2024ApJ...970...13L

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical region. In this work, the bands of CaCl corresponding to the A²Π - X²Σ⁺ transition with ${v}^{{\prime} }\leqslant $ 4 and v″ ≤ 4, and B²Σ⁺ - X²Σ⁺ transition with ${v}^{{\prime} }\leqslant $ 2 and v″ ≤ 2 are rotationally analyzed with PGOPHER, a multipurpose program for simulating and fitting molecular spectra. All bands were analyzed using high-resolution absorption spectra collected at the National Solar Observatory in 1985, calibrated with atomic lines from a high-resolution emission spectrum obtained in a separate hollow cathode experiment. The results are compared with previous laser-induced fluorescence measurements. Overall, the accuracy of spectroscopic constants for the A²Π and B²Σ⁺ states is improved. Scaled transition dipole moment calculations were used to obtain line strengths. Line lists are provided with Einstein A coefficients and oscillator strengths, which can be used to determine CaCl stellar abundances. Additionally, isotope splittings allowed us to estimate band origins for the ⁴⁰Ca³⁷Cl isotopologue based on band-head positions.