Optical-optical double resonance spectroscopy of the D˜2Σ+-A˜2Πtransition of CaOH

The D˜2Σ+ state of CaOH was investigated using optical-optical double resonance spectroscopy. A combined least-squares fit of the D˜2Σ+-A˜2Π double resonance transition data along with A˜2Π-X˜2Σ+ optical transition data and the millimeter-wave pure rotational data of the X˜2Σ+ state was performed using an effective Hamiltonian. The spin-rotation constant was determined for the D˜2Σ+ state for the first time. An analysis of these constants showed that the Ca-O bond length and spin-rotation parameter of the D˜2Σ+ state have the smallest values of all the observed 2Σ+ states of CaOH. This evidence suggests the assignment of the D˜2Σ+ state as arising from a Ca+ atomic orbital of mainly 5sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.