Knowledge Bank

A technique recently developed in our laboratory direct ultraviolet absorption spectroscopy of jet-cooled molecules, is used to investigate the second ($\pi ,\pi \ast$) excited states of a series of monosubstituted benzenes: phenylacetylene, styrene, benzaldehyde and acetophenone. The jet spectra exhibit vibronic structure not present in the spectra of these molecules in the gas phase at room temperature or in low temperature matrices. Tentative vibrational analyses of the observed vibronic bands indicate prominent substituent activity in this transition. Implications of these findings for the photophysics and photochemistry of these systems are discussed.