Equipment and Methods

Absorption:

For a description of our experimental procedure for acquiring absorption spectra, please refer to our online summary (opens in a new window).

Reflectivity:

IR reflectivity spectra were acquired at near-normal incidence using a Spectratech Fourier transform IR spectrometer (Spectra-Tech Inc., Stamford, CT, USA) microscope and using an evacuated Bomem DA 3.02 Fourier transform spectrometer (Bomem Inc., Quebec, Canada) at 1 or 2 cm^-1 resolution. The accuracy of the instrument is ~ 0.01 cm^-1. An Si-bolometer and a coated mylar beamsplitter were used for the far-IR range from ~ 50 to 650 cm^-1 (~ 23-21.5 microns). A CaF₂ beamsplitter and an InSb detector were used for the near-IR from ~ 1800-8500 cm^-1 (~ 6-12 microns). An SiC source was used for these IR regions. A quartz source, an Si avalanche detector and a quartz beamsplitter probed the visible region of ~ 8500 to 20 000 cm^-1 (~ 1.2-0.45 microns). A gold mirror was used as the reference for the far- and mid-IR, and silver for the near-IR and visible regions. The number of scans ranged from 800 to 2000.