Incremented delay

Two-dimensional NMR spectroscopy may be defined as a spectral method in which the data are collected in two different time domains acquisition of the FID tz), and a successively incremented delay (tj). The resulting FID (data matrix) is accordingly subjected to two successive sets of Fourier transformations to furnish a two-dimensional NMR spectrum in the two frequency axes. The time sequence of a typical 2D NMR experiment is given in Fig. 3.1. The major difference between one- and two-dimensional NMR methods is therefore the insertion of an evolution time, t, that is systematically incremented within a sequence of pulse cycles. Many experiments are generally performed with variable /], which is incremented by a constant Atj. The resulting signals (FIDs) from this experiment depend... 

Once we have acquired the data, we have two time domains (one from the normal acquisition time, the other from the incremented delay, hence the data is now 2-D ). As with normal spectra, we need to look at the data in the frequency domain. We do this by Fourier transformation, first in one dimension and then in the other. The resultant data can be portrayed or plotted in one of two different formats. 

Figure 2(B) shows an equivalent pulse scheme used for studying exchange processes in the rotating frame [22, 36-38]. As in the above experiment, the first 90° pulse, followed by the incremental delay t, creates a frequency-labeled transverse magnetization that is projected onto the rotating-frame axis (x or y) by a spin-locking pulse of duration Xm. While the magnetization is spin locked, exchange will occur. As in the previous case, the data...

S02)n clusters were excited by one and two photon absorption of the 265 nm pump pulse. The excited state clusters were then ionized at incremental delay times by the 398 nm probe pulse, allowing detection by mass spectrometry. 

Using automation software routines for the ASPECT 3000 pulse generator, we can utilize up to nine ejection/activation pulses, each combining up to four options. Mass (or frequency) information is taken from several variable user-defined lists, such that each option in each event may be used on a large number of masses. The variable mass and delay lists can be defined either via alphanumeric keyboard input, or they can be defined interactively from the spectrum via cursor. Each acceleration/ejection event can contain up to 4095 different steps. All events can be separated by fixed or incrementable delays. 

The incremental delay, Aq,and the acquisition time, t2, are Fourier transformed into frequencies, v2 and iq, respectively. ( tt/2 ) v represents a 90° pulse along the x axis. The interval 11 is of the order of microseconds t2 is of the order of seconds. 

Answer The inter-pulse increment was set to zero, producing a small, constant delay rather than an incremented delay. There is no frequency evolution between successive spectra, so this is a two-dimensional plot of a one-dimensional spectrum. It is complete with tr noise ... 

Figure 5 A Fourier-transformed signal in F2, at frequency oj2, is modulated in the indirect dimension (ti) by the incremental delay. This interferogram demonstrates how a sinusoid is created in the indirect dimension when a series of such spectra are collected. Fourier transformation of this sinusoid (along fi) would thus yield a peak with a frequency o>i in Fi.

In a 2D experiments a series of FIDs are acquired using an incremented delay tl to build up a 2D data matrix, each row of the matrix corresponding to a specific value of tl. The effect of the incremented delay is to modulate the FIDs from the experiments, which can be interpreted and analysed as a pseudo FID with respect to the time delay tl. By convention the incremented delay is called dO and the increment inO. The detected frequency range in the fl dimension is given by ASW [Hz] = l/(inO ndO ). Normally there is only one time increment variable but in special pulse sequences based upon for instance the ACCORDION-principle, see section 5.9.3, additional increment variable ini, in2... can be defined. Usually for the first experiment dO = 3 us and for the second and subsequent experiments dO = 3u -i- inO (n -1). In a number of 2D experiments the... 

Note that dO and dIO are recommended exclusively for use as the incremented delay in 2D and 3D experiments. 

Hard/shaped pulse, soft pulse, DANTE pulse train, composite pulse, cw-irradiation, cp decoupling sequence, spinlock, constant or incremented delay... 

The J-resolved experiment is based upon a spin echo and an incremented delay dO that occurs before and after the spin echo. It is the incrementation of the spin echo time that generates the second time domain and subsequently the fl dimension. How the spin... 

To improve the sensitivity the selective J-resolved pulse sequence may be combined with a refocused INEPT polarization transfer experiment. In contrast to the original heteronuclear J-resolved experiment the first excitation pulse is executed on the F2 channel with the spin-echo sequence sandwiched between two incremental delay. Coupling evolves during the second incremental delay before the refocused INEPT unit creates in-phase coherence for the nuclei which are coupled to the selected proton nucleus allowing decoupling on the F2 channel during data acquisition. 

Inversion Recovery method for Tj measurement incremented delay... 

The ID TOCSY pulse sequence can be converted into a 2D experiment by inserting an incremented delay between the excitation pulse and the spinlock sequence as shown in the scheme below. In Check it 5.4.2.3 the 2D IR TOCSY experiment is calculated and the results compared with the corresponding IH COSY experiment without and with relay step to highlight the additional correlation peaks in the TOCSY spectrum. 

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