as motions that are obtained after relaxing all parts of the vibrating molecule but the fragment under consideration. Because of this property, the internal modes are called adiabatic internal modes, and the associated force constants k , adiabatic force constants. a Minimization of the kinetic energy of the vibrating fragment yields the adiabatic mass n Ž . m corresponding to 1rG of Wilson's G matrix and, by this, adiabatic frequencies . a n n a

Adiabatic modes are perfectly suited to analyze and understand the vibrational spectra of a molecule in terms of internal parameter modes in the same way as one understands molecular geometry in terms of internal coordinates.