Modulated specular reflectance spectroscopy

Ito et a/.18 supported the above reaction pathways for various cathode materials, such as In, Sn, Cd, and Pb, from the similarity in Tafel slopes. Hori and Suzuki46 verified the above mechanism in various aqueous solutions on Hg. Russell et al.19 also agreed with the above mechanism. Adsorbed CO J anion radical was found as an intermediate at a Pb electrode using modulated specular reflectance spectroscopy.47 This intermediate underwent rapid chemical reaction in an aqueous solution the rate constant for protonation was found to be 5.5 M-1 s-1, and the coverage of the intermediate was estimated to be very low (0.02). 

In order to study the identity and nature of the intermediate, Aylmer-K.elly et al. (1973) employed modulated specular reflectance spectroscopy. They studied the reduction reaction at a lead cathode in both aqueous and non-aqueous electrolytes. A phase-sensitive detection system was employed by the authors, locked-in to the frequency of the potential modulation. The potential was modulated at 30 Hz between the reference potential of — 1.0 V vs. Ag/AgCl and a more cathodic limit. 

When the heterogeneous electron transfer is followed by a chemical step, the registration of spectral data becomes more complicated unless the rate of the chemical reaction is very low. Rapidly reacting species—for instance, radical ions—can be characterized spectroscopically by the application of rapid scan spectroscopy (RSS), modulated specular reflectance spectroscopy (MSRS) and, more recently, diode array spectrometers. 

Figure 50. Visible absorption spectra of the perylene radical anion in DMF containing acetic acid (70 mM) measured by modulated specular reflectance spectroscopy at a, 3 Hz b, 10 Hz c 30 Hz d, 60 Hz and e, 80 Hz. (From Ref. 340.)...

The technique developed by Bewick for use with a dispersive IR spectrometer is termed electrically modulated infrared spectroscopy (EMIRS) and is essentially a direct development of the UV-VIS specular reflectance technique [50], modulated specular reflectance spectroscopy (MSRS). As in MSRS, radiation is specularly reflected form a polished electrode surface while the electrode potential is modulated with a square wave between a base potential and the working potential at which the process of interest occurs the wavelength range of interest is then slowly scanned. Only that... 

In order to avoid the problems coimected with measurement of absolute reflectivities, changes in reflectivity are detected as the potential of the electrode is modulated in the case of the so-called modulated specular reflectance spectroscopy. ... 

Fig. 10.14 - Schematic diagram of the apparatus for modulated specular reflectance spectroscopy.

Bewick, A. and Tuxford, A.M. (1973) Studies of adsorbed hydrogen on platinum cathodes using modulated specular reflectance spectroscopy. Journal ofElectroanalytical Chemistry, 47, 255-264. 

When Desilvestro and Pons used in situ IR reflection spectroelectrochemistry to observe the reduction of C02 to oxalate at Pt electrodes in acetonitrile [83], two different forms of oxalate were observed. Similarly, Aylmer-Kelly et al. studied C02 reduction in acetonitrile and propylene carbonate at Pb electrodes [84], by using modulated specular electroreflectance spectroscopy. Subsequently, two radical intermediates were observed which they determined to be the C02 radical anion, C02, and the product of the radical anion and C02, the (C02)2 adduct (see Equations 11.9 and 11.10). Vassiliev et al. also studied the reduction of C02 in... 

Specular reflection spectroscopy has been actively used in in situ studies of the formation and optical behaviour of monolayer films on surfaces, and for detecting intermediates and products of heterogeneous chemical and electrochemical reactions. The vibrational spectra of the adsorbed species at electrode surfaces are obtained by surface-enhanced Raman scattering and infrared reflectance spectroscopies. Since the mid-1960s, modulated reflection spectroscopy techniques have been employed in elucidating the optical properties and band structure of solids. In the semiconductor electroreflectance, the reflectance change at the semiconductor surface caused by the perturbation of the dielectric properties of... 

Specular reflection spectroscopy enables us to study the redox behaviour of adsorbed species at a mirror electrode when either or both oxidized and reduced forms of the adsorbed species exhibit strong absorption bands in the UV-Vis region. In this case, the mode of measurement is, in fact, the absorption spectra of the adsorbed species at the electrode surface [55]. The potential modulated reflectance spectrum of the adsorbed molecules in the vicinity of its formal potential is given by the following equation ... 

Investigation of the mechanical, adhesion, and electrical behavior of ultrathin polymer films requires spatial resolution of the order of 10-100 °A. Specular reflectance spectroscopy is a most convenient technique for probing structures on either metallic or dielectric surfaces. Furthermore, techniques such as polarization modulation spectroscopy have significantly increased sensitivity and the possibility of photoacoustic spectroscopy is also available. 

The existence of various hydrogen species on platinum, palladium, and iridium surfaces has also been verified by in situ modulated specular and internal reflection spectroscopy and surface conductance measurements... 

---