OODR spectroscopy of BaO. II. New observations of a 3Π and A′ 1Π and re-examination of the Parkinson band system

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Abstract
One and two dye lasers have been used in an optical–optical double resonance (OODR) study of the excited B 1Π and C 1Σ+ states as well as the low‐lying, long‐lived A′ 1Π and a 3Π1 electronic states of BaO. C 1Σ+ (v=0) is shown to be the upper level in the v′=0 progression of the Parkinson band system. Intensity anomalies in C 1Σ+–X 1Σ+ emission, due to an interference effect between parallel and perpendicular transition amplitudes, have proved to be a sensitive indication of ΔΩ=±1 perturbations. Emission from C 1Σ+, which is populated by absorption of two photons via a real intermediate A 1Σ+ vibronic level, into A′ 1Π (v=0,1, and 2) and a 3Π1 (v=0,1, and 2) has been observed. A scheme is presented by which the relative populations of the A′ 1Π and a 3Π ’’reservoir states’’ could be monitored.