A Thermo Nicolet 6700 FTIR spectrometer, controlled with OMNIC 7.3 SP1 (Thermo Scientific) software, was used to record FTIR spectra. Liquid samples were held in a Thermo HT-32 demountable cell with CaF2 windows (Thermo Scientific) and a copper or lead spacer between the windows (usually a 0.025 mm copper spacer). 40 µl of liquid sample was injected into the cell. A background air spectrum, using an empty sample compartment (no cell), was recorded just before a sample was analysed. Spectra consist of 32 scans recorded at a resolution of 4 cm -1 . Spectra were collected at room temperature, with the cell temperature measured with a Thermo Scientific CAL 9500 thermostat.