SNIFTIRS subtractively normalised

The introduction of in-situ infrared spectroscopy to electrochemistry has revolutionised the study of metal/electrolyte interfaces. Modnlation or sampling techniques are applied in order to enhance sensitivity and to separate snrface species from volume species. Methods such as EMIRS (electrochemicaUy modulated IR spectroscopy) and SNIFTIRS (subtractively normalised interfacial Fonrier Transform infrared spectroscopy) have been employed to study electrocatalytic electrodes, for example. There have been surprisingly few studies of the semiconductor/electrolyte interface by infrared spectroscopy. This because up to now little emphasis has been placed on the molecnlar electrochemistry of electrode reactions at semiconductors because the description of charge transfer at semiconductor/electrolyte interfaces is derived from solid-state physics. However, the evident need to identify the chemical identity of snrface species should lead to an increase in the application of in-situ FTIR. 

SNIFTIRS subtractively normalised interfacial Fourier transform iirfrared spectroscopy... 

Pons and co-workers [79] reported the first potentially modulated in-situ FTIR studies of the near-electrode region and they then developed the technique [24, 55, 56, 69] and eventually coined the acronym SNIFTIRS (subtractively normalised interfacial Fourier transform infrared spectroscopy). Corrigan et al. [81-83] and Bockris and co-workers [80, 84-88] have also reported studies employing the technique, or variations on it. These techniques all employ some form of potential modulation regime as with EMIRS, intended to cancel out all those absorptions that do not change with potential (bulk solvent, window, etc.), the spectra are again presented as (AR/R)v vs. v. However, the stepwidths (i.e. the time spent at each potential) in a SNIFTIRS experiment are much longer than those in EMIRS several tens of seconds instead of a tenth of second [89, 90]. 

Both these concerns were addressed by the development of modified IR techniques. In the technique of Subtractively Normalised Fourier Transform IR Spectroscopy (SNIFTIRS) or Potential Difference IR (SPAIRS or PDIR) [37], the increased stability and sensitivity of Fourier Transform IR is exploited, allowing usable spectra to be obtained by simple subtraction and ratioing of spectra obtained at two potentials without the need for potential modulation or repeated stepping. A second technique which does not call for potential modulation, but actually modulates the polarisation direction of the incoming IR beam is termed Photo-elastically Modulated Infra-Red Reflectance Absorption Spectroscopy (PM-IRRAS) this was applied to the methanol chemisorption problem by Russell and co-workers [44], and Beden s assignments verified, including the potential-induced shift model for COads. 

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