Energy level cluster analysis for E (ν2) vibration rotation spectrum of spherical top molecules

Abstract
The theory of level clusters, originally developed for ground state (A1) and weakly coupled infrared active (F2, ν3) excited states, is extended to include the Raman‐active (E) states of vibration–rotation. Simple approximate formulas are given for the eigenvalue spectrum of the dominant second order vibration–rotation Hamiltonian and the results are compared with exact computer reductions.