Causes of l-Type Doubling in the 3p(E″) Rydberg State of Ammonia

Abstract

Expressions are developed for the rotational levels of an electronically degenerate planar XY₃ molecule. It is shown that there can be strong l‐type doubling only in levels with no vibrational angular momentum and that this doubling has two main causes, namely, a rotational—electronic interaction and a rotational—Jahn—Teller interaction. The l‐type doubling of other levels is largely quenched by vibronic coupling. Estimates of the observed l‐type doubling in the 3p(E″) state of ammonia indicate that the two above contributions act in opposite senses. A mechanism which accounts for the variation of the observed l‐type doubling with vibronic state is suggested.