Supersonic jets, Fourier-transform

Fourier transform techniques have become very powerful, particularly when used with pulsed sources of the sample. They are ubiquitous in studies of van der Waals molecules, in which two or more entities are very weakly bound together in the gas phase, such as HCT Ar, but are also used to determine structures of many other compounds, of which the mixed alkali halide dimer LiNap2 is an example. In a typical experiment, the sample is introduced into the cell in a pulsed supersonic jet expansion, the rotational temperature being reduced to a few Kelvin. A pulse of microwave radiation then aligns the dipole moments of the molecules, so that the sample is polarized on a macroscopic scale. The subsequent decay of this polarization is recorded, and Fourier transformation of the free induction decay yields the spectrum [9]. 

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. 

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