Radiation, adsorption intensity

The adsorption maximum at 270 nm, as an indicator of the Ce " /Ce " transition, increases with increasing intensity of the 308 nm laser. Figure 9.58 also shows the difference of the optical densities as function of the wavelength of FS21 after exposure by a mask aligner, which emits a broad band radiation. The intensity in the 308 nm range corresponds to an energy density of 2 J cm of the excimer laser. 

The most widely used experimental method for determining surface excess quantities at the liquid-vapor interface makes use of radioactive tracers. The solute to be studied is labeled with a radioisotope that emits weak beta radiation, such as H, C, or One places a detector close to the surface of the solution and measures the intensity of beta radiation. Since the penetration range of such beta emitters is small (a ut 30 mg/cm for C, with most of the adsorption occurring in the first two-tenths of the range), the measured radioactivity corresponds to the surface region plus only a thin layer of solution (about 0.06 mm for C and even less for H). 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

A much thinner piece (0.4 mm.) of porous glass was used, and a simple adsorption system with a fused silica cell was constructed (152). The adsorption isotherm could be obtained at the same time that the sample was in the light beam of the spectrometer. This obviates the necessity of measuring the temperature of the sample with the intensities of radiation normally used in infrared spectrometers this effect can be quite significant, since most adsorbents are bad conductors of heat. 

Changes in intensity of semiconductor PL or EL can be used to detect molecular adsorption onto semiconductor surfaces [1,3]. PL occurs most efficiently when ultra-band-gap radiation excites electrons from the valence band to the conduction band of a direct-band-gap semiconductor and the electrons recombine radiatively with the holes left behind in the valence band. 

ATR studies of the biocorrosion of submerged copper surfaces have been reported. The IRE of a cylindrical internal reflectance cell (CIRCLE) was coated with a thin copper layer via a vacuum deposition technique (105). The copper layer reduces the sampling depth of the radiation outward from the surface of the IRE. Therefore, the intensity of the water bending band will vary with copper layer thicknesses of 4.1 nm or less. The copper layers were shown to be stable to exposure to water alone, but the presence of acidic polysaccahrides in the water caused a reduction in the copper layer thicknesses (106.107). The adsorption of a model compound, Gum Arabic, onto the coated IRE was detected by increases in the C-O stretching band of the pyranose units near 1050 cm"1 (106). 

The azimuthal dependence of the intensity of Vasym(C-O) in the P-polarised radiation shows a maximum at 9=90° indicating an alignment of the Rh(CO)2 in the <110> direction. Since the S and Pt fields are orthogonal, using S-polarised radiation at 9 = 0° Vasym(C-O) is not observed, but is observed at 9 = 90°. The two most likely adsorption geometries of the adsorbed gem-dicarbonyl are shown in Fig. 11, both with the C-0 bonds in a plane aligned in the <110> direction. 

Color." The most obvious effect produced in silica gel by radiation is a grayish-purple color (64), which can be almost surely attributed to the same type of center as that responsible for the similar color in irradiated quartz, namely, a positive hole trapped at an oxygen ion adjacent to a substitutional Al + impurity ion (65-67). The attribution rests on the similarity in optical absorption between irradiated gel and irradiated quartz (66), on the dependence of the intensity of the color on the aluminum content (69), and on the observation of a hyperfine interaction characteristic of the spin of the 2 a1 nucleus (I = 5/2) in the ESR spectrum of the irradiated gel (70). Furthermore, the ESR sextet and the color are annealed at comparable rates above 200° (70) and are both destroyed by adsorption of H2 at room temperature (64, 70). Their intensities increase in parallel as the aluminum content, the severity of preirradiation heat treatment, or the length of irradiation is increased (70). The concentration of the center does not increase indefinitely. After some lO i ev/gm, it approaches a limiting value which depends on the impurity content, for typical gels around lO H2/gm (69). 

Results contrasting markedly with the foregoing and showing net radiation-induced desorption rather than adsorption, have been obtained not only in containment vessels subject to intense beams of ionising radiations [ 1 ], but also with well-characterised single-crystal surfaces exposed to the radiations employed in modern surface spectroscopic techniques (cf. Table 1). The phenomenon of radiation-induced desorption from the walls of containment vessels has acquired new technological interest from the probability that plasma-induced desorption from the... 

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