Nanosecond spectrometer

Cu-loaded zeolites were prepared by the ion exchange from Cu salt solutions, their chemical composition is given in the Figures. The conditions of reduction of the Cu zeolites were chosen to obtain a maximum reduction of the Cu ions to Cu (see further and Refs. 6 and 9). Luminescence spectra in the range of 350-750 nm were recorded at 298 K employing laser kinetic nanosecond spectrometer (Applied Photophysics) equipped with a Xe Cl excimer laser ... 

An Applied Photophysics Model SP 2X nanosecond spectrometer incorporating an alternating polarization rotation unit ( ) was used for the time-resolved fluorescence anisotropy measurements. An excitation wavelength of 365 nm was employed for excitation of the anthracene end-groups and emission above 400 nm was isolated with a Schott GG 400 filter. 

This research was supported by the National Institutes of Health (GM26133). The author acknowledges the contribution of Timothy Kohl for the development of the data analysis routines for the nanosecond spectrometer and the continued dialog and collaboration of John Golbeck in this laboratory s investigations in Photosystem 1. 

The design of a pulsed EPR spectrometer depends heavily on tlie required pulse lengdi and pulse power which in turn are mainly dictated by the relaxation times of tlie paramagnetic species to be studied, but also by the type of experiment perfomied. When pulses of the order of a few nanoseconds are required (either to compete... 

Yuzawa T, Kate C, George M W and Hamaguchi H O 1994 Nanosecond time-resolved infrared spectroscopy with a dispersive scanning spectrometer Appl. Spectrosc. 48 684-90... 

A laser pulse strikes the surface of a sample (a), depositing energy, which leads to melting and vaporization of neutral molecules and ions from a small, confined area (b). A few nanoseconds after the pulse, the vaporized material is either pumped away or, if it is ionic, it is drawn into the analyzer of a mass spectrometer (c). 

There are two common occasions when rapid measurement is preferable. The first is with ionization sources using laser desorption or radionuclides. A pulse of ions is produced in a very short interval of time, often of the order of a few nanoseconds. If the mass spectrometer takes 1 sec to attempt to scan the range of ions produced, then clearly there will be no ions left by the time the scan has completed more than a few nanoseconds (ion traps excluded). If a point ion detector were to be used for this type of pulsed ionization, then after the beginning of the scan no more ions would reach the collector because there would not be any left The array collector overcomes this difficulty by detecting the ions produced all at the same instant. 

As the laser pulse is in the nanosecond range, a fast mass spectrometer has to be coupled in series. In most cases, MALDI is coimected to a time-of-flight (TOF) mass spectrometer with which m/z ratios are determined by precisely measuring the time an ion needs to pass from the ion source to the detector. Besides its abil-... 

Fig. 8.2 Principle of the MALDI process. Initially, analyte and matrix are co-crystal I ized. After evaporation of the solvent, a nanosecond laser pulse is directed onto the crystalline surface, and both matrix and analyte molecules are desorbed. A complex reaction cascade leads to the formation of charged analyte molecules that reach the mass spectrometer without significant fragmentation.

The outlook is good for applications of these picosecond methods to an increasing number of studies on reactive intermediates because of the limitations imposed by the time resolution of nanosecond methods and the generally greater challenges of the use of a femtosecond spectrometer. The pump-probe technique will be augmented in more widespread applications of the preparation-pump-probe method that permits the photophysics and photochemistry of reactive intermediates to be studied. 

The prompt appearance of these absorption bands within a nanosecond response time of the kinetic spectrometer (Fig. la,b) is a direct indication that intense 308-nm laser pulses induce photoionization of 2AP [10] ... 

Cu+ emission spectra were recorded using a nanosecond laser kinetic spectrometer (Applied Photophysics). Cu+-zeolites were excited by the laser beam of the XeCl excimer laser (Lambda Physik 205, emission wavelength 308 nm, pulse width 28 ns, pulse energy 100 mJ). The 320-nm filter was situated between 2 mm thick silica cell and monochromator. Emission signal was detected with the photomultiplier R 928 (Hamamatsu), recorded with the PM 3325 oscilloscope and processed by a computer. All the luminescence measurements were carried out at room temperature. The Cu+ emission spectra were constructed from the values of luminescence intensity at the individual wavelengths of emission in selected times after excitation (2, 5,10, 20, 50, 100 and 200 ps). For details see Ref [7]. 

Perhaps the greatest attribute that TOF-MS may apply to elemental mass spectrometry is the ability to provide simultaneous multielemental analysis. Of course, a TOF-MS does not record all the masses in the spectrum simultaneously the time difference between adjacent masses is typically in the nanosecond regime. However, all masses are sampled into the mass spectrometer simultaneously and an entire spectrum is generated from each injected ion pulse. Because successively recorded mass spectra are obtainable in short periods in a TOF-MS, especially in instances in which there is a small, well-defined mass range of interest, thousands of mass spectra can be obtained each second. 

The lifetime of a particle in the mass spectrometer is about 20 ns (nanosecond = 10 9 second) so benzyne can exist for at least that long in the gas phase. 

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