sshade:databases:acid:instruments [SSHADE]

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===== ACID instruments, techniques and cells =====

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=== Spectroscopic instruments, techniques and cells ===

**VUV Experiments**

The VUV spectra were measured at the National Synchrotron Radiation Research Center (NSRRC), Taiwan. VUV photons from the beamline were focused on a lithium fluoride (LiF) window, kept at 10 K, that was enclosed in a vacuum chamber at pressures on the order of 10^−8 mbar. The vapor from a liquid sample (from commercial sources) was then allowed to form a uniform film on a LiF substrate. Spectra (107–320 nm; 11.6–3.8 eV) were accumulated before and after deposition to obtain the incident (Io) and transmitted (It) intensities from which absorbance spectra of the ice films were derived are calculated using the Beer–Lambert law. 

The temperature dependence of the VUV spectra were recorded by annealing the sample to higher temperatures, until sublimation. The minimum wavelength cut off (107 nm; 11.6 eV) in these spectra was determined by the window material used (LiF) as both the entrance and substrate window. 

**IR Experiments**

The IR spectra were all carried out in experimental system in PRL, NSRRC and OU. Molecules in the condensed phase are probed using Fourier Transform InfraRed spectroscopy operating mainly in the Mid-IR range (4000 cm^-1 - 400 cm^-1). Though data were obtained in different experimental facilities, the main components of the experimental chamber were a cold head (closed-cycle helium cryostat) with a sample mount that can reach temperatures as low as 10 K while the chamber pressure was on the order of 10^−10 mbar (obtained using the combination of turbo- and dry-backing pumps). 

Molecules were condensed onto a IR substrate, zinc selenide (ZnSe) / potassium bromide (KBr), attached to the sample mount with the temperature at the substrate controlled using a combination of a Si diode sensor and ultrahigh vacuum (UHV) heater looped to a temperature controller.