Frame spectroscopy

ID, one-dimensional 2D, two-dimensional NOE, nuclear Overhauser effect ROESY, rotating-frame spectroscopy... 

Styles, R Rotating Frame Spectroscopy and Spectroscopy Imaging. Vol. 27, pp. 45-66 Ugurbil, K., see Garwood, M. 

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

The teclmiques and applications of single molecule spectroscopy are currently in a state of rapid development, making tliis a difficult field to summarize at any given time. This contribution is, at best, a single frame of a movie... 

We find it convenient to reverse the historical ordering and to stait with (neatly) exact nonrelativistic vibration-rotation Hamiltonians for triatomic molecules. From the point of view of molecular spectroscopy, the optimal Hamiltonian is that which maximally decouples from each other vibrational and rotational motions (as well different vibrational modes from one another). It is obtained by employing a molecule-bound frame that takes over the rotations of the complete molecule as much as possible. Ideally, the only remaining motion observable in this system would be displacements of the nuclei with respect to one another, that is, molecular vibrations. It is well known, however, that such a program can be realized only approximately by introducing the Eckart conditions [38]. 

A schematic diagram showing the disposition of these essential components for the different techniques is given in Fig. 21.3. The components included within the frame drawn in broken lines represent the apparatus required for flame emission spectroscopy. For atomic absorption spectroscopy and for atomic fluorescence spectroscopy there is the additional requirement of a resonance line source, In atomic absorption spectroscopy this source is placed in line with the detector, but in atomic fluorescence spectroscopy it is placed in a position at right angles to the detector as shown in the diagram. The essential components of the apparatus required for flame spectrophotometric techniques will be considered in detail in the following sections. 

The quantum theory of spectral collapse presented in Chapter 4 aims at even lower gas densities where the Stark or Zeeman multiplets of atomic spectra as well as the rotational structure of all the branches of absorption or Raman spectra are well resolved. The evolution of basic ideas of line broadening and interference (spectral exchange) is reviewed. Adiabatic and non-adiabatic spectral broadening are described in the frame of binary non-Markovian theory and compared with the impact approximation. The conditions for spectral collapse and subsequent narrowing of the spectra are analysed for the simplest examples, which model typical situations in atomic and molecular spectroscopy. Special attention is paid to collapse of the isotropic Raman spectrum. Quantum theory, based on first principles, attempts to predict the. /-dependence of the widths of the rotational component as well as the envelope of the unresolved and then collapsed spectrum (Fig. 0.4). 

Luminescence lifetime spectroscopy. In addition to the nanosecond lifetime measurements that are now rather routine, lifetime measurements on a femtosecond time scale are being attained with the intensity correlation method (124), which is an indirect technique for investigating the dynamics of excited states in the time frame of the laser pulse itself. The sample is excited with two laser pulse trains of equal amplitude and frequencies nl and n2 and the time-integrated luminescence at the difference frequency (nl - n2 ) is measured as a function of the relative pulse delay. Hochstrasser (125) has measured inertial motions of rotating molecules in condensed phases on time scales shorter than the collision time, allowing insight into relaxation processes following molecular collisions. 

Multidimensional spectraas well as techniques including DEPT (distortionless enhancement by polarization transfer), COSY (correlated spectroscopy), and ROESY (rotating-frame overhauser enhancement spectroscopy) have been increasingly used. 

For example, clusters identified by IR spectra and extraction as Ir4(CO)i2 on y-Al203 were found by EXAFS spectroscopy to have an Ir-Ir coordination number of nearly 3, consistent with the tetrahedral structure of the metal frame EXAFS spectroscopy produces the equivalent result for sohd Ir4(CO)i2 [27]. EXAFS spectroscopy is the most appropriate method for determination of framework structures of supported clusters, but it is limited by the errors to clusters with at most about six metal atoms. Thus, it has been used to determine frameworks that are triangular (EXAFS first-shell metal-metal coordination number of 2), tetrahedral (EXAFS first-shell metal-metal coordination number of 3), and octahedral (EXAFS first-shell metal-metal... 

ROESY Rotating-frame Overhauser enhancement spectroscopy... 

A CD-ROM is attached containing a teaching course of Mossbauer spectroscopy (ca. 300 ppt frames), a selection of examples of applications of Mossbauer spectroscopy in various fields (ca. 500 ppt frames), review articles on computation and interpretation of Mossbauer parameters using modem quantum-mechanical methods, list of properties of isotopes relevant to Mossbauer spectroscopy, appendices refering to book chapters, and the first edition of this book which appeared in 1978. In subsequent printmns files are available via springer.extra.com (see imprint page). 

The conformation of the mixed p agonist/5 antagonist H-Tyr-c[-D-Orn-2-Nal-D-Pro-Gly-] in comparison to that of H-Tyr-c[-D-Orn-Phe-D-Pro-Gly-] was studied in DMSO-d6 by NMR spectroscopy and by molecular mechanics calculations [62,64]. Neither peptide showed nuclear Overhauser effects between C H protons or chemical exchange cross peaks in spectra obtained by total correlation and rotating frame Overhauser enhance-... 

In order to combat this, the rotating frame Overhauser effect spectroscopy (ROESY) techniques can be employed. An in-depth discussion of how this technique works is outside the remit of this book but suffice to say, in the ROESY methods (1- and 2-D), NOE data is acquired as if in a weak r.f. field rather than in a large, static magnetic field and this assures that all NOEs are present and positive, irrespective of tumbling rate and magnet size. It is possible that some TOCSY correlations can break through in ROESY spectra but these will have opposite phase to the genuine ROESY correlations and so should therefore not be a problem - unless they should overlap accidentally with them. A 2-D ROESY spectrum of the naphthalene compound is shown below (Spectrum 8.6). 

ROESY Rotating-frame Overhauser effect spectroscopy. A variation (one and two dimensional) on the nuclear Overhauser experiment (NOE). The techniques have the advantage of being applicable for all sizes of molecule. See Laboratory frame model. 

Systematic NMR studies of a set of heterocycles containing guanidine and thiourea structural moiety have been published by an English team <1995MRC389>. In the frame of these investigations, some imidazo- and thiazolo-[l,2,4]triazinones having the general structure 50 have been analyzed by 13C and 1SN NMR spectroscopy. The chemical shifts of some derivatives are compiled in Table 3. 

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