High-resolution UV spectroscopy

Microwave spectroscopy is probably the ultimate tool to study small alcohol clusters in vacuum isolation. With the help of isotope substitution and auxiliary quantum chemical calculations, it provides structural insights and quantitative bond parameters for alcohol clusters [117, 143], The methyl rotors that are omnipresent in organic alcohols complicate the analysis, so that not many alcohol clusters have been studied with this technique and its higher-frequency variants. The studied systems include methanol dimer [143], ethanol dimer [91], butan-2-ol dimer [117], and mixed dimers such as propylene oxide with ethanol [144]. The study of alcohol monomers with intramolecular hydrogen-bond-like interactions [102, 110, 129, 145 147] must be mentioned in this context. In a broader sense, this also applies to isolated ra-alkanols, where a weak Cy H O hydrogen bond stabilizes certain conformations [69,102]. Microwave techniques can also be used to unravel the information contained in the IR spectrum of clusters with high sensitivity [148], Furthermore, high-resolution UV spectroscopy can provide accurate structural information in suitable systems [149, 150] and thus complement microwave spectroscopy. 

If the retention times of the analytes are known, or there is an efficient method for their detection on-line, such as UV, MS or radioactivity, stop-flow HPLC-NMR becomes a viable option. In the stop-flow technique, all the usual techniques available for high-resolution NMR spectroscopy can be used. In particular, these include valuable techniques for structure determination such as 2-dimensional NMR experiments which provide correlation between NMR resonances based on mutual spin-spin coupling such as the well-known COSY or TOCSY techniques. In practice, it is possible to acquire NMR data on a number of peaks in a chromatogram by using a series of stops during elution without on-column diffusion causing an unacceptable loss of chromatographic resolution. 

If the retention times of the compounds to be separated are known, or if they can be detected by using UV (including diode arrays), radiochemical or fluorescence detectors, stop-flow LC-NMR becomes an option. Upon detection, the PC controlling the liquid chromatograph allows the pumps to continue running, moving the peak of interest into the NMR probe. Once the pumps have stopped, normal high-resolution NMR spectroscopy is possible. It could be... 

F. Turatti, et ah. Positionally dependent fractionation factors in the UV photolysis of N2O determined by high resolution FTIR spectroscopy, Geophys. Res. Lett. T1 (16) (2000) 2489-2492. 

H. J. Neusser and K. Siglow, High-resolution ultraviolet spectroscopy of neutral and ionic clusters hydrogen bonding and the external heavy atom effect, Chem. Rev. 100,3921-3942 (2000). Y. Matsumoto, T. Ebata, and N. Mikami, Structures and vibrations of 2-naphthol-(NH3) (n = 1-3) hydrogen-bonded clusters investigated by IR-UV double-resonance spectroscopy, J. Mol. Struct. 552, 257-271 (2000). 

S. Svanberg High-resolution laser spectroscopy in the UV/VUV spectral region, in Applied Laser Spectroscopy, ed. by M. Inguscio, W. Demtroder (Plenum, New York 1990)... 

D.S. Leckrone, S. Johansson, G.M, Wahlgren, S.J. Adelman High resolution UV stellar spectroscopy with the HST/GHRS, challenges and opportunities for atomic physics, Phys. Scr. T47, 149 (1993)... 

There are several reports in the literature in which emission from a highly fluorescent impurity has been mistaken for weak anomalous emission. For example the emission of fluoranthene had been the subject of a long-standing controversy. Weak emission of fluoranthene at ca. 353 nm was initially interpreted as anomalous Sj - Sq emission [45,46], but this observation was not routinely repeatable [47,48]. Later, Hofstraat el al. investigated fluoranthene using high resolution ShpoTskii spectroscopy [49], and identified the near uv emission as fluorescence from a substituted phenanthrene impurity present in commercial fluoranthene samples. 

Peaks are analyzed separately by their retention times, absorption, and fluorescence properties. RCCs show absorbance maxima near A.500 and 316 nm. For FCCs, UV-Vis specna show two prominent bands near 361 and 320 mn and a luminescence maximum at 436 mn and NCCs show UV-Vis spectra with absorbance maxima near 320 and 210 nm. Nevertheless, as none of these approaches is suitable for elucidating structures, it is necessary to apply additional MS and NMR analyses to fully characterize snuctural features. Electron spray ionization (ESI) and high-resolution EAB mass spectroscopy have been applied to elucidate the molecular formulae of colorless compounds. ... 

A frequent complication in the use of an insoluble polymeric support lies in the on-bead characterization of intermediates. Although techniques such as MAS NMR, gel-phase NMR, and single bead IR have had a tremendous effect on the rapid characterization of solid-phase intermediates [27-30], the inherent heterogeneity of solid-phase systems precludes the use of many traditional analytical methods. Liquid-phase synthesis does not suffer from this drawback and permits product characterization on soluble polymer supports by routine analytical methods including UV/visible, IR, and NMR spectroscopies as well as high resolution mass spectrometry. Even traditional synthetic methods such as TLC may be used to monitor reactions without requiring preliminary cleavage from the polymer support [10, 18, 19]. Moreover, aliquots taken for characterization may be returned to the reaction flask upon recovery from these nondestructive... 

Luminescence of Pr + in zircon is very difficult to detect under UV excitation even by time-resolved spectroscopy. The reason is that it has a relatively short decay time similar to those of radiation-induced centers. Visible excitation, which is not effective for broadband luminescence, allows the revealing of Pr + luminescence lines, using high-resolution steady-state spectroscopy. Under such experimental conditions each element has individual lines, enabling confident identification of the spectrum to be possible (Gaft et al. 2000a). Only if radiation-induced luminescence in zircon is relatively weak, the lines of Pr may be detected by UV excitation (Fig. 4.38c). 

The experiments were performed in stainless steel UHV chambers which were equipped with the instrumentation necessary to perform Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), UV Photoelectron Spectroscopy (UPS), Low Energy Electron Diffraction (LEED), work function measurements (A( )), High Resolution Electron Energy Loss Spectroscopy (HREELS), and Temperature Programmed Desorption (TPD). The Au(lll) crystal was heated resist vely and cooled by direct contact of the crystal mounting block with a liquid nitrogen reservoir. The temperature of the Au(lll) crystal was monitored directly by means of a... 

Martin wrote at the end of his review in 1974 6) It is our intimate conviction that further work on these unique molecules. .. should be highly rewarding in many fields of chemistry. To our opinion this conviction is verified now because the knowledge obtained from these molecules in the field of NMR an UV-spectroscopy, resolution of enantiomers and asymmetric synthesis appears to become more generally useful in several areas of organic chemistry. 

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