Supersonic jet spectroscopy

Nesbitt D J 1994 High-resolution direct infrared laser absorption spectroscopy in slit supersonic jets intermolecular forces and unimolecular vibrational dynamics in clusters Ann. Rev. Phys. Chem. 45 367-99... 

Raman scattering is normally of such very low intensity that gas phase Raman spectroscopy is one of the more difficult techniques. This is particularly the case for vibration-rotation Raman spectroscopy since scattering involving vibrational transitions is much weaker than that involving rotational transitions, which were described in Sections 5.3.3 and 5.3.5. For this reason we shall consider here only the more easily studied infrared vibration-rotation spectroscopy which must also be investigated in the gas phase (or in a supersonic jet, see Section 9.3.8). 

Spectroscopy of molecules in supersonic jets 9.3.11.1 Properties of a supersonic Jet... 

Laser spectroscopy is such a wide subject, with many ingenious experiments using one or two CW or pulsed lasers to study atomic or molecular stmcture or dynamics, that it is difficult to do justice to it at the level at which Modern Spectroscopy is aimed. In this edition 1 have expanded the section on supersonic jet spectroscopy, which is an extremely important and wide-ranging field. 

New IR techniques introduced for the study of prototropic tautomerism include IR dicroism for the photoinduced double proton transfer in por-phine 71 (Scheme 24) [89CPH(136)165], and IR spectroscopy in a supersonic jet (less than 50 K) for demonstrating the presence, in these conditions, of 2//-benzotriazole (57b) [96CPL(262)689]. 

If two different three-dimensional arrangements in space of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are called conformationsIf they are not interconvertible, they are called configurations Configurations represent isomers that can be separated, as previously discussed in this chapter. Conformations represent conformers, which are rapidly interconvertible and are thus nonseparable. The terms conformational isomer and rotamer are sometimes used instead of conformer . A number of methods have been used to determine conformations. These include X-ray and electron diffraction, IR, Raman, UV, NMR, and microwave spectra, photoelectron spectroscopy, supersonic molecular jet spectroscopy, and optical rotatory dispersion (ORD) and CD measurements. Some of these methods are useful only for solids. It must be kept in mind that the conformation of a molecule in the solid state is not necessarily the same as in solution. Conformations can be calculated by a method called molecular mechanics (p. 178). 

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... 

Piuzzi F, Mons M, Dimicoli I, Tardivel B, Zhao Q (2001) Ultraviolet spectroscopy and tautomerism of the DNA base quanine and its hydrate formed in a supersonic jet. Chem Phys 270 205... 

Although the spectroscopy of free radicals and their photochemistry are intimately related, this review does not specifically address the spectroscopy of free radicals. Several comprehensive reviews on spectroscopy of free radicals in supersonic jets have been made available recently,2-5 and more information can be obtained from these articles. 

M. Quack, U. Schmitt, and M. A. Suhm, FTIR spectroscopy of hydrogen fluoride clusters in synchronously pulsed supersonic jets Isotopic isolation, substitution and 3 D condensation. Chem. Phys. Lett. 269, 29 38 (1997). 

N. Guchhait, T. Ebata, and N. Mikami, Discrimination of rotamers of aryl alcohol homologues by infrared ultraviolet double resonance spectroscopy in a supersonic jet. J. Am. Chem. Soc. 121, 5705 5711 (1999). 

Although this book is devoted to molecular fluorescence in condensed phases, it is worth mentioning the relevance of fluorescence spectroscopy in supersonic jets (Ito et al., 1988). A gas expanded through an orifice from a high-pressure region into a vacuum is cooled by the well-known Joule-Thomson effect. During expansion, collisions between the gas molecules lead to a dramatic decrease in their translational velocities. Translational temperatures of 1 K or less can be attained in this way. The supersonic jet technique is an alternative low-temperature approach to the solid-phase methods described in Section 3.5.2 all of them have a common aim of improving the spectral resolution. 

Ito M., Ebata T. and Mikami N. (1988) Laser Spectroscopy of Large Polyatomic Molecules in Supersonic Jets, Ann. Rev. Phys. Chem. 

In this chapter, we give a brief overview of several novel features of excited-state proton transfer in chromophore-solvent clusters which have been revealed by the interplay of computational chemistry and spectroscopy in supersonic jets. In the future, concerted efforts of theory and spectroscopy will be necessary to investigate the evolution of these phenomena with increasing cluster size towards liquid-phase photochemistry. 

Since the turn of the present century, a series of linear complexes with the general formula NgMX (Ng = Ar, Kr, Xe M = Cu, Ag, Au X = F, Cl, Br) have been prepared and characterized by physical methods. These complexes were prepared by laser ablation of the metal from its solid and letting the resulting plasma react with the appropriate precursor. The complexes formed were then stabilized in a supersonic jet of argon gas. Characterization of these complexes was carried out mainly by microwave spectroscopy. 

The combination of supersonic-jet-laser spectroscopy and high-level ab initio calculations provides a powerful method for probing the geometrical structure and photophysical properties of small molecules. In this chapter, we described the experimental and theoretical characterizations of geometrical structures and elementary photoprocesses in supersonic free jet. The major focus of the review was on the OODR spectroscopy, which is designed to identify and characterize dark electronic states of the molecule. The main conclusions that emerge from the review can be summarized as follows. 

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