Time-resolved laser spectrometry

Figure 7. Time-resolved mass spectrometry. AU-trcms-(2, 4, 6, 8) decatetraene was excited to its 5 2 electronic origin with a femtosecond pulse at A-pump — 287 nm. The excited-state evolution was probed via single-photon ionization using a femtosecond pulse at ApIObe = 235 nm. The time resolution in these experiments was 290 fs (0.3 ps). The parent ion CioH signal rises with the pump laser, but then seems to stay almost constant with time. The modest decay observed can be fit with a single exponential time constant of 1 ps. Note that this result is in apparent disagreement with the same experiment performed at Xprobe — 352 nm, which yields a lifetime of 0.4 ps for the S2 state. The disagreement between these two results can be only reconciled by analyzing the time-resolved photoelectron spectrum.

CLM method can also be combined with various kinds of spectroscopic methods. Fluorescence lifetime of an interfacially adsorbed zinc-tetra-phenylporphyrin complex was observed by a nanosecond time-resolved laser induced fluorescence method [25]. Microscopic resonance Raman spectrometry was also combined with the CLM. This combination was highly advantageous to measure the concentration profile at the interface and a bulk phase [14]. Furthermore, circular dichroic spectra of the liquid-liquid interface in the CLM could be measured [19]. 

The overall diagram of evolution of the excited states and reactive intermediates of a photoinitiating system working through its triplet state can be depicted in Scheme 10.2 [249]. Various time resolved laser techniques (absorption spectroscopy in the nanosecond and picosecond timescales), photothermal methods (thermal lens spectrometry and laser-induced photocalorimetry), photoconductivity, laser-induced step scan FTIR vibrational spectroscopy, CIDEP-ESR and CIDNP-NMR) as well as quantum mechanical calculations (performed at high level of theory) provide unique kinetic and thermodynamical data on the processes that govern the overall efficiency of PIS. 

Bystol, A. J., Whitcomb, J. L., and Campiglia, A. D., Solid-liquid extraction laser excited time-resolved ShpoTskii spectrometry a facile method for the direct detection of 15 priority pollutants in water samples. Environ. Sci. Technol., 35, 2566-2571, 2001. 

Vapour-phase Species. The chemical properties of carbon vapour have been reviewed by Skell et al The report describes the preparation of and compositions of the vapour and discusses the chemistry of the constituent species, particularly C, Cg, C3, and C4. Several papers describing detailed aspects of the chemistry of these vapour-phase species have also been published. Chemical reactions of C, Cg, and C3, formed by laser-induced vaporization of either graphite or tantalum carbide, with oxygen, hydrogen, or methane have been studied by means of time-resolved mass spectrometry and gas-phase titrations in an attempt to determine the relative abundances of these three species in the vapour phase (Table 1). The techniques developed and... 

During the last two decades, there has been an enormous increase in the use of photophysical methods in supra-molecular chemistry. Until recently, photophysical methods, such as transient spectrometry and time-resolved fluorescence spectrometry, were primarily research tools in the arenas of photokinetics of small molecules, materials physics, and biophysics. This situation changed dramatically with the introduction of commercial, user-friendly electro-optical components such as charge-coupled detector (ED)-based spectrometers, solid-state pulsed lasers, and other instrumentation necessary for time-resolved measurements. As a result, time-resolved spectrometry became more available to the community of supramolecular chemists, who now reached the level of sophistication that can benefit from the new horizons offered. 

Van Breemen, R.B., Snow, M., Cotter, R.J. (1983) Time-resolved Laser Desorption Mass Spectrometry. 1. Desorption of Preformed Ions. Int. J. Mass Spectrom. Ion Phys. 

Experimental design of time-resolved mass spectrometry (TRMS) systems can greatly affect temporal resolution in the analysis of dynamic samples (see also Section 4.2). The two popular MS approaches - laser desorption/ionization (LDI)-MS and electrospray ionization (ESI)-MS - are suitable for studies of enzymatic reactions [8]. 

TRLFS Time-resolved laser-induced fluorescence spectrometry (analyti-... 

Conventional optical absorption spectrometry has detection limits of between 0.01 and 1 mM for the actinides. Highly sensitive spectroscopic methods have been developed, based on powerful laser light sources. Time resolved laser fluorescence spectroscopy (TRLFS), based on the combined measurement of relaxation time and fluorescence wavelength, is capable of speciating Cm(III) down to 10 mol/L but is restricted to fluorescent species like U(VI) and Cm(III). Spectroscopic methods based on the detection of nonradiative relaxation are the laser-induced photoacoustic spectroscopy (LPAS) and the laser-induced thermal leasing spectroscopy (LTLS). Like conventional absorption spectroscopic methods, these newly developed methods are capable of characterizing oxidation and complexation states of actinide ions but with higher sensitivity. 

Radziemski L, Loree T, Cremes D, Hoffman N (1983) Time resolved laser induced breakdown spectrometry of aerosols. Anal Chem 55 1246—1253 Reiche I, Vignand C, Champagnon B et al (2001) From mastodon ivory to gemstone The origin of turquoise color in odontolite. Am Miner 86 1519—1524... 

L.J. Radziemski, T.R. Loree, D.A. Cremers, N.M. Hoffman Time-resolved laser-induced breakdown spectrometry of aerosols. Anal. Chem. 55, 1246 (1983) J.A. Millard, R.H. Dalling, L.J. Radziemski Time-resolved laser-induced breakdown spectrometry for the rapid determination of beryllium in beryllium-copper alloys. Appl. Spectr. 40, 491 (1986)... 

The cis-trans isomerisation of retinal is concerned also in photochemical change in some bacteria where the membrane chromatophore is the protein bacteriorhodopsin. The chain of reactions following absorption of a photon has been studied by time-resolved laser flash spectrometry. The overall reaction has a half-life of about 10 ms, but there are several intermediate reactions with rise times of femtoseconds to milliseconds. In one of these a proton is transferred across bacteriorhodopsin this leads to an electrochemical proton-concentration gradient across the membrane, which is used by the bacterium as a driving force for ATP synthesis [57]. Since the structure of bacteriorhodopsin is known, it is a useful system for the study of membrane transport. 

L.J. Radziemski, T.R. Loree, D.A. Cremers, N.M. Hoffman Time-resolved laser-induced breakdown spectrometry, of aerosols. Anal. Chem. 55, 1246 (1983)... 

In this book, most chapters deal with FT-IR spectrometry and its applications to various methods of infrared spectroscopic measurements. Only terahertz spectrometry in Chapter 19 and a large part of time-resolved infrared spectrometry in Chapter 20 are laser-based measurements. This shows how widely FT spectrometry is used at present in the measurements of vibrational spectfa. 

The application of semiconductor lasers to a broad range of areas in spectrometry has recently been reviewed by Imasaka. 67, 68) Topics covered include photoacoustic, absorption, and thermal lens, as well as steady-state and time-resolved fluorescence. Patonay et al. have reviewed the application of diode lasers to analytical chemistry.(69) The performance of several commercially available laser diodes for fluorimetry has recently been compared. 70 ... 

Laser-flash photolysis of (203) in solution affords the ketene (204) and this is the first time that this ketene has been observed using time-resolved IR spectroscopy, Although other workers have previously reported the formation of this species. The present work reports the kinetics of the reaction of the ketene with water, methanol and diethylamine. The products obtained from the irradiation of a series of AT-acetoacetyl-a-amino acids have been identified by gas chromatography and chemical ionization mass spectrometry. ... 

In their recent landmark femtosecond-resolved mass spectrometry studies, Zewail and coworkers have used mass spectrometry for monitoring the time-resolved unimolecular fragmentation of neutral norbomene and norbomadiene. In both cases, the RDA reactions occurred, but only in the norbomadiene case was the well-known H loss giving rise to C7H7+ ions found to compete. Still, non-concertedness and biradicaloid character of the intermediates is being addressed by femtosecond dynamic studies. In this context, Kompa and coworkers" have compared the expulsion of H+ from femtosecond-laser-irradiated... 

Hirata T (2002) In-situ precise isotopic analysis of tungsten using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) with time resolved data acquisition. J Anal Atom Spectrom 17 204-210. 

Figure 4.2. Experimental set-up for kinetic studies of SiHj reactions by excimer laser photolysis in a tubular slow-flow reactor with time-resolved detection by molecular beam sampling, near-threshold ionization electron impact mass spectrometry...

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