Vibronic Spectroscopy of Sympathetically Cooled CaH

We report the measurement of the 1¹ Σ→2¹ Σ transition of CaH⁺ by resonance-enhanced photodissociation of CaH⁺ that is co-trapped with laser-cooled Ca⁺ . We observe four resonances that we assign to transitions from the vibrational v=0 ground state to the v'=1-4 excited states based on theoretical predictions. A simple theoretical model that assumes instantaneous dissociation after resonant excitation yields results in good agreement with the observed spectral features except for the unobserved v'=0 peak. This discrepancy is attributed to an insufficient understanding of the dissociation process, and further experimental and theoretical studies are required to confirm the assignment. The resolution of our experiment is limited by the mode-locked excitation laser, but this survey spectroscopy enables future rotationally resolved studies with applications in astrochemistry and precision measurement.