THE 1790 \AA TRANSITION OF 2-METHYLPROPENE (ISOBUTENE)

Abstract

The vibronic structure of the absorption system originating around 1795 \AA in 2-methylpropene (isobutene) has been studied for the parent compound and for three symmetrically deuterated isomers. In addition to the sequences previously $reported,^{1}$ progressions are observed in the $C = C$ stretch, $-CH_{3}$ symmetric deformation, $=CH_{2}$ deformation, $=CH_{2}$ torsion and $-CH_{2}$ torsion vibrational modes. The observed origin is tentatively identified as a false origin. By elimintion, the transition is deduced to be $A_{2}\sigma_{{C-C}}$ ($P_{y}$, $b_{2}) \leftrightarrow (p_{x}, b_{1}$). Insufficient information is available to assign the transition more completely.