The effect of solvation on molecular Rydberg states: Dioxane clustered with nonpolar solvents

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Abstract
One color 2+1 mass resolved excitation spectroscopy is employed to obtain molecular Rydberg 3s←n transition spectra of 1,4-dioxane clustered in a molecular beam with nine nonpolar solvents. The solvents are Ar, Kr, CH4, CD4, CF4, SiH4, Si(CH3)4, ethane, n-propane, cyclohexane-h12, and cyclohexane-d12. Spectral results are interpreted in terms of cluster size, isotope effects, and model calculations. A Lennard-Jones–Coulomb 6-12-1 potential is used to model the intermolecular interactions and predict minimum energy cluster geometries, cluster binding energies, and intermolecular force constants which are used to calculate van der Waals vibrational frequencies. The results show that for simple solvents (i.e., Ar, CH4) the calculations offer a simple interpretation of the observed spectra in terms of multiple cluster geometries with distinct transition energies; however, as the solvent becomes more complex, the cluster spectra also become more complex, and the number of calculated minimum energy cluster geometries increases. Complex spectra are interpreted as a distribution of cluster geometries with similar transition energies. For all of the clusters, the electronic origins are blue shifted with respect to the bare 1,4-dioxane origin. This observation is consistent with a model in which the excited state intermolecular potential becomes more repulsive due to the increased radial distribution of a nonbonding electron upon excitation into the 3s Rydberg state.

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