PARS spectrum

Fig. 7 (a) 2D PAR spectrum of uniformly 13C, 15N-labeled N-/-MLF-OH (structure inserted) diluted to 10% in natural abundance providing cross peaks (circled) corresponding to intemuclear 13C-13C distances of more than 4 A. (b) Simulations supporting that the transfer is dominated by the MC- H -LC third-spin assisted transfer, i.e., relayed transfer is negligible (reprinted from [45] with permission)... 

Figure 2.4 displays (a) room temperature PARS spectrum, (b) jet-cooled action spectrum, (c) REMPI spectrum of CH3NH2, and, on the right side of each panel, the respective excitation schemes. The spectra are characterized by a multiple peak structure, related to the (7-branches of different bands, and the peaks of the action spectrum show up whenever the difference frequency of the SRS laser beams matches that of a specific vibrational transition. However, whereas in the PARS spectrum two of the peaks, of the degenerate CH3 stretch, V2 (2961 cm ) and the CH3 symmetric stretch, V3 (2820 cm ), are dominant and the others quite weak, in the action spectrum all peaks carry significant intensity and, in particular, the PARS low-intensity peaks become prominent. An additional dominant peak, in both the PARS and action spectra, due to the NH2 symmetric stretch, Vj (3361 cm ), is beyond the wave number span of the figure. 

The PARS technique has been recently extended to study vibrational-rotational transitions with high resolution ( 0,005 cm ). The apparatus for this is displayed in Fig. 3.6-16 (Rotger et al., 1992). A high resolution PARS spectrum of the lower component of the Fermi resonance diad of CO2 at a pressure of 1.6 kPa (= 11 Torr) is shown in Fig. 6.1-28. This is the same spectral region as already displayed in Fig. 6.1-20 by the high... 

Figure 6.1-27 The pure rotational photoacoustic Raman (PARS) spectrum of CO2 gas at a pressure of 80 kPa (600 Torr) pump laser wavelength at 532 nm. Note the complete absence of any acoustical signal due to Rayleigh scattering (at 532 nm) (Barrett, 1981).

Figure 6.1-28 High resolution photoacoustic Raman (PARS) spectrum of the lower component of the Fermi resonance diad of CO2 at a pressure of 1.6 kPa (11 Torr). Solid line calculated spectrum -1- experimental (Rotger et al., 1992).

The schematic layout of the technique is shown in Fig. 25. The PARS method is based on the application of a CW potential modulation to the electrode during the spectral acquisition period. A PARS spectrum is recorded while the two electrode potentials of interest are being rapidly modulated, and the spectrum contains the sum information of surface species at the two modulated potentials. Later, each spectrum at individual potentials can be extracted by deconvolution. By properly choosing a series of modulating frequencies in sequence (e.g., ranging from 100 K to 1 Hz), one can obtain a... 

It can sometimes be highly advantageous to detect the SRS signal indirectly. Thus in photoacoustic Raman spectroscopy (PARS), introduced by Barrett and Berry [37], a microphone or piezoelectric transducer is used to measure the acoustic wave amplitude generated in the sample when the vibrational or rotational excitation, created by the SRS process, relaxes non-radiatively into translational (heat) energy. Figure 5.8 shows the pure rotational PARS spectrum of CO2, taken from the article by J.J. Barrett, D.R. Siebert and G.A. West in Reference [4]. Although the resolution of -0.3 cm" is not remarkable, the... 

Figure 5.8. Pure rotational PARS spectrum of CO at 500 Torr [4],...

Figure 7.8 Fourier spectrum of radial velocity fluctuations in the shear layer for unseeded flow and fully developed flow wifh microexploding droplets 1 — no par tides 2 — particles...

Figure 2.7 exhibits the PAR (a) and H action (b) spectra in the region of the N—H and C—stretch fundamentals of pyrrole, where the latter spectrum was monitored at a delay of 10 ns between the SRS and UV beams. Also shown, in... 

Even in the case of an organometallic compound par excellence, namely ferrocene, the situation is somewhat confused. The most extensive study of the electronic spectrum of this molecule is that of Scott and Becker (75), and the main observed bands are given in Table III where N— V denotes... 

Fig. 7.6. Transient absorption spectra measured at 20 ns and 5 ms, respectively, after laser excitation (Xtx = 355 nm) and difference spectrum, pH 2.3, l.OxlO-4 mol L-1 colloidal Ti02/Pt(l%)-par-ticles, absorbed photon concentration per pulse 1.6xl0-5 mol L" air-sat., adopted from [7a].

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