Absorption frequencies, spread

In conclusion, it is worth reiterating that the anomalous absorption effects described here may be manifest in any experiments that employ sufficiently high-intensity broadband radiation. To this extent, anomalies may be observable in experiments not specifically involving USES light. In particular, the continued advances in techniques of laser pulse compression have now resulted in the production of femtosecond pulses only a few optical cycles in duration (Knox et al. 1985 Brito Cruz et al. 1987 Fork et al. 1987) which necessarily have a very broad frequency spread, as the time/energy uncertainty principle shows. Thus, mean-frequency absorption may have a wider role to play in the absorption of femtosecond pulses. If this is correct, it raises further questions over the suitablity of absorption-based techniques for their characterization. 

Therefore, the absorption line is massively inhomogeneously broadened at low temperature. An inhomogeneous lineshape can be used to determine the static or quasistatic frequency spread of oscillators due to a distribution of environments, but it provides no dynamical information whatsoever [94, 95]. As T is increased to 300 K, the absorption linewidth decreases and increases. At 300 K, the lineshape is nearly homogeneously broadened and dominated by vibrational dephasing, because fast dephasing wipes out effects of inhomogeneous environments, a well known phenomenon termed motional narrowing [95]. 

The aim of this type of investigation has been the better characterization of protein spectra, in terms of their constituent aromatic amino acids, by increasing the degree of resolution of the fine structure of the latter and hence making their identification and differentiation more -certain. This effect of low temperature results from the stabilization of internal Stark and Zeeman effects, which are the chief temperature-sensitive factors determining the frequency spread of absorption bands. Sinsheimer et al. (1950) give a brief review of the subject in relation to organic compounds. 

Fig. I. Two limiting cases of resonance scattering, (a) If the incident light (dark band) has a frequency spread much larger than the absorption bandwidth of the resonant state (white band), the emitted (scattered) light decays exponentially in time with the characteristic decay time of this resonant molecular state. This is the resonance fluorescence limit, (b) If the incident light is much narrower than the absorption band, the scattered light follows the time dependence of the incident light. This is the Rayleigh and Raman scattering limit.

When a beam of electromagnetic radiation with a continuous frequency distribution is made to pass through a gaseous element or metallic vapor, certain frequencies will get absorbed. These frequencies correspond to the allowed excited states. Similarly the atomic nuclei will absorb the y-rays as the atomic excited states fall in the y-region. The important aspect of such absorption is that it is very sensitive to the y-ray energy in the sense that if the y-ray has frequency different from resonance by one part in 10, it will not be absorbed. Such sensitivity will not be realized unless the natural frequency spread (line width for atomic systems) of the y-ray is small which will happen if the life time of the excited state emitting the y-ray is long (>10 s). 

Davison [15] and by Swern et al. whilst Minkoff reproduces a few additional spectra without comment on the carbonyl frequencies. These compounds show only a single carbonyl absorption in the overall range 1790—1740 . Davison finds a rather wider frequency spread than do Swem et al., who found a considerable number of peracids absorbing at 1747—1748 cm . This frequency did not change appreciably on passing from the solid phase into solution, confirming that these acids exist in intramolecularly bonded forms. 

Figure 2. Qualitative illustration of the origin of the broad lines in the NMR spectra of abundant spins in solids. (a) A nuclear magnetic moment, sees a net local field arising from all the other spins, typified by iy (b) The resonance absorption is spread out over a range of frequency due to the spread of local field values, largely determined by the statistics of spin-up and spin-down states.

Part—IV has been entirely devoted to various Optical Methods that find their legitimate recognition in the arsenal of pharmaceutical analytical techniques and have been spread over nine chapters. Refractometry (Chapter 18) deals with refractive index, refractivity, critical micelle concentration (CMC) of various important substances. Polarimetry (Chapter 19) describes optical rotation and specific optical rotation of important pharmaceutical substances. Nephelometry and turbidimetry (Chapter 20) have been treated with sufficient detail with typical examples of chloroetracyclin, sulphate and phosphate ions. Ultraviolet and absorption spectrophotometry (Chapter 21) have been discussed with adequate depth and with regard to various vital theoretical considerations, single-beam and double-beam spectrophotometers besides typical examples amoxycillin trihydrate, folic acid, glyceryl trinitrate tablets and stilbosterol. Infrared spectrophotometry (IR) (Chapter 22) essentially deals with a brief introduction of group-frequency... 

Dust around the carbon star shows an excess emission feature between about 10.2 and 11.6 jam, clearly distinguishable in both shape and position from the 9.7-jum feature of the oxygen star, which has been attributed to small SiC particles. These particles cannot be spherical, however. According to the discussion in Section 12.2, shape effects spread an absorption band in small particles of materials like SiC between the transverse (to,) and longitudinal (to,) optical mode frequencies these frequencies for SiC are indicated on the figure. This point was made by Treffers and Cohen (1974) using Gilra s unpublished calculations. To illustrate this further, calculations for a random distribution of... 

For a linear space dependence of the Larmor frequency, the spatial resolution 1/Ax is related to the width of the NMR absorption line or the spread Av = Acot/lit in Larmor frequencies col according to (1.1.7) by... 

The inclusion of only two Bom-Oppenheimer states in our derivation is warranted if the one-photon absorption process is resonant with the electronic transition frequency. (Two-photon and multiphoton absorption processes are assumed to be nonresonant.) However, at the same time the pulse must be broad enough in frequency to include the spread of Franck-Condon-allowed vibrational levels. 

The reason for analyzing the displacement into in-phase and 90"-out-of-phase components is that their amplitude spectra represent the variation of refractive index and power absorption with frequency of the incident radiation. The "dispersion" spectrun is so named because it is the variation of refractive index with frequency that leads to the spreading out ("dispersion") of white light by a prism. 

The peak frequencies of both the vibronic and CT absorptions are in excellent agreement with the observed ones. The relative values of the integrated intensities are also well reproduced, although the width of the calculated CT band is narrower than the observed one and, correspondingly, the peak conductivity is higher. This is likely related to the fact that the interaction between tetramers in the TMTSF chain spreads each tetramer state into a band [26]. 

This model explains why SEIRA is observed in both s- and p- polarized IRRAS [384] and ATR [391, 405] spectra and in normal-incidence transmission spectra [377] and why the enhancement is not uniformly spread over each metal island but occurs mainly on the lateral faces of the metal islands [378, 384, 385]. The quasi-static interpretation of the SEIRA also defines the material parameters necessary for excitation and observation of SPR (1) The resonance frequency determined from the general Mie condition must be as low as possible and (2) Ime((Ures) must be as small as possible. The maximum enhancement effect should be observed for the absorption bands near the Mie (resonance) frequency of the particle. As mentioned in Section 3.9.1, the resonance frequencies of metal particles lie in the visual or near-IR range. However, they can be shifted into the mid-IR range by (1) increasing the aspect ratio of the ellipsoids, (2) adding the support to an immersion medium, (3) coating the particles by a dielectric shell [24, 406], or (4) varying the optical properties of the support [24, 349, 350, 384]. As emphasized by Metiu [299], the surface enhancement effect is not restricted to metals but can also be observed for such semiconductors as SiC and InSb. 

Linewidth Frequency or wavelength spread over which emission, absorption, and gain occur in the laser amplifier. 

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