s and d Rydberg complexes of NO probed by double-resonance multiphoton ionisation in the regionn* = 5 ton* = 25; multichannel quantum defect analysis. Part II

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Abstract
Optical-optical double-resonance multiphoton ionisation spectroscopy is used to probe the n*s and n*d Rydberg series converging to the first rotational levels of NO+X1Σ+, v = 0. Intermediate values of the principal quantum number probed are 5 ⩽ n* ⩽ 2>5. The initial excitation occurs via one of two rotational-parity levels of the C 2Π state (N′ = 2 and N′ = 6). A description of the rotational-electronic structure of the observed supercomplexes is proposed in terms of multichannel quantum defect theory (MQDT). The observation of ‘forbidden’ n*f levels is tentatively explained both in terms of d-f mixing in the upper levels and of a d-wave contribution to the 3pπ orbital of the C state. Rydberg-valence interactions show up as predissociation, which strongly competes with ionisation in the intermediate n*d supercomplexes with 8 ⩽ n* ⩽ 1>2. This work complements the previous analysis of the s and d Rydberg states of NO corresponding to n* ⩽ 8> and 25 ⩽ n* ⩽ 4>0 [15].