Knowledge Bank

Acetaldehyde molecules in the first singlet excited state contain two coupled low frequency vibrational modes, $\nu 14$ (inversion) and $\nu 15$ (torsion). In an earlier paper, a two dimensional least squares analysis of the first seven bands in the UV spectrum of acetaldehyde jet-cooled vapor gave an excited state barrier to inversion of $585.13cm-1$ and a torsional barrier of $721.43cm-1$. A discussion of the results of a vibrational and rotational analysis of 12 additional bands beyond this earlier analysis will be presented. The assignment of the $1402$ band has changed and the inclusion of the higher members of the torsional mode has given refined values for the barriers.