Infrared spectroscopy radiation sources

Terahertz, or far infrared spectroscopy, covers the frequency range from 0.1 to lOTHz (300 to 3cm ) where torsional modes and lattice vibrations of molecules are detected. It is increasing in use in many application areas, including analysis of crystalline materials. Several dedicated conunercial instruments are available which use pulsed terahertz radiation which results in better signal to noise than those using blackbody sources for radiation (and associated with the terminology far infrared spectroscopy). Work using extended optics of FTIR instrumentation as weU as continuous-wave source THz has also been recently reported. ... 

Emission infrared spectroscopy is used for thin films and opaque polymers. The sample is heated so that energy is emitted. The sample acts as the radiation source and the emitted radiation is recorded giving spectra similar to those of classical FTIR. In some cases, IR frequencies vary because of differences in the structures at different depths and interactions between surface and interior emissions. 

The amount of radiation used is also important. A Nernst glower is used in ordinary infrared spectroscopy. This light source emits a relatively low amount of radiation, and no destruction of the analyzed material occurs. However, Raman infrared spectroscopy employs a radiation source of much greater energy. This radiation is sufficiently energetic to cause bond disruption and some destruction of the analyzed material. 

It will be clear from this subsection that much skillful and imaginative instrument design, by a number of different groups, has been directed towards the development of far-infrared spectroscopy. Quite apart from the developments in laboratory spectroscopy, the impact on astronomy in this region of the spectrum is of major importance. A high power tunable far-infrared source can serve as the local oscillator for the detection of far-infrared interstellar radiation. We can anticipate exciting developments in this field. 

Most fundamental rotation-vibration bands are located in the mid-infrared region from 4000 - 400 cm". A few vibrational bands appear in the far infrared where purely rotational spectra of light molecules with two or three atoms are also observed. This is in contrast to heavier polyatomic molecules the study of their rotational spectra is the domain of the microwave spectroscopist who employs different equipment, particularly, monochromatic tunable radiation sources. Rotational constants determined from IR-work are therefore usually less accurate than those obtained by microwave spectroscopy. 

The first coupling of a LINAC with infrared spectroscopy has been performed by Palmese et al. in order to study in situ kinetics of radiation-induced cationic polymerization of epoxy systems. The aim of the study is to understand the curing behavior of polymers under irradiation. A UV light source and an electron beam (10 MeV pulse width of the beam from 2.5 to 10 pm) are coupled to a portable near infrared (NIR) instrument. Briefly, a portable NIR spectrometer (Control Development Incorporated, South Bend, IN, USA) is used,... 

Infrared radiation (X = 2.5-25 pm) is the energy source in infrared spectroscopy. These are somewhat longer wavelengths than visible light, so they are lower in frequency and lower in energy than visible light. Frequencies in IR spectroscopy are reported using a unit called the wavenumber (v) ... 

Infrared spectra may be obtained for gases, liquids, orsolids. For transmittance infrared spectroscopy, the sampling techniques may involve a solution, a film, amull, or a pellet, depending on the type of sample. Reflectance spectroscopy differs from transmittance spectroscopy in that infrared radiation reflected from the surface of a material is studied. With a proper sampling accessory (obtainable from commercial sources), the materials analyzed by reflectance techniques normally require little or no sample preparation. The method is non-destructive, non-invasive, and very useful for analyzing materials that are too thick or have too much absorbance to be analyzed by transmittance spectroscopy. 

The samples were characterized by means of X-ray diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), electron diffraction (ED), and Mossbauer spectroscopy. XRD analysis was carried out on a HZG-4A diffractometer by using Ni-filtered Co Ka radiation. IR-spectra were recorded on an AVATAR FTIR-330 spectrometer. TEM/ED examinations were performed with a LEO 906E and a JEOL 4000 EX transmission electron microscopes. The resonance spectra were recorded in air at 298 K and processed by using a commercial SM2201 MSssbauer spectrometer equipped with a 15 mCi Co (Rh) source. 

McDowell and coworkers (15J studied the high resolution infrared spectrum of UF5 at ambient and low temperatures. This work was followed by a series of vibrational and electronic spectroscopic studies of matrix isolated UFg (16,17,18,19,20). In the first experiments, UFg deposited in Ar or CO matrices was vibrationally characterized by infrared spectroscopy and then exposed to broadband UV radiation at 10°K. In argon, photoreduction proceeded rapidly the 619 cirri UF5 infrared peak decreased in intensity while two new peaks grew in at 584 cirri anc 561 cirri. The new peaks were assigned to the expected UF5 photolysis product and a tentative C4V structure assignment was made. The wavelength dependence of the photoreduction was studied using a monochroma-tized UV source (1 kw Hg-Xe lamp, Schoeffel 6M-250 monochromator). The relative quantum efficiency of the UF5 dissociation per unit absorbance of UFg was found to be relatively constant in the allowed B-X absorption band (250-300 nm) (T7). Radiation in the... 

---