Ionized electron spectrum

Figure 8. Photoelectron spectrum (PES) and Penning ionization electron spectrum (PIES) of nitric oxide radical. Average vibrational energy spacing of the first band amounts to 285 and 284 cm", respectively (104).

Figure Bl.6.12 Ionization-energy spectrum of carbonyl sulphide obtained by dipole (e, 2e) spectroscopy [18], The incident-electron energy was 3.5 keV, the scattered incident electron was detected in the forward direction and the ejected (ionized) electron detected in coincidence at 54.7° (angular anisotropies cancel at this magic angle ). The energy of the two outgoing electrons was scaimed keeping the net energy loss fixed at 40 eV so that the spectrum is essentially identical to the 40 eV photoabsorption spectrum. Peaks are identified with ionization of valence electrons from the indicated molecular orbitals.

It is well known that the electron-impact ionization mass spectrum contains both the parent and fragment ions. The observed fragmentation pattern can be usefiil in identifying the parent molecule. This ion fragmentation also occurs with mass spectrometric detection of reaction products and can cause problems with identification of the products. This problem can be exacerbated in the mass spectrometric detection of reaction products because diese internally excited molecules can have very different fragmentation patterns than themial molecules. The parent molecules associated with the various fragment ions can usually be sorted out by comparison of the angular distributions of the detected ions [8]. 

A normal, routine electron ionization mass spectrum represents the m/z values and abundances of molecular and fragment ions derived from one or more substances. 

Indazoles have been subjected to certain theoretical calculations. Kamiya (70BCJ3344) has used the semiempirical Pariser-Parr-Pople method with configuration interaction for calculation of the electronic spectrum, ionization energy, tt-electron distribution and total 7T-energy of indazole (36) and isoindazole (37). The tt-densities and bond orders are collected in Figure 5 the molecular diagrams for the lowest (77,77 ) singlet and (77,77 ) triplet states have also been calculated they show that the isomerization (36) -> (37) is easier in the excited state. 

As discussed in Section 3.2.1, an electron ionization (El) spectrum arises from a number of competing and consecutive fragmentation reactions of the molecular... 

Figure 2.19 Comparison between the electron ionization mass spectrum obtained in my laboratory (a) and that reported in the NIST library 35] (b) of nonacosan 15 one...

The electronic spectrum of the complex consists of a combination of the spectra of the parent compounds plus one or more higher wavelength transitions, responsible for the colour. Charge transfer is promoted by a low ionization energy of the donor and high electron affinity of the acceptor. A potential barrier to charge transfer of Va = Id — Ea is predicted. The width of the barrier is related to the intermolecular distance. Since the same colour develops in the crystal and in solution a single donor-acceptor pair should be adequate to model the interaction. A simple potential box with the shape... 

Sodium valproate was not sufficiently volatile for mass spectral analysis. The mass spectrum of valproic acid as shown in Figure 5 was obtained using an Associated Electrical Industries Model MS-902 Mass Spectrometer with the ionization electron beam energy at 70 eV. High resolution data were compiled and tabulated with the aid of an on-line PDP-11 Computer. 

Quite often a normal electron ionization mass spectrum appears insufficient for reliable analyte identification. In this case additional mass spectral possibilities may be engaged. For example, the absence of the molecular ion peak in the electron ionization spectrum may require recording another type of mass spectrum of this analyte by means of soft ionization (chemical ionization, field ionization). The problem of impurities interfering with the spectra recorded via a direct inlet system may be resolved using GC/MS techniques. The value of high resolution mass spectrometry is obvious as the information on the elemental composition of the molecular and fragment ions is of primary importance. 

Fig. 11.4. Electron ionization mass spectrum of nonanal. Unlike the previous example (toluene, Fig. 11.3), this 9-carbon alkyl aldehyde displays extensive fragmentation and a very low abundance molecular ion at mlz 142. The extensive degree of fragmentation exhibited by many compounds under El conditions makes manual interpretation complex and tedious. Consequently, computerized searches of spectral libraries find extensive use in compound identification.

Fig. 19.8. Electron ionization mass spectrum of toluene (top panel) from GC-MS analysis, and library search match (bottom panel) against the NIST library.

Fig. 1.2. Electron ionization mass spectrum of a hydrocarbon. Adapted with permission. National Institute of Standards and Technology, NIST, 2002.

Fig. 4.3. Photograph of the oscillographic output of the electron ionization TOF spectrum of xenon on a Bendix TOF-MS. The dark lines are a grid on the oscillographic screen. (For the isotopic pattern of Xe cf. Fig. 3.1.) Adapted from Ref. [20] with permission. Pergamon Press, 1959.

The electron impact ionization mass spectrum of cortisone acetate was obtained using solid probe introduction, using a Shimadzu QP-Class-5000 gas chromatography mass spectrometer system. The most prominent ions observed, and their relative intensities, are shown in Table 6. 

The compound represented by an electron-impact spectrum and a chemical-ionization (methane) spectrum is an ester of a long-chain, aliphatic alcohol. Interpret the spectra and identify the compound. 

Each mass spectrum has a story to tell. The molecular ion, M+ , tells us the molecular mass of an unknown. Unfortunately, with electron ionization, some compounds do not exhibit a molecular ion, because M+ breaks apart so efficiently. However, the fragments provide the most valuable clues to the structure of an unknown. To find the molecular mass, we can obtain a chemical ionization mass spectrum, which usually has a strong peak for MHH. 

Figure 22-8 Electron ionization mass spectrum (70 eV) of 1-bromobutane. [From A. lilies, R B. Shevlin, G. Childers, M. Peschke, and J. Tsai, Mass Spectrometry for Large Undergraduate Laboratory Sections," J. Chem. Ed. 1995, 72, 717. Referee from Maddy Harris.]...

Exercise 27-11 The chemical-ionization mass spectrum produced from octadecane (C18H38) by attack of the ions produced by electron impact on CH4 is shown in Figure 27-14. 

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