Absorption of infrared photons

Thermal Transducers Infrared radiation generally does not have sufficient energy to produce a measurable current when using a photon transducer. A thermal transducer, therefore, is used for infrared spectroscopy. The absorption of infrared photons by a thermal transducer increases its temperature, changing one or more of its characteristic properties. The pneumatic transducer, for example. 

The process of dissociation by fhe absorption of infrared photons clearly involves fhe simulfaneous absorption of many photons - of fhe order of 30, depending on fhe dissociation energy and fhe photon energy - and is called multiphofon dissociation. 

Absorption of infrared photons identification of lowest energy pathway, 35,36f... 

Just as the absorption of UV or visible light causes electrons to excite between different electronic quantum states, so absorption of infrared photons causes excitation between allowed vibrational states, and absorbing microwave radiation causes excitation between allowed rotational states in the absorbing molecule. As a crude physical representation, these quantum states correspond to different angular velocities of rotation, so absorption of two photons of microwave radiation by a molecule results in a rotation that is twice as rapid as following absorption of one photon. 

Molecules also acquire vibrational energy by the absorption of infrared photons. In contrast to visible and ultraviolet radiation, the energy provided by a single infrared photon is usually much less than the unimolecular threshold energy. However, by using a sufficiently intense monochromatic radiation source such as an infrared laser, a... 

In BIRD [32], ions are activated by absorption of infrared photons emitted by nearby materials. The vacuum chamber surrounding the ICR cell, when heated normally, emits infrared radiation. This thermal infrared radiation is absorbed by the precursor ions and they are heated close to the temperature of the chamber. As a result, the precursor ions fragment via the lowest energy pathways. Temperatures of up to 500 K are accessible by this method. The rate of dissociation of peptides and proteins at these temperatures is slow and it typically takes 10-1000 s to acquire a BIRD mass spectrum. In addition, long times are needed for the temperature of the ICR cell to equilibrate with that of the vacuum chamber. Unlike SORI-CID, the BIRD technique is neither troubled by the presence of blind-spots in the resulting mass spectra (there is no resonant excitation of product ions), nor are the product ions formed off-axis. 

The Fourier-transform infrared system (FTIR) is a well-known spectroscopic technique based on the absorption of infrared photons that excite vibrations of molecular bonds. Molecules such as UsOg, UO2, UO3, Th02, have characteristic absorption bands in the infrared region that can be used like a fingerprint to detect their respective presence. FTIR radiometry has become a relatively mature and reliable method for the identification and measurement of chemicals emitted from stacks and its potential for passive standoff detection of nuclear material is under investigation (Puckrin and Theriault 2006). 

One can also see from the relative heights of the density and order parameter components in Figures 2.3a and 2.3b that the overall response of the nematic film is different for the two forms of excitatioa The absorption of infrared photons (A, = 10.6 pm) corresponds to the excitation of the ground (electronic) state s rovibrational manifold, whereas the visible photoabsorption (k = 0.53 pm) corresponds to the excitation of the molecules to the electronically excited states (see Fig. 2.5). The electronic molecular stractures of these two excited states are different and may therefore account for the different dynamical response behavior of the order parameter, which is dependent on the intermolecular Coulombic dipole-dipole interaction. From this observation one may conclude that the dynamical grating technique would be an interesting technique for probing the different dynamical... 

We note that the formalism presented here plays a major role in infrared spectroscopy. The process that gives rise to a fundamental line in the infrared spectrum of a molecule is the absorption of a photon whose frequency corresponds to that of one of the normal modes, and the simultaneous transition of this mode from the ground state (n = 0) to the first excited state. 

Many molecules which have absorption bands in the wavelength region of existing laser lines can be excited by absorption of laser photons into single isolated rotational-vibrational levels of the electronic ground state 1W>-103) (jn the case of infrared laser lines) or of an excited electronic state (with visible or ultraviolet lines)... 

Figure 17.8 Two-photon photodynamic therapy (PDT) (a) simultaneous absorption of two near-infrared (NIP) photons raises the sensitizer to the S, excited state (b) sequential absorption of two photons, one from S0 and the other from T, raises the sensitizer to a higher excited state...

The absorption or reflection by the solid sample of photons of various energies, from the ultraviolet to the infrared regions, are probably the most accessible and widely used techniques [8]. Absorption of infrared radiation by mulls or dispersions in alkali-halide discs are standard procedures. The sample holder may be capable of being heated so that peaks of interest can be monitored during the progress of decomposition. Hisatsune et al. [9] have successfully used infrared measmements to follow the decompositions of metal carboxylates (Chapter 16) incorporated in KBr discs. Spectra of powders may differ significantly from those of the same material in the form of larger crystals. 

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