Potential-difference infrared

In this study, adsorption of acetic acid under voltammetric conditions was observed by a vibrational technique for the first time. The first work in the field was carried out using FTIR (potential difference infrared spectroscopy, PDIRS) and by radioactive labeling [Corrigan et al., 1988]. Both techniques... 

Figure 2.50 Potential difference infrared (PDIR) spectra for adsorbed azide at the silver-aqueous interface in the asymmetric N-N-N stretch region. The reference (base) potential was -970 mV vs. SCE sample potentials as indicated. The solution contained 0.01 M NaNj/0.49 M NaCI04. The spectra are the average of 1024 interferometer scans at each potential. From Corrigan and Weaver (1986), Copyright 1986 American Chemical Society.

Potential-difference infrared (PDIR) spectra for adsorbed azide at an electrochemlcally roughened silver-aqueous interface in the asymmetric N-N-N, i/aB, stretch region. Electrolyte 0.01 JJ... 

The same method is sometimes called PDIRS (for potential difference infrared spectoscopy) or SPAIRS (for single potential alteration infrared spectroscopy). 

LPSIRS Linear Potential Sweep Infra-Red Spectroscopy SPAIRS Single Potential Alteration Infra-Red Spectroscopy PDIRS Potential Difference Infrared Spectroscopy EMIRS Electrochemically Modulated Infra-Red Spectroscopy SERS Surface Enhanced Raman Scattering (Surface Enhanced Raman Spectroscopy)... 

The tremendous advances that have occurred in the spectroscopic analysis of the electrode/electrolyte interface have begun to provide a fundamental understanding of the elementary processes and the influence of process conditions. Surface-sensitive spectroscopic and microscopic analyses such as surface-enhanced Raman scattering (SERS) [1], potential-difference infrared spectroscopy (PDIRS) [2], surface-enhanced infrared spectroscopy (SEIRS) [3], sum frequency generation (SFG) [4], and scanning tunneling microscopy (STM) [5,6] have enabled the direct observation of potential-dependent changes in molecular structure [2,7] chemisorption [8,9], reactivity [10], and surface reconstruction [11]. 

Figure 1. Plots of surface concentration versus potential for ImM acetic acid from radiochemistry measurements ( ) and for lOmAf acetic acid from potential-difference infrared spectroscopy (o) at a platinum electrode in aqueous 0. IM HCIO4. (Adapted from Corrigan et al.)...

Fig. 9 Potential-difference infrared spectra in a CO-saturated 0.1 M HCi04 soiution at (a) -0.01 V and (b) 0.34 V versus RHE, reference was made by stepping to 0.75 V RH E [35].

Reaction products can also be identified by in situ infrared reflectance spectroscopy (Fourier transform infrared reflectance spectroscopy, FTIRS) used as single potential alteration infrared reflectance spectroscopy (SPAIRS). This method is suitable not only for obtaining information on adsorbed products (see below), but also for observing infrared (IR) absorption bands due to the products immediately after their formation in the vicinity of the electrode surface. It is thus easy to follow the production of CO2 versus the oxidation potential and to compare the behavior of different electrocatalysts. 

Cutlip and Kenney (44) have observed isothermal limit cycles in the oxidation of CO over 0.5% Pt/Al203 in a gradientless reactor only in the presence of added 1-butene. Without butene there were no oscillations although regions of multiple steady states exist. Dwyer (22) has followed the surface CO infrared adsorption band and found that it was in phase with the gas-phase concentration. Kurtanjek et al. (45) have studied hydrogen oxidation over Ni and have also taken the logical step of following the surface concentration. Contact potential difference was used to follow the oxidation state of the nickel surface. Under some conditions, oscillations were observed on the surface when none were detected in the gas phase. Recently, Sheintuch (46) has made additional studies of CO oxidation over Pt foil. 

The technique using p-s modulation has received different names depending on the kind of IR instrument used. Thus for grating instruments it was called PMIRRAS (polarization modulation infrared reflection-absorption spectroscopy) [6]. For FT spectrometers the name FTIRRAS [8] was suggested. However this name was later used also in connection with Fourier transform spectra applying the potential difference approach. 

As shown in Table 25-2 (p. 761), four types of thermal detectors are used for infrared spectroscopy. The most widely used is a tiny thermocouple or a group of thermocouples called a thermopile. These devices consist of one or more pairs of dissimilar metal junctions that develop a potential difference when their temperatures differ. The magnitude of the potential depends on the temperature difference. 

A well-designed thermocouple transducer is ca pable of responding to temperature differences of 10 K, This difference corresponds to a potential difference of about 6 to S pV/pW. The thermocouple ol an infrared detector is a low-impedance device that is... 

PDFTIRRAS Potential difference Fourier transform infrared reflection absorption spectroscopy... 

Subtractively Normalized Fourier Transform Infrared Spectroscopy and Potential Difference I nfrared Spectroscopy In... 

This equation states that a quantum of light with wavelength 1240 nm (in the near infrared) has the same energy as an electron that has been accelerated by a potential difference of 1 volt. This energy quantity is sometimes called 1 electron volt, with abbreviation 1 eV. 

---