The
and
states of SrOH were investigated using optical–optical double-resonance (OODR) spectroscopy. Rotational and fine structure parameters have been determined for these two states through a combined least-squares fit of the current OODR data along with the OODR data of the
transition, the optical data of the
transition and the millimeter-wave pure rotational measurements of the
state. The spin–rotation constant,
γ, of the
state was found to be 0.002653 cm
−1, which is two orders of magnitude smaller than that of the
state (−0.1447 cm
−1). This small
γ value suggests that this state arises from a Sr
+ atomic orbital of mainly 6
sσ character. This atomic orbital assignment is also supported by the large rotational constant observed in the
state and the similarity of the molecular constants to those of the
state of CaOH. The rotational energy levels of the
state of SrOH were found to be largely perturbed, which prohibited the accurate determination of the spin–rotation constant in this state. This perturbation is most likely due to an interaction with a
2Σ vibronic component of the nearby
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