van der Waals broadening of the X̃→B̃ (3s Rydberg) transition of acetone by He, Ar, and CH4: Inversion of the spectra to the interaction pair potentials

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Abstract
The X̃→B̃ absorption spectrum of acetone at 1944 Å, corresponding to the transition to the (n0,3s) Rydberg state, has been measured in the presence of moderate pressures of the perturbers Ar, CH4, and He. The line shape changes, which are ascribed to van der Waals perturbations, are analyzed globally using an iterative Fourier transform technique. This method is successful in inverting the distorted spectra into Lennard‐Jones (6‐12) potentials for the ground and excited acetone–perturber van der Waals complexes (for Ar and CH4), and into a (6‐12) potential for the ground state and a repulsive potential for the excited state of the acetone–He complex. For Ar and CH4, optimized ground state (6‐12) parameters are consistent with those obtained with simple combining rules; in these cases, the excited state parameters show that the interaction distance is larger than that for the ground state by ∼0.37 and 0.35 Å, respectively, and that the well depth is smaller by ∼42 and 33 cm−1, respectively. The results with He indicate that a repulsive potential is needed to describe the excited state–perturber interaction.

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