High resolution laser spectroscopy of free radical-inert gas complexes: C5H5⋅He, C5H5⋅He2, C5H5⋅Ne, and CH3–C5H4⋅He2

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Abstract
Several inert‐gas complexes of the free radical cyclopentadienyl and its methyl derivative (C5H5⋅He, C5H5⋅Ne, C5H5⋅He2, and CH3–C5H4⋅He2, and CH3–C5H4⋅He) have been studied at low temperature via their laser induced fluorescencespectra in a supersonic free jet expansion. The rotational structures of the near‐uv electronic transitions of the radicals have been resolved and analyzed. These analyses lead to precisely defined geometries for the radicals. In contrast to inert‐gas, closed‐shell aromatic complexes, the inert‐gas radical ring bond lengths are found to be strongly dependent upon electronic state and methyl substitution. Additional molecular parameters were measured in the complexes including the electronic angular momentum, the (2,2) interaction parameter for the C5H5 complexes, and for the methyl derivative, the barrier to methyl rotation. These are compared to their values in the uncomplexed radicals.