Frequency pump probe

Time-resolved spectroscopy has become an important field from x-rays to the far-IR. Both IR and Raman spectroscopies have been adapted to time-resolved studies. There have been a large number of studies using time-resolved Raman [39], time-resolved resonance Raman [7] and higher order two-dimensional Raman spectroscopy (which can provide coupling infonuation analogous to two-dimensional NMR studies) [40]. Time-resolved IR has probed neutrals and ions in solution [41, 42], gas phase kmetics [42] and vibrational dynamics of molecules chemisorbed and physisorbed to surfaces [44]- Since vibrational frequencies are very sensitive to the chemical enviromnent, pump-probe studies with IR probe pulses allow stmctiiral changes to... 

Ultrafast TRCD has also been measured in chemical systems by incoriDorating a PEM into the probe beam optics of a picosecond laser pump-probe absorjDtion apparatus [35]. The PEM resonant frequency is very low (1 kHz) in these experiments, compared with the characteristic frequencies of ultrafast processes and so does not interfere with the detection of ultrafast CD changes. 

Figure C3.5.10. Frequency-dependent vibronic relaxation data for pentacene (PTC) in naphthalene (N) crystals at 1.5 K. (a) Vibrational echoes are used to measure VER lifetimes (from [99]). The lifetimes are shorter in regime I, longer in regime II, and become shorter again in regime III. (b) Two-colour pump-probe experiments are used to measure vibrational cooling (return to the ground state) from [1021.

Anti-Stokes picosecond TR spectra were also obtained with pump-probe time delays over the 0 to 10 ps range and selected spectra are shown in Figure 3.33. The anti-Stokes Raman spectrum at Ops indicates that hot, unrelaxed, species are produced. The approximately 1521 cm ethylenic stretch Raman band vibrational frequency also suggests that most of the Ops anti-Stokes TR spectrum is mostly due to the J intermediate. The 1521 cm Raman band s intensity and its bandwidth decrease with a decay time of about 2.5 ps, and this can be attributed the vibrational cooling and conformational relaxation of the chromophore as the J intermediate relaxes to produce the K intermediate.This very fast relaxation of the initially hot J intermediate is believed to be due to strong coupling between the chromophore the protein bath that can enable better energy transfer compared to typical solute-solvent interactions. ... 

In conventional nanosecond pump-probe dispersive TRIR experiments, also described previously, kinetic data are collected at one frequency at a time. These data can then be used to construct a series of time-resolved IR spectra. Thus, in the dispersive experiment kinetic data are used to construct spectra, and in the step-scan experiment spectral data are used to derive kinetics. 

When metals have Raman active phonons, optical pump-probe techniques can be applied to study their coherent dynamics. Hase and coworkers observed a periodic oscillation in the reflectivity of Zn and Cd due to the coherent E2g phonons (Fig. 2.17) [56]. The amplitude of the coherent phonons of Zn decreased with raising temperature, in accordance with the photo-induced quasi-particle density n.p, which is proportional to the difference in the electronic temperature before and after the photoexcitation (Fig. 2.17). The result indicated the resonant nature of the ISRS generation of coherent phonons. Under intense (mJ/cm2) photoexcitation, the coherent Eg phonons of Zn exhibited a transient frequency shift similar to that of Bi (Fig. 2.9), which can be understood as the Fano interference [57], A transient frequency shift was aslo observed for the coherent transverse optical (TO) phonon in polycrystalline Zr film, in spite of much weaker photoexcitation [58],... 

Fig. 2.16. G-mode frequency of SWNTs as a function of pump-probe time delay obtained from transient transmission measurement using a sub-10 fe pulse at 2.1 eV. From [55]...

In a pump-probe experiment, if one probes both parallel and perpendicular to the pump, one can obtain the second-rank orientation TCF in Eq. (17) [122]. Pumping and/or probing at different frequencies [44 48] allows one to measure the reorientation of different sub-ensembles of molecules. Early such experiments on HOD/D2O showed that molecules on the red side of the line exhibited a slower decay than did those on the blue side [44], although later experiments showed that this difference was only for times less that 1 ps [46]. 

Describing complex wave-packet motion on the two coupled potential energy surfaces, this quantity is also of interest since it can be monitored in femtosecond pump-probe experiments [163]. In fact, it has been shown in Ref. 126 employing again the quasi-classical approximation (104) that the time-and frequency-resolved stimulated emission spectrum is nicely reproduced by the PO calculation. Hence vibronic POs may provide a clear and physically appealing interpretation of femtosecond experiments reflecting coherent electron transfer. We note that POs have also been used in semiclassical trace formulas to calculate spectral response functions [3]. 

In Fig. 1 pump-probe transients of solutions of 6 M NaBr and 1 M NaCl in HDO D20 are presented. The probe was polarized at the magic angle (54.7°) with respect to the pump polarization to avoid the measurements being affected by the orientational dynamics of the water molecules. For solutions of NaCl, the largest amplitude is observed for pump and probe frequencies of approximately 3450 cm-1, whereas for solutions of NaBr and... 

The protons of the hydroxy groups were deuterated by dissolving BP(OH)2 in cyclohexane and shaking the solution with deuterated water for several hours. After precipitation pump-probe measurements of BP(OD)2 in cyclohexane were recorded and are compared to BP(OH)2 in Fig. 4. Both samples were excited at 350 nm and probed at 505 nm. The delay of the emission rise of about 50 fs is equal in both cases and the coherent excitation of the vibrations is identical with respect to frequencies, phases and amplitudes. The ESIPT dynamics is obviously not altered by the deuteration and the mass of the proton has no influence on the transfer speed. This excludes that tunneling of the proton determines the speed of the transfer and the measurements provide the first proof for the passive behavior of the proton in the ESIPT. 

The solvated electron in methanol. Novel time- and frequency-resolved pump-probe spectroscopy of short-lived precursors. 

Fig. 5. Dual-frequency (3-, 6-p.m) 2D-IR pump/probe of AcAlaOMe in chloroform acquired with magic angle polarization...

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