Vibrational cooling

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.

Hill J R, Chronister E L, Chang T-C, Kim H, Postlewaite J C and DIott D D 1988 Vibrational relaxation and vibrational cooling in low temperature molecular crystals J. Chem. Phys. 88 949-67... 

Chang T-C and DIott D D 1988 Picosecond vibrational cooling in mixed molecular crystals studied with a new coherent Raman scattering technique Chem. Phys. Lett. 147 18-24... 

Chang T-C and DIott D D 1989 Vibrational cooling in large molecular systems pentacene in naphthalene J. Chem. Phys. 90 3590-602... 

The vibrational temperature, defined for a diatomic harmonic oscillator by the temperature in Equation (5.22), is considerably higher because of the low efficiency of vibrational cooling. A vibrational temperature of about 100 K is typical although, in a polyatomic molecule, it depends very much on the nature of the vibration. 

This vibrational cooling is sufficient to stabilize complexes that are weakly bound by van der Waals or hydrogen-bonding forces. The pure rotational spectra and structure of species such as... 

It might be thought that the small number of molecules in a typical supersonic jet or beam would seriously limit the sensitivity of observation of the spectra. Flowever, the severe rotational cooling which may be produced results in a collapsing of the overall intensity of a band into many fewer rotational transitions. Vibrational cooling, which greatly increases the population of the zero-point level, concentrates the intensity in few vibrational transitions, and these two effects tend to compensate for the small number of molecules. 

Figure 4. Low-lying electronic energy surfaces of I2. These states are labeled X, A/A B, and states. The processes a, P, and y denote vibrational cooling along the X potential, geminate recombination through the states A/A, and nongeminate recombination, respectively.

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 picosecond TR experiments described above for BR reveal that a hot unrelaxed J intermediate with a highly twisted structure forms and then vibrationally cools and conformationally relaxes within 3ps to form the K intermediate. Subsequently, an isomerization induced protein conformational change takes place during 20-100 ps to produce the KL inermediate. ... 

Pecourt J-ML, Peon J, Kohler B (2001) DNA excited-state dynamics ultrafast internal conversion and vibrational cooling in a series of nucleosides. J Am Chem Soc 123 10370... 

Another remarkable aspect of LF, seen in the simulations, is that it can actually vibrationally cool the molecules. In particular, this means that the average internuclear separation Ravg should decrease as a function of increasing intensity (Fig. 1.6). This is exactly what we observe experimentally in Fig. 1.7, even as the amplitude of the vibrations is increasing [29]. 

V. B. Ivleva, Y. N. Elkin, B. A. Budnik, S. C. Moyer, P. B. O Connor, and C. E. Costello, Coupling thin-layer chromatography with vibrational cooling matrix-assisted laser desorption/ ionization Fourier transform mass spectrometry for the analysis of ganglioside mixtures, Anal Chem., 76 (2004) 6484-6491. 

Atomic- Vapor Laser Isotope-Separation. Although the technology has been around since the 1970s, laser isotope separation has only recently matured to the point of industrialization. In particular, laser isotope separation for the production of fuel and moderators for nuclear power generation is on the threshold of pilot-plant demonstrations in several countries. In the atomic vapor laser isotope-separation (AVLIS) process, vibrationally cooled 235U metal atoms are selectively ionized by means of a high power (1—2 kW) tunable copper vapor or dye laser operated at high (kHz) repetition rates (51,59,60). 

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