Gas phase electronic spectra of xylene-water aggregates

Using a jet spectroscopy molecular beam setup, gas phase electronic spectra of three xylene isomers (para, meta and ortho) have been collected for the neutral monomer species as well as for their clusters with one and two water molecules. Scans at a resolution of ±0.02 nm showed a clear 0–0 transition for each xylene isomer as well as the vibronic progression. The spectra were assigned with the help of Franck–Condon factor PGOPHER simulations from theoretical studies at the CAM-B3LYP/aug-cc-pVDZ level of theory. The vibronic spectra of the xylene$\cdot$H${}_2$O and xylene$\cdot$(H₂O)₂ clusters showed broad features between 36800–38400 cm⁻¹ (260–272 nm) for p- and m-xylene, while the water clusters of o-xylene gave more defined bands. The separation of the vibronic bands in the clusters mirrors the progression of the neutral monomers implying that, for the S₁ $\leftarrow$ S₀ transition, it is the same vibrational modes that are involved in the monomer as in the clusters with water. Both the separation and the spectral width of the bands can be explained by the calculated differences in geometries of the clusters in the ground and first electronic excited states.