Ethane, ionization spectrum

In the cyclophane 1, although the overlap between the n-system (2p) and the bridging cr-bonds (2s2p) is most effective, these orbital energy levels match worst, the first ionization potentials being 9.25 eV for benzene and 12.1 eV for ethane. As a result, the HOMOs are the almost pure it MOs with the b2g and b3g combinations. Both the PE spectrum and theoretical calculation demonstrate the degeneracy of the two HOMO levels. The absorption bands are attributed to the 17-17 transitions associated with the HOMOs. 

A typical determination is that of Lossing and Tickner for the methyl radical. Methyl radicals were produced by the pyrolysis of mercury dimethyl diluted by helium, and the mass spectrum showed that only CH3, mercury, ethane and a trace of methane were formed. Sensitivity calibrations were obtained in the usual way for the stable substances, and then the net peak at mass 15, after subtraction of the contributions from mercury dimethyl, ethane and methane, was determined. At high temperatures of pyrolysis, where the methyl radicals were most abundant, the sensitivity for the mass 15 peak of the methyl radical could then be calculated on the basis of 100 % carbon balance. As discussed earlier, wall reactions may lead to appreciable disappearance of the radical under observation, and such effects must be taken into account when calculating the sensitivity of the apparatus. Corrections of these kinds were applied to the experiments described above when Ingold and Lossing discovered that part of the methane observed was produced by reaction in the ionization chamber. The smallest relative concentration of radicals which can be determined accurately i.e. where several species give rise to the... 

The first ionization potential of ethane was measured by photoionization techniques more than 30 years ago [56-62] and it was found to be between 11.4 and 11.65 eV. Some indication of vibrational fine structure was found by Chupka and Berkowitz [62]. The classic Hel photoelectron spectrum of ethane was recorded by liirner s group (Baker et al. [25, 57] it is reproduced on Figure 3. 

Moreover, it is remarkable that at least four bands in the photoelectron spectrum exhibit vibrational fine structure. Thus, the ion possesses as many stable excited states. Only one of them, the first one is due to ionization from a n-orbital. (This makes the fine structure observed in both the photoelectron and electronic spectra of ethane less surprising.) Vy, U2. and V3 are Raman active, but v is both Raman and infrared inactive and its frequency had to be determined by indirect methods (ref. 96). 

The correspondence between the photoelectron spectrum and the ethane breakdown graph in Fig. 8 is obvious. The appearance of C2H4 and C2H5 corresponds to the first minimum in the photoelectron spectrum. Formation of C2H3 and C2H2 corresponds to ionization of a (tc -h n) electron. 

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