Lasers techniques, supersonic jets

Ishiuchi S, Yamada K, Chakraborty S, Yagi K, Fujii M (2013) Gas-phase spectroscopy and anharmonic vibrational analysis of the 3-residue peptide Z-Pro-Leu-Gly-NH2 by the laser desorption supersonic jet technique. Chem Phys 419 145... 

More commonly, the resonant two-photon process in Figure 9.50(c) is employed. This necessitates the use of two lasers, one at a fixed wavenumber Vj and the other at a wavenumber V2 which is tunable. The first photon takes the molecule, which, again, is usually in a supersonic jet, to the zero-point vibrational level of an excited electronic state M. The wavenumber of the second photon is tuned across the M to band system while, in principle, the photoelectrons with zero kinetic energy are detected. In practice, however, this technique cannot easily distinguish between electrons which have zero kinetic energy (zero velocity) and those having almost zero kinetic energy, say about 0.1 meV... 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

Other techniques that have been used to determine polycyclic aromatic hydrocarbons in soil extracts include ELISA field screening [86], micellar elec-tr okinetic capillary chromatography [ 87], supersonic jet laser-induced fluorescence [88,89], fluorescence quenching [90], thermal desorption gas chromatography-mass spectrometry [81,90,100], microwave-assisted extraction [91], thermal desorption [92], immunochemical methods [93,94], electrophoresis [96], thin layer chromatography [95], and pyrolysis gas chromatography [35]. 

A number of less commonly used analytical techniques are available for determining PAHs. These include synchronous luminescence spectroscopy (SLS), resonant (R)/nonresonant (NR)-synchronous scan luminescence (SSL) spectrometry, room temperature phosphorescence (RTP), ultraviolet-resonance Raman spectroscopy (UV-RRS), x-ray excited optical luminescence spectroscopy (XEOL), laser-induced molecular fluorescence (LIMP), supersonic jet/laser induced fluorescence (SSJ/LIF), low- temperature fluorescence spectroscopy (LTFS), high-resolution low-temperature spectrofluorometry, low-temperature molecular luminescence spectrometry (LT-MLS), and supersonic jet spectroscopy/capillary supercritical fluid chromatography (SJS/SFC) Asher 1984 Garrigues and Ewald 1987 Goates et al. 1989 Jones et al. 1988 Lai et al. 1990 Lamotte et al. 1985 Lin et al. 1991 Popl et al. 1975 Richardson and Ando 1977 Saber et al. 1991 Vo-Dinh et al. 1984 Vo- Dinh and Abbott 1984 Vo-Dinh 1981 Woo et al. 1980). More recent methods for the determination of PAHs in environmental samples include GC-MS with stable isotope dilution calibration (Bushby et al. 1993), capillary electrophoresis with UV-laser excited fluorescence detection (Nie et al. 1993), and laser desorption laser photoionization time-of-flight mass spectrometry of direct determination of PAH in solid waste matrices (Dale et al. 1993). 

The electronic spectra of rare gas dimers have been a subject of interest for many years, mainly because these dimers are model systems for studying van der Waals interactions, and because of their potential as media for VUV and XUV lasers. Yet very little is known about the excited states of these dimers. Two experimental techniques were combined in our laboratory for this investigation four-wave summixing (4-WSM) and a pulsed supersonic jet to produce rotationally and vibrationally cold dimer molecules. In this way it was possible to resolve rovibronic structures in several isotopic band systems of Xe2, Kr2 and Ar2, in the region 150 to 104 nm, to determine the relevant molecular constants, and to calculate potential energy curves for the ground states and the three lowest (stable) excited states, for all three dimers [41,42,43]. 

One example is intracavity Raman spectroscopy of molecules in a supersonic jet, demonstrated by van Helvoort et al. [8.36]. If the intracavity beam waist of an argon-ion laser is shifted to different locations of the molecular jet (Fig. 8.10), the vibrational and rotational temperatures of the molecules (Sect. 9.2) and their local variations can be derived from the Raman spectra. More details of recent techniques in linear laser Raman spectroscopy can be found in [8.11,8.37]. 

Nowadays, the combination of laser ablation with Fourier transform microwave spectroscopy techniques, in supersonic jets, has enabled the gas-phase study of such systems. In this chapter, these techniques, including broadband spectroscopy, as well as results of their application into the study of the conformational panorama and structure of biomolecular building blocks, such as amino acids, nucleic bases, and monosaccharides, are briefly discussed, and with them, the tools for conformational assignation - rotational constants, nuclear quadrupole coupling interaction, and dipole moment. 

The main objective of this chapter is to summarize the advances attained in the knowledge of the strucmre of isolated biomolecular building blocks by the combination of the experimental methods that combine laser ablation with Fourier transform microwave spectroscopy techniques in supersonic jets. 

During the last ten years, reactive collisions Rg +X2 or Rg+X2 leading to the RgX excimer through the harpoon mechanism have been widely studied [7]. These systems (mainly Xe+Cl2 or Br2> have been the first ones where the collision complex was excited in the gas phase by one photon [8] or two photon excitation [9]. Here the same two-photon excitation technique has been used for the excitation of the Xe-X2 Van der Waals complexes (X2 = Q2 B12, 12)- hi this experiment only one frequency doubled dye laser was used, ai visible light (from 5M to 500 nm) or the second hannonic or both were focused into the supersonic jet where the complexes are formed. The resulting fluorescence was detected with 10 nm resolution. Our results will then be compared with the coUisional ones. 

Since the 1980s, some conceptually new photoionization techniques have appeared in the field of gas-phase investigations whose resolution is better than that of the conventional UPS technique by some orders of magnitude. Two technical novelties preceded the appearance of these techniques the introduction of supersonic jets in photoelectron spectroscopy and the availability of high-energy lasers. 

Although there were some early attempts to analyze the vibrational fine structure contained in the near ultraviolet vapor phase spectrum of acetaldehyde, these studies were generally unsuccessful because of the diffuse and congested nature of the bands. It has only been in the last several years that the problem has been resolved by the powerful techniques of supersonic jet-laser excitation spectroscopy. 

Interaction of high-intensity laser pulse with supersonic gas-jets delivered by fast electromagnetic valves is the most common technique in LWF experiments worldwide. This kind of target allows a uniform, underdense plasma to be the interaction medium, with a density that can be tuned by managing... 

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