Molecular Symmetry And Group Theory英文电子书.pdf

CHEM 3510 Fall 2003 Molecular Symmetry and Group Theory – The symmetry properties of molecules can be used to: – Reduce the high-order secular determinants in Hückel method – Determine the IR or Raman activity of vibrational normal modes – Label and designate molecular orbitals – Derive selections rules for spectroscopic transitions – The symmetry of a molecule can be described in terms of its symmetry elements. Each symmetry element has symmetry operations (one or more) associated with them. Symmetry elements Symmetry operations Examples Description Symbol Symbol Description ˆ Identity E E No change C2 ˆ Rotation about the axis by n-Fold axis of symmetry Cn Cn C3 360/n degrees C4 ˆ σv σv Plane of symmetry  ˆ ˆ σ σ σ σ  h h Reflection through a plane (mirror plane)  ˆ σd σd ˆ Reflection through the Center of symmetry i i