Laser kinetic spectrometer

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]. 

Four different laboratories have built IR kinetic spectrometers for use with organometallic compounds. A fundamental feature of all these spectrometers is that the detector is AC coupled. This means that the spectrometers only measure changes in IR absorption. Thus, in the time-resolved IR spectrum, bands due to parent compounds destroyed by the flash appear as negative absorptions, bands due to photoproducts appear as positive absorptions, and static IR absorptions, due to solvents, for example, do not register at all. The important features of these spectrometers are listed in Fig. 2. Since three spectrometers have a line-tunable CO laser as the monochromatic light source, we begin with the CO laser. Then we look in more detail at spectrometers designed for gas phase and solution experiments. 

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] ... 

In a similar way, anthracene triplet (4>,gj3=0.71, z =6A,700Mr cmr ) and the naphthalene triplet (4>jg = 0.75, e j = 24,500 M" cm" ) in cyclohexane solution have been introduced as transient chemical actinometers for the third-harmonic (355 run) and fourth-harmonic (266 nm) output of Nd YAG lasers, respectively (44). In summary, transient chemical actinometers are ideal for accurately measuring the energy of single laser pulses, provided the quantum yields and extinction coefficients of the transients are well known (45 7). Thus, the well-established benzophenone actinometer (42-44) has been used as a reliable reference to calibrate the azobenzene actinometer (see section "Laser Intensity Measurements with the Azobenzene Actinometer" Doherty S, Hubig SM, unpublished results) and the Aberchrome 540 actinometer (48,49) for intensity measurements with pulsed Nd YAG and/or XeCl excimer lasers. However, such actinometer can only be used when a complete set of laser flash photolysis equipment including a kinetic spectrometer is available. 

Figure 2. Schematic layout of a typical suprananosccond kinetic spectrometer Q Q-switched laser with harmonic generators L lens X cw monitoring lamp S shutter A aperture (see Figure 3 for detail) C sample cuvette M monochromator PM, PD photodetectors O digital oscilloscope PC personal computer.

A suprananosecond kinetic spectrometer is schematically shown in Figure 2. The excitation source is a Q-switched Nd YAG laser (Continuum Surelite 1) which is capable of a iO-Hz repetition rate but is typically used in the replicate-one-shot mode. The nominal 6-ns pulse can contain up to 450 mJ at 1064 nm, which decreases after harmonic conversions to 532 nm, 355 nm, or 266 nm. In addition to these harmonic lines, the 355-nm line can be used to pump an OPO (Opotek Magieprism), which provides tunable radiation in the range 420 nm to ca. 900 nm. The selected photolysis beam is incident on one face of a 10 mm x 10 mm quartz cuvette containing the sample. 

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 ... 

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and a-nalysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral o-verlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluoro-hydroquinone and p-methoxyphenol is briefly discussed. 

To operate the ion TOF spectrometer in the velocity mode, we adapted a single-stage TOF spectrometer as shown in Fig. 3, which consisted of a repeller, an extractor (and guard rings, not shown) and a free-drift tube. After laser ionization, ions are extracted towards the MCP detector. For an ion with an initial kinetic energy Do, the total flight time t can be written as... 

Recent developments in laser technology and fast detection methods now allow the kinetic behaviour of the excited state species arising from absorption of radiation by polymers to be studied on time-scales down to the picosecond region ( ). An example of a time-resolved fluorescence spectrometer which can be used to study such ultrafast phenomena is illustrated in Figure 5 Q). 

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

In secondary-ion mass spectrometery (SIMS) and its sister technique fast atom bombardment mass spectrometry (FARMS), a surface is bombarded with energetic particles, and the kinetic energy of the particles converts substrate and chemisorbed atoms and molecules to gas-phase species. The ejected (or sputtered) material is subsequently interrogated using various analytical tools, such as lasers and mass spectrometers, to indirectly deduce information about the initial surface. The relationships between sputtered material and the surface, however, are not always clear, and erroneous conclusions are easily made. Computer simulations have demonstrated that a fundamental understanding of the sputtering process is required to interpret experimental data fully ... 

TRPES has been recently reviewed and details of the experimental method and its interpretation can be found elsewhere [5], Trans-azobenzene was introduced via a helium supersonic molecular beam into the interaction region of a magnetic bottle photoelectron spectrometer. The molecules were photoexcited by a tunable femtosecond laser pulse (pump pulse) with a wavelength of 280-350nm. After a variable time delay, the excited molecules were ionized by a second femtosecond laser pulse (probe pulse) with a wavelength of 200 or 207nm. The emitted photoelectrons were collected as a function of pump-probe time delay and electron kinetic energy. 

Clusters, produced in a supersonic expansion, are ionized by laser. Delayed pulsed extraction is used to send the ions towards a lm time-of-flight mass spectrometer perpendicular to the jet axis. During the delay time between ionization and extraction, the ions spot size increases, due to their kinetic energy. The result is a broader mass peak with a width that is related to the kinetic energy released after the ionization and can be deduced after calibration of the experiment. 

In the first experiment We used a reflectron type spectrometer to measure the kinetic energy distribution of electrons emitted by the interaction of an intense femtosecond laser with large Xe clusters [10]. 

The analytically important features of Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometry (1) have recently been reviewed (2-9) ultrahigh mass resolution (>1,000,000 at m/z. < 200) with accurate mass measurement even 1n gas chromatography/mass spectrometry experiments sensitive detection of low-volatility samples due to 1,000-fold lower source pressure than in other mass spectrometers versatile Ion sources (electron impact (El), self-chemical ionization (self-Cl), laser desorption (LD), secondary ionization (e.g., Cs+-bombardment), fast atom bombardment (FAB), and plasma desorption (e.g., 252cf fission) trapped-ion capability for study of ion-molecule reaction connectivities, kinetics, equilibria, and energetics and mass spectrometry/mass spectrometry (MS/MS) with a single mass analyzer and dual collision chamber. 

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