The cn1Πuand cn'1Σu+Rydberg states of N2: high resolution studies

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Abstract
Two Rydberg series, cn 1 Pi u from X 1 Sigma g+ and cn' 1 Sigma u+ from X 1 Sigma g+ have been observed in the far absorption spectrum of N2 under high resolution. For n>or=4 it is shown that the 1 Pi u states correspond to the upper levels of the Worley-Jenkins Rydberg series; the cn' 1 Sigma u+ states comprise a new series the first member of which must be considered to be the p' 1 Sigma u+ state. The two sets of states result from the addition of and np Rydberg electron to the X 2 Sigma g+N2+ core. The series run parallel to one another and cn and cn+1' form a 1 Pi u, 1 Sigma u+ pair of states which constitute a p complex. The theory of l uncoupling is applied to these complexes and they are shown to satisfy the condition known as 'accidental pure precession'. Rotational analyses are given for the five complexes from c4-c5' to c8-c9'. Rotational constants, coupling constants and band origins are derived. A marked change in coupling conditions, that is a transition from Hund's case b to case d, is shown to be occurring with increasing n. A strong homogeneous interaction between the c5' 1 Sigma u+ and the b' 1 Sigma u+ states has a pronounced effect on the band structure and prevents a proper l uncoupling analysis of the c4-c5' complex being made. Evidence for a minor degree of homogeneous interaction is found also for the levels of higher n. In addition several small heterogeneous perturbations have been identified.

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