Spin-dependent interactions for linear molecules in Σ states of quartet and higher multiplicity

The form of the effective hamiltonian for the rotational levels of linear molecules in Σ states of high multiplicity (2S + 1 ⩾ 4) has been investigated. The explicit operator form for some higher-order spin-spin and spin-rotation interactions has been established and the determinable parameters related to the relevant matrix elements. Order of magnitude considerations suggest that the requirement of two spin-rotation parameters in the description of a 4Σ state, although rigorously correct, is not likely to be necessary except in measurements of the highest precision.