Tailored excitation experiments

An early alternative to soft pulses was the DANTE Delays Alternating with Nutation for Tailored Excitation) experiment, which used a sequence of short, hard pulses of angle a <3C 90°, followed by a fixed delay t to achieve selective excitation. Thus, the pulse sequence is (a-T), ]. Nuclei that are on resonance are eventually driven to the y axis and hence are selected, whereas those more removed from the frequency range are not affected. The sequence of hard pulses can achieve a result similar to that of soft pulses and even can be shaped by modulating the duration of the pulse lengths, but DANTE pulses lead to spectral artifacts not created by soft pulses, such as unwanted sidebands. 

Selective experiments can also be performed by the tailored excitation method of Tomlinson and Hill. The selective pulse is frequency-modulated with a function designed to yield zero effective field at the resonance offset of the neighboring nuclei. Although this technique is especially promising for studies of more-complex spin systems, its use is as yet very limited, in part because the instrumentation needed is not yet commercially available. 

Spin pinging [5.86] has been proposed as a method of using rectangular pulses in 2D homonuclear COSY experiments for tailored excitation. Using spin pinging it would be possible to select regions of overlapping multiplets which are not defined sufficiently in a standard 2D COSY spectrum because of the restricted number of data points. Probably... 

An important general point to emerge from these experiments is that tailored excitation-pulse shapes can significantly alter the mass spectrum produced by laser radiation. This approach could, therefore, provide a method for the multidimensional analysis of complex molecules, as varying ion distributions, each with different information content, can be obtained as a function of pulse shape. The use of tailored femtosecond laser pulses may, therefore, open new avenues for mass spectromettic analysis of large and biologically relevant molecules. 

To generate an exchange curve, one of the two resonances involved must be inverted selectively. By whichever technique a selective inversion is carried out, it is important that the other resonances not be perturbed. The most frequently used inversion techniques in RR experiments are a long, soft pulse or an asynchronous DANTE (delays alternating with nutation for tailored excitation) sequence. 

In the ICR cell, there is a stringent correlation of cyclotron frequency/c and m/z value. For simplicity, the very first FT-ICR experiment was therefore performed with an excitation pulse of a fixed/c tailored to fit the model analyte, methane molecular ion. [185] However, useful measurements require the simultaneous excitation of all ions in the cell, and this in turn demands for a large RF bandwidth. 

Besides homogeneous and uniform SAMs or polymer brushes, systems of tailored heterogeneity such as mixed monolayers of two or more compounds, gradients, block copolymer brushes etc. are now under investigation. Especially, the development of patterned surfaces offers the exciting possibility to perform multiple parallel experiments on a single substrate or cascade reactions. 

In this contribution, the experimental concept and a phenomenological description of signal generation in TDFRS will first be developed. Then, some experiments on simple liquids will be discussed. After the extension of the model to polydisperse solutes, TDFRS will be applied to polymer analysis, where the quantities of interest are diffusion coefficients, molar mass distributions and molar mass averages. In the last chapter of this article, it will be shown how pseudostochastic noise-like excitation patterns can be employed in TDFRS for the direct measurement of the linear response function and for the selective excitation of certain frequency ranges of interest by means of tailored pseudostochastic binary sequences. 

FT/ICR experiments have conventionally been carried out with pulsed or frequency-sweep excitation. Because the cyclotron experiment connects mass to frequency, one can construct ("tailor") any desired frequency-domain excitation pattern by computing its inverse Fourier transform for use as a time-domain waveform. Even better results are obtained when phase-modulation and time-domain apodization are used. Applications include dynamic range extension via multiple-ion ejection, high-resolution MS/MS, multiple-ion simultaneous monitoring, and flatter excitation power (for isotope-ratio measurements). 

MS/MS. The capability of trapping ions for long periods of time is one of the most interesting features of FTMS, and it is this capability that has made FTMS (and its precursor, ion cyclotron resonance) the method of choice for ion-molecule reaction studies. It is this capability that has also lead to the development of MS/MS techniques for FTMS [11]. FTMS has demonstrated capabilities for high resolution daughter ion detection [42-44], and consecutive MS/MS reactions [45], that have shown it to be an intriguing alternative to the use of the instruments with multiple analysis stages. Initial concerns about limited resolution for parent ion selection have been allayed by the development of a stored waveform, inverse Fourier transform method of excitation by Marshall and coworkers [9,10] which allows the operator to tailor the excitation waveform to the desired experiment. 

As regards the high laser field problem, extensions include the so-called two-colour experiments [589] in which coherent mixtures of two laser fields of different frequency are used to tailor the excitation. The present chapter merely provides an introduction to research on atoms in strong fields, both oscillatory and constant in time, which are rapidly developing areas of atomic and molecular physics. 

NMR experiments were carried out at 15 C on a Bruker AMX-500 spectrometer equipped with a 5 mm inverse detection probe and an X-32 computer. All ID spectra were recorded with a 5500 Hz spectral width and 8k data points. The water resonance was suppressed either by a pre-saturation irradiation or by using a tailored jump-return excitation pulse l. Phase-sensitive detection in the tl dimension of 2D experiments was achieved using the time-proportional phase incremental scheme. ... 

Further advances in the field of coherent chemistry will require improved time resolution and tunability of the laser sources in the experiments [434]. Shorter laser pulses with a pulse duration of less than 20 fs will be appropriate. The optimum control technique will be achieved by specially tailored femtosecond pulse shapes [435-439], determined by sophisticated calculations using the theories of coherent chemistry [440-444]. Finally, more elaborate polarization and multipulse excitation schemes, including chirped and ultra-short pulses, will be needed. 

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