Normal incidence monochromator

The features in C1-C4 normal alkanes discussed in Section 3 seem to be generalized to a wide range of molecules, and thus we conclude that the major part of the photoabsorption cross sections of molecules (cr) is associated with the ionization and excitation of the outer-valence electrons. Hence, there is a strong need to measure the absolute values of a in the vacuum ultraviolet range, particularly in the range of the incident photon energy 10-30 eV, which is covered by the normal incidence monochromator used to monochromatize synchrotron radiation. The photoionization (cr ) and photodissociation (cd) cross sections. 

We had previously used this technique for studying several alkali halides, including Nal, (23) the cesium halides (2A) and the rubidium halides. (25) The apparatus consisted of a one-meter normal incidence monochromator and a magnetic mass spectrometer. In these earlier studies, ionic species attributable to dimer and monomer were studied, but the intensity of trimer was too weak for measurement. With our more recent interest in trimer, we once again turned to the lithium halides. This time, our apparatus consisted of a three-meter normal incidence monochromator and a quadrupole mass spectrometer. (7 )... 

Fig. 2.3 Geometrical arrangement of a normal incidence monochromator. The important directions of the experiment are additionally shown...

Due to the structurally anisotropic nature of the aligned polymers, samples are mounted on a rotation stage between the focusing lens and the entrance slits of the monochromator. The sample film is rotated from 0 to 90° with respect to normal incidence for the laser beam. The SHG signal is measured in transmission. 

The normal-incidence values plotted in Figure 2-11 may be used as a first approximation for prisms, for which the angle of incidence necessarily differs from 0°. Taking into account the fact that in most prism monochromators the beam is reflected back through the prism... 

The reflectance and PR measurements of samples I-II and samples IV-VI, respectively, were carried out at near normal incidence between 6 and 10 K and at 295 K. For the PR measurements, the pump beam at 300 nm (4.13 eV) was obtained from a combination ofa 150 W Xe lamp with a 1-m monochromator, while the beam for both the reflectance and PR probe was derived by dispersing the light from a 75 W Xe lamp with a 0.64-m monochromator and polarizing it with a Glan-Taylor prism. The reflected light was detected by a silicon photodiode using standard lock-in techniques. 

The continuous-wave (cw) PL spectra of the M-plane GaN films (samples VII and V111) were excited at 244 nm by a frequency-doubled Ar+ laser, dispersed by a 1-m monochromator, and detected by a UV-enhanced GaAs photomultiplier. The polarization properties of the PL spectra were studied by polarizing the emitted PL signal before it entered the monochromator. All spectra were recorded under normal incidence so that the c axis of the GaN films was oriented perpendicular to the propagation direction of the incoming light. Excitation power densities of up to 50 W cm were used. 

Laue Method for Macromolecule X-Ray Diffraction. As indicated above it is possible to determine the stmctures of macromolecules from x-ray diffraction however, it normally takes a relatively long period of data collection time (even at synchrotrons) to collect all of the data. A new technique, the Laue method, can be used to collect all of the data in a fraction of a second. Instead of using monochromated x-rays, a wide spectmm of incident x-rays is used. In this case, all of the reflections that ate diffracted on to an area detector are recorded at just one setting of the detector and the crystal. By collecting many complete data sets over a short period of time, the Laue method can be used to foUow the reaction of an enzyme with its substrate. This technique caimot be used with conventional x-ray sources. 

HREELS experiments [66] were performed in a UHV chamber. The chamber was pre-evacuated by polyphenylether-oil diffusion pump the base pressure reached 2 x 10 Torr. The HREELS spectrometer consisted of a double-pass electrostatic cylindrical-deflector-type monochromator and the same type of analyzer. The energy resolution of the spectrometer is 4-6 meV (32-48 cm ). A sample was transferred from the ICP growth chamber to the HREELS chamber in the atmosphere. It was clipped by a small tantalum plate, which was suspended by tantalum wires. The sample was radia-tively heated in vacuum by a tungsten filament placed at the rear. The sample temperature was measured by an infrared (A = 2.0 yum) optical pyrometer. All HREELS measurements were taken at room temperature. The electron incident and detection angles were each 72° to the surface normal. The primary electron energy was 15 eV. 

The Compton profile measurements on Cu and Cu 953AI0047 were performed at ID 15b of the ESRF. Figure 1 shows the setup of the scanning-type Compton spectrometer used. It consists of a Si (311) monochromator (M), a Ge (440) analyzer (A) and a Nal detector (D). The signal of an additional Ge solid state detector (SSD) was used for normalization. ES, CS and DS denote the entrance slit, the collimator slit and the detector slit, respectively. For each sample 10 different directions were measured with approximately 1.5-2 x 103 7 total counts per direction. The incident energy was 57.68 keV for the Cu and 55.95 keV for the Cuo.953Alo.047 measurement. 

Figure B3.6.5 The inner filter effect. A cuvette (10 x 10-mm) is represented in plan view, with the collimated incident beam from the monochromator having intensity /0. As a result of absorption by the protein solution, the intensity of the beam through the cuvette will decrease steadily, emerging with intensity /. The values are illustrated for a solution having an absorbance at the excitation wavelength of 0.1. The optics of the fluorescence detector are focused so that only fluorescence originating from the volume depicted by the heavily shaded square is seen by the photomultiplier. Thus the observed normalized fluorescence intensity will be less than that expected from the protein at infinite dilution. The fluorescence passes through the protein solution on its way to the detector and will be further decreased in intensity if the solution absorbs at the wavelengths of the emitted radiation.

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