Tuning the monochromator

Spectral interferences are due to substances in the flame that absorb the same wavelength as the analyte, causing the absorbance measurement to be high. The interfering substance is rarely an element, however, because it is rare for another element to have a spectral line at exactly the same wavelength, or near the same wavelength, as the primary line of the analyte. However, if such an interference is suspected, the analyst can tune the monochromator to a secondary line of the analyte to solve the problem. 

Tuning the monochromator for variable wavelength anomalous dispersion experiments... 

Table 5.62 Usts the main characteristics of NEXAFS microscopy. Images are obtained by ras-tering the sample across the X-ray focus, while keeping the high-resolution monochromator fixed. Keeping the sample stationary and tuning the monochromator across the spectral range allows obtaining NEXAFS spectra with a spectral resolution typically of about 0.1 to 0.3 eV. NEXAFS microscopy...

Turn the monochromator wavelength setting to 285 nm using the coarse adjustment, then use the fine wavelength control to tune in to the line maximum at 285.2 nm. 

The spectral resolution can be measured directly from a spectrum. It depends on the emission peak width AA, at half height, measured in spectral units. Its value depends on the monochromator and its tuning. R defines the resolving power of a spectrometer that is, its ability to separate two lines of very close wavelength ... 

Following the heat-load monochromator, the X-ray bandwidth is narrowed to approximately 1 eV and centered on the nuclear resonance energy (14.4 kev for Fe). The high-resolution monochromator further reduces the X-ray bandwidth to about 1 meV and motorized scanning of this monochromator tunes the energy over a range (typically within 100 meV of the resonance) adequate to explore excitation or annihilation of vibrational quanta. The X-ray flux at the sample is about 10 photons/s ( 10 tW), which is very low compared to typical milliwatt beam powers in laser-based Raman experiments see Vibrational Spectroscopy). Additional X-ray optics may reduce the beam size. The cross section of the beam at the sample point is currently about 0.5 x 0.5 mm at station D of beam line 3ID at APS. 

An electric beam chopper and a tuned amplifier are incorporated into most AA instrument. Operationally, the power to the hoUow-cathode lamp is pulsed so that the light is emitted by the lamp at a certain number of pulses per second. On the other hand, aU of the light coming from the flame is continuous. When light leaves the flame, it is composed of pulsed, unabsorbed light from the lamp and a small amount of unpulsed flame spectrum and sample emission. The detector senses all light, but the amplifier is electrically tuned to accept only pulsed signals. In this way, the electronics in conjunction with the monochromator discriminate between the flame spectrum and sample emission. 

Methyl salicylate was placed in a rare gas matrix at 4.2 K. A tuneable dye laser was used to excite the sample, while a monochromator was used to measure the emission spectrum. By tuning the dye laser it was possible to measure the excitation as well as the fluorescence spectrum of methyl salicylate. A partially resolved vibrational progression was observed both in the emission and in the excitation spectra. A fluorescence lifetime of 12 ns was measured at all of the emission wavelengths. As expected deutera-tion changed the vibrational progressions. It also lengthened the fluorescence lifetime. From the vibronic structure it was argued that a double minimum potential does not exist in the excited states. An estimate of... 

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