21A2　U90 - (White Light) Photochemistry

Endstations

The energy or wavelength of this white light branch beam line can be tuned by changing the gap of the U9 undulator; which delivers bright photons with resolution ~2% in the VUV and EUV range. The high performance of this beam line gives the chances for scientists to investigate the photochemistry of molecules and materials in the VUV and EUV region. Two end stations are opened to users currently now.

(A) Matrix-isolation/FTIR system

The end station consists of sample-preparation system, an ultrahigh cryogenic vacuum chamber, and an FTIR spectrometer. A mixed sample gas is deposited onto a cold CsBr window target, which is arranged at 45^o with respect to both the incident SR source and the IR beam axis. The cold target is maintained at 4 K or 10 K in a closed-cycle refrigerator (APD Heliplex HS-4 or HC-DE204S). With a new closed-cycle refrigerator system (Janis RDK-415) capable of cooling the sample target to 3.5 K, we could use not only classical matrix (e. g. Ne, Ar, et al.), but quantum solid (para-hydrogen) as the matrix host. In the detection part, the Bomem DA 8ME FT-IR spectrometer is coupled with the matrix-isolation system to allow us identifying new species generated from photodissociation or photoionization of parent molecules. The FTIR with MCT and InSb detectors spans the IR in range of 500-8500 cm^-1 with max resolution 0.06 cm^-1. The vacuum of the chamber is provided by a 480 l/s turbomolecular pump which in turn is backed by a scroll pump; the pressure is typically less than 1 x 10^-8 Torr.