Characterisation of a new VUV beamline at the Daresbury SRS using a dispersed fluorescence apparatus incorporating CCD detection

The design and performance of a new normal incidence monochromator at the Daresbury Synchrotron Radiation Source, optimised for experiments requiring high flux of vacuum-UV radiation, are described. The re-developed beamline 3.1, based on the Wadsworth design of monochromator, is the source of tunable vacuum-UV photons in the range 4 – 31 eV, providing over two orders of magnitude more flux than the vacuum-UV, Seya monochromator in its previous manifestation. The undispersed and dispersed fluorescence spectra resulting from photoexcitation of N$_2$, CO$_2$, CF$_4$ and C$_6$F$_6$ are presented. Emitting species observed were N$_2^+$ B$^2\Sigma_u^+$ - X$^2\Sigma_g^+$, CO$_2^+$ A$^2\Pi_u$ - X$^2\Pi_g$ and B$^2\Sigma_u^+$ - X$^2\Pi_g$, CF$_4$$^+$ C$^2$T$_2$ - X$^2$T$_1$ and C$^2$T$_2$ - A$^2$T$_2$, CF$_3$* $^2$A$^’_2$ - $^2$A$^”_2$, and C$_6$F$_6^+$ B$^2$A$_{2u}$ - X$^2$E$_{1g}$. A CCD multi-channel detector has significantly reduced the time period needed to record dispersed fluorescence spectra with a comparable signal-to-noise ratio