Polarization modulated infrared

I. Noda, A.E. Dowrey and C. Marcott, Characterization of polymers using polarization-modulation infrared techniques Dynamic infrared linear dichroism (DIRLD) spectroscopy. 

The three most commonly applied external reflectance techniques can be considered in terms of the means employed to overcome the sensitivity problem. Both electrically modulated infrared spectroscopy (EMIRS) and in situ FTIR use potential modulation while polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) takes advantage of the surface selection rule to enhance surface sensitivity. 

Vibrational spectra were recorded using the polarization-modulated infrared reflection absorbance technique (PM-IRRAS). The spectrometer, the electrochemical cell, and the sample preparation and cleaning procedures are all described elsewhere (1 7) All of the measurements were performed using 0.5 M SO solutions, either with or without an added nitrile compound or SnCl,. The solutions were saturated with CO by bubbling the gas through their storage reservoirs before admitting them into the sample cell. 

PM-IRRAS Polarization-modulated infrared reflertion absorption specTroscopy... 

Chronocoulometry and photon polarization modulation infrared reflec-tion/absorption spectroscopy have been employed [311] to study the fusion of dimyristoylphosphatidylcholine vesicles onto an Au(lll) electrode. The fusion was controlled either by the electrode potential, or charge. Film characteristics was also potential dependent. After removing the film from the electrode surface (negative potential), phospholipid molecules remained in its close proximity, in the ad-vesicle state. Several electrochemical and nonelec-trochemical methods have been applied [312, 313] to investigate the spreading of small unilamellar vesicles onto Au(lll) electrode. Vesicles fused onto the surface at > —0.5 V (versus SSCE), to form defected bilayers in contact with the metal surface. At more negative potentials, the film was removed from the electrode surface, but it still remained in its close proximity. 

Sum Frequency Generation and Polarization-Modulation Infrared Reflection Absorption Spectroscopy of Functioning Model Catalysts from Ultrahigh Vacuum to Ambient Pressure... 

Volume 50 of Advances in Catalysis, published in 2006, was the hrst of a set of three focused on physical characterization of solid catalysts in the functioning state. This volume is the second in the set. The hrst four chapters are devoted to vibrational spectroscopies, including Fourier transform infrared (Lamberti et al.), ultraviolet Raman (Stair), inelastic neutron scattering (Albers and Parker), and infrared-visible sum frequency generation and polarization-modulation infrared rehection absorption (Rupprechter). Additional chapters deal with electron paramagnetic resonance (EPR) (Bruckner) and Mossbauer spectroscopies (Millet) and oscillating microbalance catalytic reactors (Chen et al.). 

PMIRRAS polarization modulation infrared reflection-absorption spectroscopy... 

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. 

Ren Y., Hossain M.M., limura K.I. and Kato T., CH3(CH2)COOH/Cd system on the aqueous cadmium acetate solution investigated in situ by polarization modulation infrared spectroscopy, J. Pfys. Chem. BIOS (2001) pp. 7723-7729. 

Photoinduced birefringence illustrates what is happening in bulk, but use of time-dependent polarization modulation infrared spectroscopy can offer a detailed insight at the molecular level. Different infrared bands can be monitored in time, and the change in their orientation function allows one almost to watch the different groups move in real time. In order to do this, the process must be slowed down considerably, which is achieved by using a fraction of the pump intensity. 

Rupprechter G (2007) Sum frequency generation and polarization-modulation infrared reflection absorption spectroscopy of functioning model catalysts from ultrahigh vacuum to ambient pressure. Adv Catal 51 133... 

Ozensoy E, Meier D, Goodman D (2002) Polarization modulation infrared reflection absorption spectroscopy at elevated pressures CO adsorption on Pd(lll) at atmospheric pressures. J Phys Chem B 106 9367... 

A prerequisite for the development indicated above to occur, is a parallel development in instrumentation to facilitate both physical and chemical characterization. TEM and SPM based methods will continue to play a central role in this development, since they possess the required nanometer (and subnanometer) spatial resolution. Optical spectroscopy using reflection adsorption infrared spectroscopy (RAIRS), polarization modulation infrared adsorption reflection spectroscopy (PM-IRRAS), second harmonic generation (SFIG), sum frequency generation (SFG), various in situ X-ray absorption (XAFS) and X-ray diffraction spectroscopies (XRD), and maybe also surface enhanced Raman scattering (SERS), etc., will play an important role when characterizing adsorbates on catalyst surfaces under reaction conditions. Few other methods fulfill the requirements of being able to operate over a wide pressure gap (to several atmospheres) and to be nondestructive. 

Kocharova N, Leiro J, Lukkari J et al (2008) Self-assembled carbon nanotubes on gold polarization-modulated infrared reflection-absorption spectroscopy, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy study. Langmuir 24 3235-3243... 

During this work, we analyzed the organization, the morphology, and the preferential adsorption of these copolymers and how these properties would be influenced by the interfacial interactions that could be established between the polymer and the chemical functionalities grafted onto the adsorption substrate. Our results were mainly based on two surface techniques polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and atomic force microscopy (AFM). 

Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS)... 

Polarization-modulation infrared reflection-absorption spectroscopy (PM-IR-RAS) spectra were recorded with a Bruker ITS 66/S Fourier transform infrared spectrometer equipped with a PMA 37 polarization modulation module and a ititrogen-cooled MCT detector. The infrared beam was first p-polarized with a ZnSe wire grid polarizer (Specac) before passing through a photoelastic modulator (Hinds Instruments, PEM-90), which modulated at a frequency of 74 kHz. A lock-in ampHfier (Stanford model SR-830) was used to obtain the PM-IRRAS spectra. The half-wave retardation frequency was set at 4000 cm . The PM-IR-RAS spectra were recorded as S= R -Rs)/(R +Rg). A total of 250 scans at a resolution of 4 cm were collected for each measurement at an angle of incidence of 82.5° with respect to the normal to the sample surface. 

One of the most commonly applied IR techniques developed to overcome these problems is the external reflectance technique. In this method, the shong solvent absorption is minimized by simply pressing a reflective working electrode against the IR transparent window of the electrochemical cell. The sensitivity problem, that is, the enhancement of the signal/noise ratio in the case of external reflectance techniques is solved by various approaches. These are, for instance, electrochemically modulated infrared spectroscopy (EMIRS), in situ FTIR (which use potential modulation), and polarization modulation infrared reflection absorption spectroscopy (PM-IRAS, FTIR) [86,117-123]. 

Meier et al. [166] applied polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) to simultaneously monitor hquid phase and adsorbed species during benzyl alcohol selox over Pd(l 11). Anaerobic conditions favored CO surface accumulation via decarbonylation, while surface oxygen fadhtates CO oxidation, leaving no surface residues strongly adsorbed CO and oxygen poison the active surface sites. 

The second means of increasing the S/N ratio, which has also been employed with FTIR spectrometers, involves modulating the polarization state of the light, a technique termed polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). This technique relies on a subsidiary selection rule, valid... 

A second lock-in detection method that was employed is polarization modulation, which involves modulating the polarization state of the incident infrared beam, and is again an extension of an approach developed for the study of the gas-solid interface [80]. Polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) relies upon the principles underlying the surface selection rule... 

The complexation of PABA with nucleotides was further studied using polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS). PM-IRRAS spectra of PABA films exhibit all the characteristic vibrations of polyaniline and boronic acid (Figure 3.27) [93, 94]. After complexation with NAD+ (Figure 3.27, b) and NADH (Figure 3.27, c), the disappearance of the free B-OH group vibration at 986 cm and increase in the intensity of the asymmetric B-O bond vibration at 1330 cm indicate the formation of boronate ester. The new vibrations at 1080 and 1470 cm have been attributed to ribose and adenine moieties, respectively [153]. The vibrations at 1218 (NAD+), 1245... 

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