Phase-coherent chemistry

Other Excitation Schemes Phase-Coherent Chemistry... 

Since many of these developments reach into the molecular domain, the understanding of nano-structured functional materials equally necessitates fundamental aspects of molecular physics, chemistry, and biology. The elementary energy and charge transfer processes bear much similarity to the molecular phenomena that have been revealed in unprecedented detail by ultrafast optical spectroscopies. Indeed, these spectroscopies, which were initially developed and applied for the study of small molecular species, have already evolved into an invaluable tool to monitor ultrafast dynamics in complex biological and materials systems. The molecular-level phenomena in question are often of intrinsically quantum mechanical character, and involve tunneling, non-Born-Oppenheimer effects, and quantum-mechanical phase coherence. Many of the advances that were made over recent years in the understanding of complex molecular systems can therefore be transposed and extended to the study of... 

Figure 3 A frequency modulation spectrum of the 4z2<-423 transition of HDO near 143 727 MHz, phase coherently detected at twice the modulation frequency and obtained with a synchronously tuned Fabry-Perot cavity cell. This species was present in natural abundance (270 ppm) in a sample of water vapor. The sloping background is due to the nonuniform coupling of the cavity, and may be eliminated by computer analysis. (From Alder JF and Baker JG (2002) Quantitative Millimetre Wavelength Spectroscopy. Cambridge Royal Society of Chemistry reproduced by permission of the Royal Society of Chemistry.)...

Normally, only the frequency and the intensity of a light field are considered in the interaction of radiation with matter. With the availability of short-pulse radiation with well-defined phase properties it has become possible to interact coherently with matter, opening up new possibilities of controlling chemical reactions and light-matter interactions. We will here consider two aspects of this quickly evolving field coherent chemistry and interference effects profoundly changing the absorptive properties of matter. 

Polyatomic molecules provide a still richer environment for studying phase control, where coupling between different dissociation channels can occur. Indeed, one of the original motivations for studying coherent control was to develop a means for bond-selective chemistry [25]. The first example of bond-selective two-pathway interference is the dissociation of dimethyl-sulfide to yield either H or CH3 fragments [74]. The peak in Fig. 11 is indicative of a resonance embedded in an elastic continuum (case 4). 

Under the simulation conditions, the HMX was found to exist in a highly reactive dense fluid. Important differences exist between the dense fluid (supercritical) phase and the solid phase, which is stable at standard conditions. One difference is that the dense fluid phase cannot accommodate long-lived voids, bubbles, or other static defects, whereas voids, bubbles, and defects are known to be important in initiating the chemistry of solid explosives.107 On the contrary, numerous fluctuations in the local environment occur within a time scale of tens of femtoseconds (fs) in the dense fluid phase. The fast reactivity of the dense fluid phase and the short spatial coherence length make it well suited for molecular dynamics study with a finite system for a limited period of time chemical reactions occurred within 50 fs under the simulation conditions. Stable molecular species such as H20, N2, C02, and CO were formed in less than 1 ps. 

Jfl emow consider coherent control as it would apply to liquid-phase chemistry. Here, Ipoplecules of species B in solution would be subjected to laser irradiation. Since we ultimately interested in the fate of the B molecules, B is the system, and the riairiing molecules in the solution and the laser are the environment. Decoherence H Sfqcts can then arise from the collisions of the solvent with the molecule of interest, l incoherence properties of the laser that cause some loss of quantum phase... 

One important fact is that synergistic effects are also known in solid state chemistry, in the absence of reactive atmosphere. For a two-phases AOx/BOy sytem, a physical property of one component BOy, e.g., the temperature at which an allotropic transition proceeds, can be modified by the presence of AOx. In the examples of catalytic synergy we have studied in the past, we have also observed such a "solid state synergy" in inert atmosphere, which cannot be explained by anything else than cooperative transformation due to coherent interfaces. 

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