ASSIGNMENT OF THE LOWEST $^{3}\Pi$ AND $^{1}\Pi$ STATES OF CaO, SrO, AND BaO

Abstract

New techniques for the assignment of perturbations in electronic spectra are applied to perturbations in the $A^{1}\Sigma - X^{1}\Sigma$ bands of CaO, SrO, and BaO. These techniques utilize observed perturbation matrix elements to establish electronic and vibrational assignments of perturbing states. Using only data reported by Lagerqvist and co-workers between 1949 and 1951, it has been possible to assign perturbations of $A^{1}_{3}\Sigma^{+}$ state to a $^{1}\Pi$ state ($A^{\prime}^{1}\Pi$) and to three components of an inverted $^{3}\Pi$ state ($a^{3}\Pi_{i}$). Absolute vibrational assignments have been made and the following spectroscopic constants obtained (in $cm^{-1}$ with one standard deviation uncertainty in the last digit in parentheses). [FIGURE] The $A^{\prime}\Pi - a^{3}\Pi$ energy separations are small, and the $a^{3}\Pi$ state, the lowest state which dissociates to ground state atoms, lies at surprisingly high energy. The $X^{1}\Sigma^{+}$ state is now proven to be the ground state of BeO, MgO, CaO, SrO, and BaO