Specular reflection spectroscopy

See Electron absorption spectroscopy, specular reflectance spectroscopy, diffuse reflectance spectroscopy... 

Figure 9 shows a block diagram of the apparatus for specular reflection spectroscopy. Specular reflection measurements were carried out in conjunction with conventional electrochemical methods the potential was... 

Surface resonance Raman spectroscopy Surface Raman spectroscopy specular reflectance speetroscopy Scanning tunneling microscope Sinface-unenhanced Raman spectroscopy Soft X-ray appearance potential spectroscopy Soft X-ray emission spectroscopy Thermodesorption mass spectroscopy Thermal energy atom scattering Third harmonic generation Thin layer cell... 

Infrared spectroscopy, including Fourier-transform infrared (FTIR) spectroscopy, is one of the oldest techniques used for surface analysis. ATR has been used for many years to probe the surface composition of polymers that have been surface-modified by an etching process or by deposition of a film. RAIR has been widely used to characterize thin films on the surfaces of specular reflecting substrates. FTIR has numerous characteristics that make it an appropriate technique for... 

A powerful characteristic of RAIR spectroscopy is that the technique can be used to determine the orientation of surface species. The reason for this is as follows. When parallel polarized infrared radiation is specularly reflected off of a substrate at a large angle of incidence, the incident and reflected waves combine to form a standing wave that has its electric field vector (E) perpendicular to the substrate surface. Since the intensity of an infrared absorption band is proportional to / ( M), where M is the transition moment , it can be seen that the intensity of a band is maximum when E and M are parallel (i.e., both perpendicular to the surface). / is a minimum when M is parallel to the surface (as stated above, E is always perpendicular to the surface in RAIR spectroscopy). 

Reflection-Absorption IR spectroscopy (RAIRS) where the linearly polarized IR beam is specularly reflected from the front face of a highly reflective sample, such as a metal single crystal surface (Figure 3.1(a)). This is also sometimes referred to as IRAS (IR reflection absorption). The IR beam comes in at grazing angle (i.e. almost parallel to the surface), and although absorption bands in RAIRS have intensities that are some two orders of magnitude weaker than in transmission studies on... 

The most important methods used in in-situ studies of electrode surfaces are various modifications of reflection spectroscopy in the ultraviolet through infrared regions. For electrochemical applications, the specular reflection (at smooth electrode surfaces) is much more important than the diffuse reflection from matt surfaces. The reflectivity, R, of the electrode/ electrolyte interface is defined by ... 

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). 

Specular reflection IR spectroscopy has been used by Cole and coworkers to study the orientation and structure in PET films [36,37]. It has allowed characterizing directly very highly absorbing bands in thick samples, in particular the carbonyl band that can show saturation in transmission spectra for thickness as low as 2 pm. The orientation of different conformers could be determined independently. Specular reflection is normally limited to uniaxial samples because the near-normal incident light does not allow measuring Ay. However, it was shown that the orientation parameter along the ND can be indirectly determined for PET by using the ratio of specifically selected bands [38]. This approach was applied to the study of biaxially oriented PET bottles [39]. 

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. 

For mesitylene and durene, the kinetics have been followed by specular reflectance spectroscopy [159]. The results indicated that mesitylene produces a fairly stable radical cation that dimerizes. That of durene, however, is less stable and loses a proton to form a benzyl radical, which subsequently leads to a diphenylmethane. The stability of the radical cation increases with increasing charge delocalization, blocking of... 

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used to obtain spectra of powders and rough polymeric surfaces such as textiles and paper. IR radiation is focused onto the surface of the sample in a cup resulting in both specular reflectance (which directly reflects off the surface having equal angles of incidence and reflectance) and diffuse reflectance (which penetrates into the sample subsequently scattering in all angles). Special mirrors allow the specular reflectance to be minimized. 

Within the IR spectroscopy arena, the most frequently used techniques are transmission-absorption, diffuse reflectance, ATR, specular reflectance, and photoacoustic spectroscopy. A typical in situ IR system is shown in Fig. 7. Choosing appropriate probe molecules is important because it will influence the obtained characteristics of the probed solid and the observed structure-activity relationship. Thus, the probe molecules cover a range from the very common to the very rare, in order to elucidate the effect of different surfaces to very specific compounds e.g. heavy water and deuter-ated acetonitrile, CDsCN). The design of the IR cell is extremely important and chosen to suit the purposes of each particular study. For catalytic reactions, the exposure of catalytic metals must be eliminated in cell construction, otherwise the observed effect of the catalyst may not be accurate. 

With all its complications and uncertainties, impedance spectroscopy, as seen at the end of the twentieth century, is a growing technique in fundamental electrodic analysis [cf. the seminal contributions of (independently) D. D. and J. R. MacDonald]. Among its advantages is that the necessary equipment is less expensive than that of competing spectroscopic equipment and that it can provide information on any electrochemical situation (e.g., it is not limited by, say, the need for specular reflectance, as in ellipsometry). 

The techniques used in this stage of the work were all IR spectroscopy using a Perkin-Elmer spectrometer 599 and appropriate attachments. Conventional transmission through a sodium chloride cell of path length 0.1 mm, and multiple specular reflectance from aluminium films with a mirror finish were both used. 

Specular and Diffuse Reflectance. Reflectance techniques have been applied primarily to samples which do not permit observation by transmission. Flat surfaces such as those of metal foils and single crystals can he studied by specular reflectance, whereas rough surfaces such as those of powders must be observed by diffuse reflectance. In both cases FT spectroscopy offers strong advantages in terms of the time required to acquire a spectrum. 

Unlike classical analytical spectroscopy performed on liquids or dilute solutions of analytes, diffuse reflectance measurement in the near-infrared must deal with a composite effect of spectroscopic absorption and scattering from the analyte and the matrix in which it is found. Differences in refractive indices of the sample material, specular reflection and observance of relatively small differences are all dealt with in this technique. 

The following summarizes the changes revealed by Specular Reflectance spectroscopy when cotton cloth is heat-aged ... 

Electrode surface derivatization with Id and 4a. In a typical experiment, Au or Pt electrodes of the appropriate size were soaked in a 0.1 mM hexane solution of Id for 24 h. Cyclic voltammetry in CH2C12/Bu4NPF6 solution indicated monolayer coverage (4-8 x 10 10) of Id as did specular reflectance FTIR spectroscopy. The Id treated electrodes were then soaked in a 0.1 M hexane solution of 4a for 15 min. Cyclic voltammetry in CH2C12/Bu4NPF6 indicated that the monolayer formed in this manner consisted of approximately 1 1 ld 4a. 

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