Laser-ablation molecular-beam Fourier transform microwave spectroscopy

In 2008, Alonso and coworkers reported a combined experimental and computational study of the conformations of cysteine. They located 11 low lying conformers at MP4/6-311-i i-G(d,p)//MP2/6-311-l-l-G(d,p), and the five lowest energy structures are shown in Table 3.15. Using laser ablation molecular beam Fourier transform microwave spectroscopy, they identified six conformers present in the gas phase. Comparing the computed rotational constants and nuclear quadrupole coupling tensor components with the experiment, they were able to decidedly match up all six experimental conformers with computed structures. Of the five low energy conformers listed in Table 3.15, four of them were identified in the experiment. 

Alonso et al. examined the glycine-one water complex using laser ablation molecular beam Fourier-transform microwave spectroscopy. By comparison of the observed rotational parameters and those predicted from an MP2/6-311+G(d,p) optimization, they concluded that the only observed isomer is that formed of the neutral isomer and water, 44a. Balabin examined the glycine-one water complex using IR spectroscopy. While he too found 44a, he was able to detect a small amount of 44b and 44c. An interesting side note is that anharmonic corrections were necessary in order to match up the computed (MP2) frequencies with the experimental values. These experiments indicate that more than one water molecule is needed to stabilize the zwitterion tautomer. 

Lopez JC, Pena MI, Sanz ME, Alonso JL (2007) Probing thymine with laser ablation molecular beam Fourier transform microwave spectroscopy. J Chem Phys 2007 126... 

Similar to 2DR, ribose (C5H5O5) is one of the most important monosaccharides since it constitutes a subunit of the backbone of RNA. NMR studies have shown that ribose in solution is a mixture of a- and p-pyranose and a- and p-furanose forms, the p-pyranose form being predominant. The recently settled crystal structures have shown that the a- and P-pyranose forms are present in the solid phase [239-243]. The structure in the gas phase has been experimentally investigated using a laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MBFTMW) technique [62]. The high resolution rotational spectrum has provided structural information on a total of six rotamers of ribose, three belonging to the a-pyranose forms and other three to the P-pyranose forms. Recently, D-ribose (m.p. 95°C) has been submitted to a laser ablation broadband (CP-FTMW) spectroscopic study and eight conformers (two new a-pyranose forms) have been identified. A broadband section of the spectra is shown in Fig. 35 and the detected conformers depicted in Fig. 36. 

Laser-Ablation Molecular-Beam Fourier Transform Microwave (LA-MB-FTMW) Spectroscopy... 

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