The CaOc3Σ+-a3Πi(0,0) band

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Abstract
Approximately 250 lines of the CaO c 3Σ+-a 3Π (0, 0) band have been resolved using sub-Doppler intermodulation spectroscopy and the principal molecular constants of the c 3Σ+ (23Σ+) state determined. These results will be of particular value to those wishing to use laser induced fluorescence population diagnostics for all six Ω, e/f components of the a 3Π state. Accurate rotational linestrengths for all branches of the c 3Σ+-a 3Π (0,0) transition, computed from eigenvectors of the effective hamiltonians, are presented. Extreme localization of the CaO valence orbitals on either the Ca or the O centre has permitted simple and accurate estimates to be made of fine-structure-determining matrix elements and the locations of unobserved electronic states, including the use of results from CaF to describe the properties of Ca-centred orbitals in CaO. Isoconfigurational second-order spin-orbit arguments, applied to the observed value of the effective spin-spin constant (λ0) for the c 3Σ+ ν = 0 state, lead to confirmed predictions of the previously unknown locations of the E 1Σ- (11Σ-) and e 3Σ- (13Σ-) states and of the value of λ0(e 3Σ-). Assignments are made of nearly all band features in the CaO orange band spectrum.