The FTIR spectroscopy system (model Cary 660, online manual) was purchased from Agilent, currently a branch of Bruker Corp., and allows conventional absorption and transmission measurements using the internal DLaTGS (deuterated L-alanine doped triglycene sulphate) detector. This unit operates at the wavenumber range of 4000 to 400 cm^-1 (2.5 - 25 μm) and measurements of photocurrent can also be performed by replacing the internal detector accordingly. An optical N₂ or He cryostat can be used for measurements at cryogenic temperatures between 12 and 300 K.