Small-area molecular spectroscopies

Small area molecular spectroscopies are obviously desirable, but there have been problems of coupling a microscope and a spectrometer and retaining high efficiency energy transfer. This was solved for Raman spectroscopy by Dalhaye and... 

Fluorescence intensity detected with a confocal microscope for the small area of diluted solution temporally fluctuates in sync with (i) motions of solute molecules going in/out of the confocal volume, (ii) intersystem crossing in the solute, and (hi) quenching by molecular interactions. The degree of fluctuation is also dependent on the number of dye molecules in the confocal area (concentration) with an increase in the concentration of the dye, the degree of fluctuation decreases. The autocorrelation function (ACF) of the time profile of the fluorescence fluctuation provides quantitative information on the dynamics of molecules. This method of measurement is well known as fluorescence correlation spectroscopy (FCS) [8, 9]. 

A vital question which remains unanswered, however, is precisely what sort of larger problems quantum chemical research should address. Historically the field has primarily dealt with problems associated with molecular spectroscopy, the methylene problem being a classic example. [4] As a result, the driving force behind nearly all methodological development in quantum chemistry has been applications involving small molecules (fewer than twenty atoms) of rather limited interest to other areas of chemistry or biochemistry. We are currently enjoying a period of symbiotic collaboration between experimentalists and quantum chemists where the fun-... 

In this part we discuss briefly some additional aspects of the algebraic approach to problems in molecular spectroscopy. However, given the intentionally introductory nature of this article, it is impossible to address all areas in this field in fact, this article is only intended to interest spectrocopists in an algebraic formulation of the rovibrational spectroscopy of small and medium-sized molecules. Moreover, this paper should signal that new routes are available for understanding the most difficult features of the spectroscopic landscape. Further references on the... 

Quantum-mechanical ab initio calculations for small molecular systems are widely used these days as an instrument in studying problems in various Helds of chemistry and molecular physics . Most studies deal with ground-state phenomena, i.e. the structure and properties of compounds, thermal reaction pathways and dynamical behavior based on this information. There has been a noticeable increase in excited-state studies in recent years, however, in particular in connection with problems in molecular spectroscopy, in ionization processes or in the detailed study of photochemical reactions, such as photodissociation, energy-transfer and charge-exchange reactions. The calculations are especially powerful for small molecules (for example, for systems up to SO electrons and six atoms other than hydrogen), and hence numerous applications are found in particular in the area of atmospheric and interstellar chemistry and in the study of combustion processes. In these Helds it is often found that experimental and theoretical studies are undertaken in close conjunction and that the two yield complementary data which, taken together, are able to clarify a process. In other instances it is not uncommon that for short-lived species the values obtained from calculations are so far the only ones available. 

The field of applications of molecular quantum dynamics covers broad areas of science not only in chemistry but also in physics and biology. Historically, due to the fact that the full quantum-mechanical simulation of molecular processes is limited to small systems, molecular quantum dynamics has given rise mainly to important applications of astrophysical and atmospheric relevance. In the interstellar medium or the Earth atmosphere, molecules are generally in the gas phase. Since many accurate spectroscopic data are available, these media have provided various prototype systems to study quantum effects in molecules and to calibrate the theoretical methods used to simulate these effects. In this context, it is not surprising that much theoretical effort is still directed toward modeling the full quantum-mechanical treatment of small molecules. Among others, one can cite the studies of the spectroscopy of water [159-161], and of the spectroscopy, photodissociation. 

Both molecular and transition dipole moment orientation can be probed within the solid state samples, especially upon combining structural information with polarized absorption measurements. Small-area electron diffraction experiments are also effective since they allow the orientation of crystalline regions within polymer nanofibers to be probed. Most of these techniques are already well established from the study of polymer alignment in thin-films. Improved analysis methods, which make use of combined polarized Raman spectroscopy and UV-visible absorption data, are especially worthwhile to be mentioned as valuable tools to investigate the orientational properties of light-emitting polymer systems. We will come back in depth to optical properties of polymer nanofibers in Chapter 5. 

The calculation of molecular structures and dynamics has been an area of knowledge that has advanced dramatically in the last twenty years. With the advent of more powerful computers, and their increased affordability, it is now possible to perform calculations on small-to-medium size molecules on a personal computer using ab initio methods. Our ability to do this has changed the way we interpret and analyse INS spectra. In particular, we take advantage of the fact that the intensity of the spectral lines in INS spectra is not subject to the photon selection rules, unlike infrared and Raman spectroscopy. This particular characteristic gives an increased certainty to the spectral assignments when aided by theoretical calculations. 

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