ANOMALOUS STRUCTURE IN THE A 6-SIGMA+-X6-SIGMA+ TRANSITION OF MNO CAUSED BY INTERFERENCE BETWEEN 2 INTERNAL HYPERFINE PERTURBATIONS

{Sub-Doppler spectra of the A 6-SIGMA+ - X 6-SIGMA+ electronic transition of gaseous MnO are reported. It is found that both electronic states contain "internal hyperfine perturbations" where the hyperfine levels of different electron spin components interact through matrix elements of the hyperfine Hamiltonian off-diagonal in the quantum number J. The nu = 0 level of the A 6-SIGMA+ state is severely perturbed by another electronic state so that its internal hyperfine perturbations are overwhelmed; in consequence the A-X (0, 0) band shows a characteristic pattern of line doublings, resulting from the internal perturbations of the X 6-SIGMA+ state alone. The A 6-SIGMA+