Vacuum-UV fluorescence spectroscopy of polyatomic molecules

Experiments are described in which UV and visible fluorescence is observed following vacuum-UV photoexcitation of a range of polyatomic molecules in the gas phase. Tunable radiation in the energy range 8–25 eV from synchrotron sources at Daresbury, UK and BESSY 1, Germany is used as the photoexcitation source. Non-dispersed fluorescence excitation spectra and dispersed fluorescence spectra are recorded at Daresbury and BESSY 1, respectively. The experiments are sensitive to Rydberg states of molecules that photodissociate to an excited state of a fragment that fluoresces, and to valence states of the parent molecular ion that fluoresces. Using single-bunch mode of BESSY 1, lifetimes of the emitters in the range ca. 3–100 ns are measured. Examples are taken from work either published or in press in SiF4 and GeF4, PF3, MCl4 (M=C, Si, Ge), and CXCl3 (X=H, F, Br).