Knowledge Bank

Combination of the data obtained by resonant multiphoton ionization and electron impact spectroscopies has been exploited to enable Rydberg and valence transictions to be experimentally distinguished and to permit optically forbidden transitions to be located. The technique was verified on 2,3--dimethylbutadiene, whose transitions could characterized by electron impact results alone, and then applied to seven internally and externally methyl substituted dienes in both the s-cis and s-trans configurations. It was possible to locate the $NV2(Ag)$ transition in 6 of the studied molecules. The effect of Symmetry and methyl substitution on the valence and Rydberg transitions of these will be discussed.