Fourier transform, electromodulated, infrared spectrometer for studies at the electrochemical interface

We report on a newly built infrared spectrometer to be used for vibrational studies at the electrochemical interface. The usual way to select the weak interface absorption consists in changing the electrode potential and measuring the associated change in absorption. However, up to now it was difficult to benefit from both the advantages of using a lock-in detection and Fourier transform spectroscopy. Our apparatus allows simultaneous use of these two techniques. This is achieved by using a slow scan speed (∼6 μm s ^-1) for the Michelson interferometer. The electrode potential may be modulated at a frequency as low as 100 Hz. The ultimate sensitivity of our apparatus corresponds to a relative change of transmitted light intensity of ΔI/I∼10^-6, for a measuring time of 45 min, in the 800-4200 cm^-1 range, with a resolution of 25 cm^-1. Our ultimate resolution capability is 0.5 cm^-1. Data are presented that have been obtained on the n-Si/acetonitrile interface using an attenuated total reflection geometry, which allows further improvement of the performances by one order of magnitude.