O*

In order to unravel decoherence pathways in a candidate spin qubit system, we measured the vibrational properties of single molecule magnet Na₉[Ho(W₅O₁₈)₂]x35H₂O. We compared our findings with complementary lattice dynamics calculations and models for spin-phonon and vibronic coupling. Magneto-infrared spectroscopy revealed field-induced changes near 63 and 370 cm⁻¹ that we model in terms of f-manifold crystal field excitations activated by odd-symmetry vibrations. These findings advance the understanding of vibronic coupling in molecular magnets, place severe constraints on the spin energy levels in this system, and provide a strategy for designing molecular qubit materials with improved lifetimes.