Pump delay times

Figure 7-4. Excitation and probe pulse profiles along with pliotocxcilalion density and change in transmission as functions uf the pump-probe delay time.

Figure 7-y. Transient PM spectrum of DOO-PPV film al pump-probe delay times of 0 and I ns. Inset decay dynamics of PA bands and SE. 

Figure 5. The Fourier transformed signal AS[r, i] of I2/CCI4. The pump-probe delay times are I = 200 ps, 1 ns, and 1 ps. The green bars indicate the bond lengths of iodine in the X and A/A states. The blue bars show the positions of the first two intermolecular peaks in the pair distribution function gci-ci- (See color insert.)...

Figure 6. The Fourier transformed signal AS[r, i] of CH2I2/CH3OH. The pump-probe time delays vary between i = —250 ps and 1 ps. The pair distribution function gl-I peaks in the 3 A region. If T < 50 ns, the I—I bond corresponds to the short-lived intermediate (CH2ri), and if x > 100 ns it belongs to the (I3") ion. Red curves indicate the theory, and black curves describe the experiment.

Figure 1.4. Experimental and theoretical femtosecond spectroscopy of IBr dissociation. Experimental ionisation signals as a function of pump-probe time delay for different pump wavelengths given in (a) and (b) show how the time required for decay of the initally excited molecule varies dramatically according to the initial vibrational energy that is deposited in the molecule by the pump laser. The calculated ionisation trace shown in (c) mimics the experimental result shown in (b).

Figure 1.5. Femtosecond spectroscopy of bimolecular collisions. The cartoon shown in (a illustrates how pump and probe pulses initiate and monitor the progress of H + COj->[HO. .. CO]->OH + CO collisions. The huild-up of OH product is recorded via the intensity of fluorescence excited hy the prohe laser as a function of pump-prohe time delay, as presented in (h). Potential energy curves governing the collision between excited Na atoms and Hj are given in (c) these show how the Na + H collision can proceed along two possible exit channels, leading either to formation of NaH + H or to Na + H by collisional energy exchange.

Figure 3.5 Near-field static ((a), (b)) and transient ((c)-(e)) transmission images of a single gold nanorod (length 300 nm, diameter 30nm). Observed wavelengths are 750nm (a), 900nm (b), and 780nm ((c)-(e)). The pump-probe delay times in ((c)-(e)) are 0.60,...

Figure 3.13. Resonance Raman spectra of Sj excited state trans-stilbene in decane at delay times indicated. The pump wavelength was 292.9 nm and the probe wavelength was 585.8nm. The vertical dashed lines illustrated the substantial spectral evolution of the 1565 cm compared to the 1239cm band. (Reprinted with permission from reference [56]. Copyright (1993) American Chemical Society.)...

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. ... 

The delay time between the pump and the probe laser pulses is usually very short in these experiments. The delay time is less than 5 ns when the pump and the probe laser pulses are the same, and the delay time is as long as several hundred nanoseconds when the pump and the probe laser pulses are from two different sources. The short delay time ensures that the fragments flying with different velocities are equally sampled before they leave the detection region. Since the delay time is much shorter than the lifetime of the excited molecules (.A ), most of these molecules do not dissociate into fragments when the probe laser pulse arrives. As a result, the probe laser can easily cause dissociative ionization of the vibrationally excited molecules due to their large internal energy. 

Another method is to measure the disappearance rate of the excited parent molecules, that is, the intensity changes of the disk-like images at various delay times (therefore, at various photolysis laser positions) along the molecular beam. This is very useful when the dissociation rate is slow and the method described above cannot be applied. This measurement requires a small molecular beam velocity distribution and a large variable distance between the crossing points of the pump and probe laser beams with the molecular beam. The small velocity distribution can be obtained through adiabatic expansion, and the available distances between the pump and probe laser beams depend on the design of the chamber. For variable distances from 0 to 10 cm in our system and AV/V = 10% molecular beam velocity distribution, dissociation rates as slow as 3 x 103 s 1 under collisionless condition can be measured. 

Fig. 5. Effect of the dissociation rate on the ion image intensity distribution, (a) Simulated translational energy distribution, (b), (c) Image intensity distributions that would result from (a) if the dissociation lifetime was 0.1/rs and 15/l

Fig. 24. Ion image of photofragment (a) m/e = 98, (b) m/e = 18 from photodissociation of d. .-cl liyIboii/ono at 193 nm. The delay times between pump and probe laser pulses are 30 /is and 7 //s. respectively, (c) The translational momentum distributions of m/e = 18 (thin solid line) and 98 (thick solid line), (d) The fragment translational energy distribution for the reaction C6D5C2D5 —> C6D5CD2 + CD3.

Figure8. (a) Pump-probe spectra of (NH3)2NH+ through the A (v= 0,1,2 corresponding to 214, 211, 208 nm, respectively) states the data reveal the influence of the vibrational level probed in the experiments, (b) Pump-probe spectrum of (NH3hH+ and (NH3)sH+ with pump pulses at 208 nm and probe pulses at 312 nm A (v = 2) of the ammonia molecule. The role of cluster size is evident. The delay time is the interval between the pump and probe laser, (a) Taken with permission from ref. 65 (b) Taken with permission from ref. 68.

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]...

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