Absorption spectmm

The absorption spectmm, 0(01), is the ratio of transition probability per unit time/incident photon flux. The incident photon flux is the number of photons per unit area per unit time passing a particular location, and is... 

Note that if we identify the sum over 8-fimctions with the density of states, then equation (A1.6.88) is just Femii s Golden Rule, which we employed in section A 1.6.1. This is consistent with the interpretation of the absorption spectmm as the transition rate from state to state n. 

The last relation in equation (Al.6.107) follows from the Fourier convolution theorem and tlie property of the Fourier transfonn of a derivative we have also assumed that E(a) = (-w). The absorption spectmm is defined as the total energy absorbed at frequency to, nonnalized by the energy of the incident field at that frequency. Identifying the integrand on the right-hand side of equation (Al.6.107) with the total energy absorbed at frequency oi, we have... 

In the symmetric, three-layer interferometer, only even-order fringes are sensitive to refractive index and it is possible to obtain spectral infonnation of the confined film by comparison of the difierent intensities of odd-and even-order fringes. The absorption spectmm of tliin dye layers between mica was investigated by Muller and Machtle [M, M] using this method. 

Figure 3.16(a) shows an interferogram resulting from the infrared absorption spectmm of air in the 400-3400 cm region. The Fourier transformed spectmm in Figure 3.16(b)... 

Bromine Monofluoride. Bromine monofluoride is red to red-brown (4) and is unstable, disproportionating rapidly into bromine and higher fluorides. Therefore, the measurement of its physical properties is difficult and the values reported in Table 1 are only approximate. The uv-absorption spectmm is available (25). 

Bromine Trifluoride. Bromine trifluoride is a colorless Hquid. The commercial grade is usually amber to red because of slight bromine contamination. The molecule has a distorted T stmeture (26). Infrared spectral data (26—30), the uv-absorption spectmm (31), and vapor pressure data (32) may be found in the Hterature. 

Bromine Pentafluoride. Bromine pentafluoride is a colorless Hquid having the molecular stmeture of a tetragonal pyramid (5). The index of refraction is 1.3529 (33). Infrared spectra (13,34), the uv-absorption spectmm (35), and vapor pressure data (11) are all available. 

Chlorine Monofluoride. Chlorine monofluoride is a colorless gas that condenses to a Hquid with a slight yeUow cast and free2es to a white soHd. The infrared spectmm of gaseous chlorine monofluoride and the Raman spectmm of the Hquid have been studied (36). The uv-absorption spectmm (37) and vapor pressure data are also available (11). 

Chlorine Pentafluoride. Chlorine pentafluoride is a colorless gas at room temperature. The ir and Raman spectra of the Hquid and gas phase have been studied (34,39). The uv absorption spectmm (45) and vapor pressure data may be found in the Hterature (18). 

The existence of isotope shifts and of tunable lasers with narrow Hnewidth leads to the possibHity of separating isotopes with laser radiation (113,114). This can be of importance, because isotopicaHy selected materials are used for many purposes in research, medicine, and industry. In order to separate isotopes, one needs a molecule that contains the desired element and has an isotope shift in its absorption spectmm, plus a laser that can be tuned to the absorption of one of the isotopic constituents. Several means for separating isotopes are avaHable. The selected species may be ionized by absorption of several photons and removed by appHcation of an electric field, or photodissociated and removed by chemical means. 

The Wiesner Reaction. The reaction of lignified tissue and phloroglucinol—hydrochloric acid gives a visible absorption spectmm with a maximum at 550 nm. This has been attributed to coniferaldehyde units in lignin as the groups responsible for the color formation. 

Because, in principle, transitions can occur on light absorption to any of the many possible energy levels of the excited state from any one of the many possible energy levels of the ground state, the absorption spectmm of a chromogen at room temperature or above is virtually continuous. 

Eig. 12. Absorption spectmm of irradiated impure vitreous siUca, Heraeus fused quart2, after a radiation dose of 10 Gy (10 rad) (208). The main impurity... 

Eig. 13. Total (-) absorption spectmm and resolved (—) bands of irradiated high purity vitreous sihca (211). Measurements made on Corning Code... 

Metal oxide electrodes have been coated with a monolayer of this same diaminosilane (Table 3, No. 5) by contacting the electrodes with a benzene solution of the silane at room temperature (30). Electroactive moieties attached to such silane-treated electrodes undergo electron-transfer reactions with the underlying metal oxide (31). Dye molecules attached to sdylated electrodes absorb light coincident with the absorption spectmm of the dye, which is a first step toward simple production of photoelectrochemical devices (32) (see Photovoltaic cells). 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

Photochemical decomposition of riboflavin in neutral or acid solution gives lumichrome (3), 7,8-dimethyl all oxazine, which was synthesized and characterized by Karrer and his co-workers in 1934 (11). In alkaline solution, the irradiation product is lumiflavin (4), 7,8,10-trimethyhsoalloxazine its uv—vis absorption spectmm resembles that of riboflavin. It was prepared and characterized in 1933 (5). Another photodecomposition product of riboflavin is 7,8-dimethy1-10-foTmylmethy1isoa11oxazine (12). 

Each tetracycline possesses a characteristic uv-absorption spectmm and this property is used extensively in stmcture elucidation (12,13). This spectmm results from the contribution of two chromophores the BCD ring system gives a X at approximately 350 nm and the A-ring a X at... 

The solubilities of Li, Na, and Ca hypochlorites in H2O at 25°C ate 40, 45, and 21%, respectively. Solubility isotherms in water at 10°C have been determined for the following systems Ca(OCl)2—CaCl2, NaOCl—NaCl, and Ca(OCl)2—NaOCl (141). The densities of approximately equimolar solutions of NaOCl and NaCl ate given in several product bulletins (142). The uv absorption spectmm of C10 shows a maximum at 292 nm with a molar absorptivity of 350 cm ( 5)- Heats of formation of alkali and alkaline earth hypochlorites ate given (143). Thermodynamic properties of the hypochlorite ion ate ... 

Substance A has an absorption spectmm in one or more regions of the ultraviolet or visible spectral range. Irradiation of A at a wavelength corresponding to one of the absorption bands results in formation of substance B, which has a visible absorption spectmm different from A. Most commonly, substance A is uncolored or only slightly colored, whereas substance B is colored or appears darker than A. 

Photochromism Based on Triplet Formation. Upon absorption of light, many polycycHc aromatic hydrocarbons and their heterocycHc analogues undergo transitions to their triplet state which has an absorption spectmm different from that of the ground state (24). In rigid glasses and some plastics, the triplet state, which may absorb in the visible, has a lifetime of up to 20 seconds. 

Complexes involving larger metal clusters, eg, Au or Au2Rh, also undergo piezochromic rearrangements with rather dramatic changes in the absorption spectmm, and well-defined changes in molecular stmcture (6,7). 

In the foregoing discussion polymers have been used as a medium for smaU molecules in comparison with the crystalline state. It has also been observed that there are changes in polymeric geometry and various rotational motions introduced by pressure (10—14). These are at times reflected in the absorption spectmm (usuaUy in the ultraviolet) or in the emission spectmm and are a form of piezochromism. 

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