Photodissociation spectroscopy of $Al+$-acetaldehyde

We have investigated the photodissociation spectroscopy of the $Al+$-acetaldehyde bimolecular complex over the spectral range 212–345 nm. We find evidence for three overlapping molecular absorption bands in the near UV. Two of the bands are unstructured and are assigned as $1A″$ and $2A″←1A′.$ These continuum bands are of mixed character with contributions from $Al+$-centered $3pπ(A″)←3sσ(A′),$ acetaldehyde-centered $π*(A″)←n(A′),$ and Al-acetaldehyde charge transfer excitation processes. The third absorption band at short wavelengths, $λ>223 nm,$ shows a prominent vibrational progression with a mode frequency $ωe=210±4 cm−1.$ The structured band is assigned as $2A′←1A′$ and correlates to an $Al+$-centered $3pπ(A′)←3sσ(A′)$ radiative transition; the vibrational progression is assigned to the intermolecular $Al+$-acetaldehyde in-plane bend. Spectroscopic results are in good agreement with ab initio predictions.