Precise Determination of Excited State Rotational Constants and Black-Body Thermometry in Coulomb Crystals of Ca+ and CaH+
Abstract
We present high-resolution rovibronic spectroscopy of calcium monohydride molecular ions (CaH+) co-trapped in a Coulomb crystal with calcium ions (40Ca+), focusing on rotational transitions in the |X1+, " = 0> → |A1+, ' = 2> manifold. By resolving individual P and R branch transitions with record precision and using Fortrat analysis, we extract key spectroscopic constants for the excited state |A1+, ' = 2>, specifically, the band origin, the rotational constant, and the centrifugal correction. Additionally, we demonstrate the application of high-resolution rotational spectroscopy of CaH+ presented here as an in-situ probe of local environmental temperature. We correlate the relative amplitudes of the observed transitions to the underlying thermalized ground-state rotational population distribution and extract the black-body radiation (BBR) temperature.
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