Single-pulse excitation

The molecules are excited by a short laser pulse. The trailing edge of this pulse should be short compared with the decay time of the excited level, which is directly monitored after the end of the excitation pulse. Either the time-resolved LIE on transitions k) m) to lower levels m) is detected or 

This technique of single-pulse excitation is useful for low repetition rates. Examples are the excitation with pulsed dye lasers pumped by Nd YAG or excimer lasers [11.114,11.117]. 

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SPE (1) Solid-phase extraction (2) Single-pulse excitation (NMR)... 

Single Pulse Excitation Magic-Angle Spinning... 

Fig. 8 Schematic diagrams for the following pulse sequences (A) single pulse excitation/magic-angle spinning, (B) total suppression of sidebands, and (C) delayed decoupling, or dipolar dephasing.

By making the excitation pulses overlap with the minimum of the probe pulse preceding its main maximum, the nonresonant background is further suppressed (Pestov et al. 2007). The same idea can be exploited with a single pulse excitation (Dudovich et al. 2003), when both pump pulses at frequencies i, 2 are derived from a single ultra-broadband pulse. 

Figure 12.13 shows the Xe spectra of a iPP/EP blend obtained with single pulse excitation and with => 129Xe cross-polarisation at -33 °C [13]. In the cross-polarisation spectrum only the Xe line from Xe in iPP is observed, because the dipolar interaction between the polymer spins and the 129Xe spins due to the Xe mobility is too weak in EP. Also the cross-polarisation signal of iPP disappears at temperatures higher than the Tg of iPP. 

Figure 12.13 129Xe spectra of the blend of Figure 12.7 obtained with single pulse excitation (top spectrum) and with 1H-129Xe cross-polarisation at -30 C. The crosspolarisation time was 3 milliseconds and recycle time of 3 seconds. Cross-polarisation is effective only for Xe in the iPP matrix, the Xe atoms in the EP domains are too mobile. At higher temperatures also the CP resonance of Xe in iPP disappears... 

Figure 6. Single pulse excitation and cross polarization 2 Si HHR spectra of dealuminated mordenite.

N.D. = not determined. SPE = single pulse excitation. CP = cross-polarisation... 

More direct information on the energetics of the photopolymerization process is afforded by DSC measurement with UV-initiation of the reaction. Under single pulse excitation the integral heat evolved per light pulse is a measure for the product nAH and from the ratio of the signal amplitudes at t = 0 and t -+ co, respectively,... 

The MAS NMR was performed on a JNM-ECP 300 JEOL spectrometer with a spinning rates of ca. 5.S kHz, for the understanding of the local interaction between nitrogen compound and adsorbent. IH NMR spectra was carried out at 300.53 MHz using single-pulse excitation. The n/2 pulse width and pulse delay were 4ps and 10s. 

The chemical compositions of the samples were determined by atomic adsorption spectroscopy (AAS). X-ray powder diffraction patterns were recorded after synthesis and template removal on a Siemens D5000 diffractometer using CuKa radiation. After calcination, nitrogen adsorption and desorption isotherms were measured on a Micromeritics ASAP 2010 sorption analyzer. Al MAS NMR spectra were recorded on a Bruker MSL 400 spectrometer using single pulse excitation with standard 4 mm rotors The resonance frequency was (Oo/271 = 104.31 MHz for Al using a 7t/20 pulse and a 0.5 s recycle delay. A 0.1 M solution of aluminum nitrate in water was employed as the chemical shift reference... 

Current instruments use different techniques for the attenuation measurement with static or variable width of the measuring zone, measurement in transmission or reflection, with continuous or sweeped frequency generation, with frequency burst oy. single-pulse excitation. 

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