MULTIPLE $n\Pi^{*}$ TRANSITIONS IN TETRAMETHYL–1, 3-CYCLOBUTANEDIONE

Abstract

The polarized single crystal absorption spectrum of the cyclic diketone tetramethyl-1, 3-cyclobutanedione has been obtained in the near ultraviolet region (3700 -- 2600 \AA) at liquid helium temperatures. Four distinct n-$\Pi^{*}$ transitions are observed in the singlet manifold, experimentally verifying the $predicted^{1}$ strong interaction of the carbonyl groups. Spectral assignments have been made, clearly showing that the excited singlet states are distorted from the planar ground state geometry. The band assignments, excited state geometries, and nature of the ``through-bond” interaction will be discussed.