On the coupling of ion cyclotron motion to ion internal degrees of freedom

The possibility of significant coupling between gas-phase ion cyclotron motion and two internal angular momentum terms is explored. The first case, coupling with ion spin, is treated via the relativistic Hamiltonian, and found to produce only relativistic perturbations which are entirely negligible. The second case, coupling with ion rotation, is developed via its equivalence to a Stark effect. Small shifts in the cyclotron resonance frequency, ω_c, and the appearanceof a weak-cyclotron resonance at 2ω_c, are predicted, but these effects are negligible in general. If the cyclotron frequency is near an ion rotational transition, however, a shift of 10⁻⁵ in cyclotron frequency may be observed, and could provide a means of investigating low-frequency rotational transitions of ions.