Molecule dissociation spectrum

This compound (XHIa) possesses only one potentially dissociable proton in the molecule. The spectrum of XHIa is unaltered between pH 0-7 (see curve D). As the pH... 

Figure 12 (line A) depicts the emission spectrum of hydroxy pyrene trisulfonate dissolved in diluted buffer (pH 5.0). At this pH, the ground state is fully protonated (pK0 = 7.7), but not so the first excited singlet state (pK = 0.5). The excited molecules dissociate and 95% of the emission is at the wavelength of the excited anion (515 nm). The dissociation can be prevented if the compound is dissolved in acid solution, pH < pK., such as 2MHC1 (line B). Under such conditions, we observe the emission of the neutral form with maximum at 445 nm. Upon ligation to apomyoglobin, the fluorescence of hydroxypyrene trisulfonate consists of two... 

During the dehydration process some of the water molecules dissociate under formation of an increasing amount of Bronsted acid OH groups in the supercages and the sodalite units [8]. However, the amount of these acid sites is small, as has been proved by pyridine adsorption. From IR spectra bands at 1390, 1488, 1542 and 1632 ciiT should be expected [lO]. Figure 2 (lower spectrum) proves the almost total absence of these bands. On the other hand the strong bands at 1455, 1490 and 1605 cm indicate the presence of Lewis acid sites e.g. Cu cations [lO]. The responsible band at 1455 cm splits into a doublet indicating two different Lewis acid sites which probably are due to the free Cu(ll) cations and the true Lewis acid sites or residual Na" " ions. 

These states are formed inside the continuous spectra of the total Hamiltonian and are responsible for phenomena such as resonances in electron scattering from atoms or molecules, autoionization, predissociation, etc. Furthermore, in this work we also consider as unstable states those states that are constructs of the time-independent theory of the interaction of an atom (molecule) with an external field which is either static or periodic, in which case the effect of the interaction is obtained as an average over a cycle. In this framework, the "atom - - field" state is inside the continuous (ionization or dissociation) spectrum, and so certain features of the problem resemble those of the unstable states of the field-free Hamiltonian. The probability of decay of these field-induced unstable states corresponds either to tunneling or to ionization-dissociation by absorption of one or more photons. 

The spectrum of the disc is mostly characterized by the contribution of the molecules, especially CO, which is both abundant and stable at high temperatures. Although this spectrum is not rich in lines, their likely formation in LTE and their sensiti t ity to temperature through the molecule dissociation, provides an accurate control of various models, and good estimation of abundances. Some studies of high-n emission or absorption lines (Rydberg lines) have also been undertaken. 

FI 12.42 When absorption occurs to unbound states of the upper electronic state, the molecule dissociates and the absorption is a continuum. Below the dissociation hmit the electronic spectrum has a normal vibrational structure. 

Figure A3.12.8. Possible absorption spectrum for a molecule which dissociates via isolated compound-state resonances. Eq is the unimolecular threshold. (Adapted from [4].)...

Collision-induced dissociation mass spectrum of tire proton-bound dimer of isopropanol [(CH2)2CHOH]2H. The mJz 121 ions were first isolated in the trap, followed by resonant excitation of their trajectories to produce CID. Fragment ions include water loss mJz 103), loss of isopropanol mJz 61) and loss of 42 anui mJz 79). (b) Ion-molecule reactions in an ion trap. In this example the mJz 103 ion was first isolated and then resonantly excited in the trap. Endothennic reaction with water inside the trap produces the proton-bound cluster at mJz 121, while CID produces the fragment with mJz 61. 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

Section 6.13.2 and illustrated in Figure 6.5. The possible inaccuracies of the method were made clear and it was stressed that these are reduced by obtaining term values near to the dissociation limit. Whether this can be done depends very much on the relative dispositions of the various potential curves in a particular molecule and whether electronic transitions between them are allowed. How many ground state vibrational term values can be obtained from an emission spectrum is determined by the Franck-Condon principle. If r c r" then progressions in emission are very short and few term values result but if r is very different from r", as in the A U — system of carbon monoxide discussed in Section 7.2.5.4, long progressions are observed in emission and a more accurate value of Dq can be obtained. 

A typical SSIMS spectrum of an organic molecule adsorbed on a surface is that of thiophene on ruthenium at 95 K, shown in Eig. 3.14 (from the study of Cocco and Tatarchuk [3.28]). Exposure was 0.5 Langmuir only (i.e. 5 x 10 torr s = 37 Pa s), and the principal positive ion peaks are those from ruthenium, consisting of a series of seven isotopic peaks around 102 amu. Ruthenium-thiophene complex fragments are, however, found at ca. 186 and 160 amu each has the same complicated isotopic pattern, indicating that interaction between the metal and the thiophene occurred even at 95 K. In addition, thiophene and protonated thiophene peaks are observed at 84 and 85 amu, respectively, with the implication that no dissociation of the thiophene had occurred. The smaller masses are those of hydrocarbon fragments of different chain length. 

When an ionic solution contains neutral molecules, their presence may be inferred from the osmotic and thermodynamic properties of the solution. In addition there are two important effects that disclose the presence of neutral molecules (1) in many cases the absorption spectrum for visible or ultraviolet light is different for a neutral molecule in solution and for the ions into which it dissociates (2) historically, it has been mainly the electrical conductivity of solutions that has been studied to elucidate the relation between weak and strong electrolytes. For each ionic solution the conductivity problem may be stated as follows in this solution is it true that at any moment every ion responds to the applied field as a free ion, or must we say that a certain fraction of the solute fails to respond to the field as free ions, either because it consists of neutral undissociated molecules, or for some other reason ... 

The variety of fluoride compounds that exist and the wide spectrum of their preparation methods are related to the properties of fluorine, and above all to fluorine s high electronegativity. Low dissociation energy of the fluorine molecule, F2, relatively high energies of bond formation found in most fluoride compounds, as well as fluorine s strong oxidizing ability lead, in some cases, to spontaneous fluorination. 

Irradiation of the molecular radical anion of DESO, which has a yellow color, with light of X = 350-400 nm partially restores the red color and the ESR spectrum of the radical-anion pair. Similarly to the case of DMSO-d6 a comparison of the energetics of the photodissociation of the radical anion and dissociative capture of an electron by a DESO molecule permits an estimation of the energy of the hot electrons which form the radical-anion pair of DESO. This energy is equal to 2eV, similarly to DMSO-d6. The spin density on the ethyl radical in the radical-anion pair of DESO can be estimated from the decrease in hfs in comparison with the free radical to be 0.81, smaller than DMSO-d6. 

The femtosecond spectrum of the gas-phase Nal molecule as it dissociates into the separate atoms. A peak in the lower spectrum is observed whenever the bond distance in Nal reaches a certain value. 

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