Rotational energy levels of symmetric top molecules in 2 E states

Expressions are derived for the rotational energy levels of a symmetric top molecule in a ² E state which take into account a spin-orbit interaction and vibronic Jahn-Teller interactions. Some group theoretical aspects of the Jahn-Teller problem for a general symmetric top molecule are discussed. In addition, the overall selection rules and formulae for the relative intensities of rotational lines in a ² A-² E transition are derived and the possibility of applying them to two recently published experimental examples is considered.