Absorption spectra pressure

Because of the relatively high population of the u" = 0 level the v" = 0 progression is likely to be prominent in the absorption spectrum. In emission the relative populations of the i/ levels depend on the method of excitation. In a low-pressure discharge, in which there are not many collisions to provide a channel for vibrational deactivation, the populations may be somewhat random. However, higher pressure may result in most of the molecules being in the v = 0 state and the v = 0 progression being prominent. 

Flash photolysis of either H2S [66] or H2S2 [67, 68] in the gas phase at low partial pressures produces, inter aha, HS2- radicals which were detected by their UV absorption spectrum in the 307-380 nm region. In addition, singlet and triplet 2 molecules as well as SH radicals are formed from H2S2, and the following reaction mechanism has been proposed (photolysis in the region 200-300 nm in the presence of excess CO2) [67] ... 

The electronic spectrum of S2O has been studied both in absorption and in emission and both in the ultraviolet and the visible regions. The absorption spectrum in the near UV region is extremely intense and well suited to detect S2O in gases even at very low partial pressures. Two band systems are located in the UV region at 340-250 nm and at 230-190 nm [35] while a third system in the visible region at 645-575 nm was discovered only by op-toacoustic detection [36]. The 340-250 nm system has also been observed for matrix-isolated S2O [37]. For more details see [1, 38-47]. 

The following physico-chemical properties of the analyte(s) are important in method development considerations vapor pressure, ultraviolet (UV) absorption spectrum, solubility in water and in solvents, dissociation constant(s), n-octanol/water partition coefficient, stability vs hydrolysis and possible thermal, photo- or chemical degradation. These valuable data enable the analytical chemist to develop the most promising analytical approach, drawing from the literature and from his or her experience with related analytical problems, as exemplified below. Gas chromatography (GC) methods, for example, require a measurable vapor pressure and a certain thermal stability as the analytes move as vaporized molecules within the mobile phase. On the other hand, compounds that have a high vapor pressure will require careful extract concentration by evaporation of volatile solvents. 

In applying RAIRS to CO adsorption, the contribution from CO molecules in the gas phase to the absorption spectrum at CO pressures above 10-3 mbar completely obscures the weak absorption signal of surface adsorbed CO. Beitel et al. found it possible to subtract out the gas phase absorption by coding the surface absorption signal by means of the polarization modulation (PM) technique applied to a conventional RAIRS spectrometer, p-polarised light produces a net surface electric field which can interact with adsorbed molecules, whereas both polarization states are equally sensitive to gas phase absorption because gas phase molecules are randomly oriented. By electronic filtering a differential spectrum is computed which does not show contributions from the gas phase and which has much higher surface sensitivity than a conventional RAIRS setup. 

Farhataziz et al. (1974a, b) studied the effect of pressure on eam and found that as the pressure is increased from 9 bar to 6.7 Kbar at 23° (1) the primary yield of e decreases from 3.2 to 2.0 (2) hv increases from 0.67 to 0.91 eV (3) the half-width of the absorption spectrum on the high-energy side increases by 35% and (4) the extinction coefficient decreases by 19%, which is similar to eh. The pressure effects are consistent with the large volume of ean (98 ml/M), whereas the reduction in the observed primary yield at 0.1 ps is attributable to the reaction eam + NH4+. Some of the properties of eam have been discussed by several authors in Solvated Electron (Hart, 1965). 

The absorption characteristics of PS I were measured on the four kinds of subphase surfaces during compression. As an example, Figure 2 shows the absorption spectra of the PS I monolayers on the PBV subphase surface under different surface pressures. Two absorption bands at about 420-450 and 676 nm increase with the compression, indicating the accumulation of the PS I to form a condensed monolayer. Compared to the absorption spectrum of PS I in solution (Fig. 3), the band at around 436 nm splits into two peaks. The wave-shaped small band between 470 and 630 nm is due to a low single-to-noise ratio on the water surface. These spectral features together with the jt-A isotherms indicate that PS I remains at the interface, and that the loss of PS I, due to dissolving into the subphase, is not significant [2],... 

CF2 is unique among carbenes because of its high stability and low reactivity. Investigations of the ultraviolet absorption spectrum of CF2 have led to estimates of roughly 10 milliseconds to one minute for the half-life of CF2 at pressures in the region of one atmosphere. The gas phase molecule does not react with BF3, N20, S02, CS2 or CF3I at 120 °C5 K The nature of CF2 is perhaps best presented in separate sections discussing its preparation, structure and physical properties, reaction chemistry, and reaction kinetics. 

A microwave discharge through GeCl4 vapor at low pressure produced a continuous emission from 3125 to 3341 A, the same range as that observed in the absorption spectrum of GeCl2. 

Suppose that a high hydrostatic pressure is applied to a crystal sample of sapphire (AI2 03 Ti +). How do you expect that the absorption spectrum of Ti + (Figure 5.4) will be affected ... 

One of the first applications of this chopped-beam irradiation technitriplet spectra was reported by Labhart From a knowledge of the intensity of the irradiation light, he determined the quantum yield of triplet generation to be 0.55 0.11 for outgassed solutions of 1,2-benzanthrazene in hexane at room temperature. Hunziker 32) has applied this method to the study of the gas-phase absorption spectrum of triplet naphthalene. A gas mixture of 500 torr Na, 0.3 mtorr Hg, and about 10 mtorr naphthalene was irradiated by a modulated low-pressure mercury lamp. The mercury vapor in the cell efficiently absorbed the line spectrum of the lamp and acted as a photosensitizer. The triplet state of naphthalene was formed directly through collisional deactivation of the excited mercury atoms. 

Electrons in nonpolar liquids are either in the conduction band, trapped in a cavity in the liquid, or in special cases form solvent anions. The energy of the bottom of the conduction band is termed Vq. Vq has been measured for many liquids and its dependence on temperature and pressure has also been measured. New techniques have provided quite accurate values of Vq for the liquid rare gases. The energies of the trapped state have also been derived for several liquids from studies of equilibrium electron reactions. A characteristic of the trapped electron is its broad absorption spectrum in the infrared. 

The previous sections have dealt primarily with infrared absorption spectra, although the conclusions can in general be applied to other types of spectra. Here additional uses of deconvolution will be demonstrated. In the first example, a Fourier transform spectrum is simulated and several attempts to deconvolve this spectrum show limited success. In the second example, pressure-broadening effects in an infrared absorption spectrum and a Raman spectrum are simulated. An attempt at removing these effects by deconvolution shows some promise. 

Such a process would have an intensity exponent of unity as observed. A further fact in support of the disproportionation mechanism is that the yield of CF2CI2 is largely independent of the ketone pressure at room temperature an abstraction mechanism would require a first-order dependence upon ketone pressure. While the dimer of CF2, tetrafluoro-ethylene, has never been observed in the reaction mixture, a white solid collected in the cell which was probably a polymer of CF2. While the experimental conditions are not strictly comparable, it is significant that the absorption spectrum of CF2 has been observed in the flash photolysis of 1,3-dichlorotetrafluoroacetone.39 When the temperature is raised, however, the yield of CF2C12 in normal photolysis, increases rapidly suggesting an energy of activation and this process can only be chlorine abstraction. The rate function ... 

Fig. 3.10. The rototranslational absorption spectrum of H2-H2 pairs, recorded in equilibrium hydrogen (i.e., para-Fh and ortho-FL concentrations are in thermal equilibrium proportions) at three temperatures 77.4 K ( ), 195 K (x), and 293 K ( ). Various pressures from 10 to 100 atmospheres and a 3 m absorption path length were used after [37],...

J. R Colpa and J. A. A. Ketelaar. The pressure-induced rotational absorption spectrum of hydrogen I. Molec. Phys., 1 14, 1958. 

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