Mid-infrared region

It is the mid-infrared region that is used for the study of molecular vibrations and is therefore of greatest importance in the present context. The first studies in the mid-IR on catalysis were by Eischens and Pliskin (1958) whose review is still a standard work of reference. 

Infrared spectroscopy is the most common form of vibrational spectroscopy. Infrared radiation falls into three categories, as indicated in Table 8.1. It is the mid-infrared region that is of interest to us. 

Infrared spectroscopy has proven to be a very informative and powerful technique for the characterization of zeolitic materials. Most infrared spectrometers measure the absorption of radiation in the mid-infrared region of the electromagnetic spectrum (4000-400 cm or 2.5-25 xm). In this region of the spectrum, absorption is due to various vibrational modes in the sample. Analysis of these vibrational absorption bands provides information about the chemical species present. This includes information about the structure of the zeolite as well as other functional... 

The VCD spectra of molecules of the form CH3C HR,R2 have been investigated in the CH stretching region (20, 57-59) and the 16(X)-900-cm mid-infrared region (59, 60). The ROA of this type of molecule has also been recorded (II-14). In particular, a-deuterated ethanol and a-phenylethane derivatives have been studied. 

The mid-infrared region is considerably more difficult to interpret than the CH stretching region. This fact again points to the fact that chromophores responsible for VCD are delocalized over the chiral frame. 

More recently, Su et al. (81) have measured the VCD in the mid-infrared region for a series of four chiral cyclophosphamides, 26, where X is either chlorine or hydrogen. They observe an absorption band that occurs between 1205 and 1225 cm in the four molecules having strong negative VCD in all cases. They refer to this band as a VCD marker band because it appears to correlate better with the absolute configuration of these molecules than does the optical rotation at the sodium D line in the visible region of the spectrum. 

Burning stars, such as those originating from Roman candles or shells (Figure 8.5), emit radiation in the ultra-violet, the visible, near-infrared and mid-infrared regions of the electromagnetic spectrum, as displayed in Figure 8.6. 

The near infrared and mid infrared regions of the spectrum encompasses radiation with wavelength raging from about 800 to 2500 nm and from 2500 nm (4,000 cm"1) to 25,000 nm (400 cm 1), respectively.1 Infrared light when absorbed increases the vibrational and rotational energy of the molecule. 

Most atmospheric visible and DV absorption and emission involves energy transitions of the outer electron shell of the atoms and molecules involved. The infrared spectrum of radiation from these atmospheric constituents is dominated by energy mechanisms associated with the vibration of molecules. The mid-infrared region is rich with molecular fundamental vibration-rotation bands. Many of the overtones of these bands occur in the near infrared. Pure rotation spectra are more often seen in the far infrared. Most polyatomic species found in the atmosphere exhibit strong vibration-rotation bands in the 1 - 25 yin region of the spectrum, which is the region of interest in this paper. The richness of the region for gas analysis... 

Jensen PS, Bak J, Andersson-Engels S. Influence of temperature on water and aqueous glucose absorption spectra in the near- and mid-infrared regions at physiologically relevant temperatures. Applied Spectroscopy 2003, 57, 28-36. 

Potassium bromide was selected as the binder because it does not have specific absorption bands in the mid-infrared region although it does absorb water readily. Water masks the OH absorption at 3400 cm"1, making interpretation of this region difficult. 

Vitrinite concentrates were analyzed in the mid-infrared region between 3800 and 450 cm"i using a spectral resolution of 2 cm"1. Four hundred scans were co-added for each sample and a ratio was... 

---