Electric Discharges in a Gas

In this discussion, only inert gases such as argon or neon are used as examples because they are monatomic, which simplifies description of the excitation. The introduction of larger molecules into a discharge is discussed in later chapters concerning examination of samples by mass spectrometry. 

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The condition for observing induced emission is that the population of the first singlet state Si is larger than that of So, which is far from the case at room temperature because of the Boltzmann distribution (see above). An inversion of population (i.e. NSi > Nso) is thus required. For a four-level system inversion can be achieved using optical pumping by an intense light source (flash lamps or lasers) dye lasers work in this way. Alternatively, electrical discharge in a gas (gas lasers, copper vapor lasers) can be used. 

The technique for determining the various parameters in the relationships are so interdependent that the arguments are essentially cyclic and the relationships are mutually interdependent. Thus, the whole basis is flawed and the apparent agreement is inevitable. Also, it is tacitly assumed that the relationships for electric discharge in a gas (derived in quite different circumstances) applies to this situation. Secondly, attempts to repeat the various experiments have failed to reproduce Deryaguin s results satisfactorily. 

A third pumping method (Fig. Ic) uses an electrical discharge in a mixture of gases. It relies on electronic excitation of the first component of the gas mixture, so that those atoms are raised to an upper energy level. The two components are chosen so that there can be a resonant transfer of energy by collisions from the upper level of the first component to level 3 of the second component. Because there are no atoms in level 2, this produces a population inversion between level 3 and level 2. After laser emission, the atoms in the second component return to the ground state by collisions. 

In order to complete the list of carbon oxides C =0 (n = 1-9) it should be mentioned that, as it was already discussed for C5O, also the higher members C7O, C80, and C9O have not been yet isolated in a matrix, but they could be generated by Endo et al.134,135 in the gas phase by an electric discharge in a mixture of C3O2 and argon. The reaction products were analyzed by rotational spectra, from which the linear cumulenic structure and the bond lengths were derived. 

Figure 2 The Urey-Miller Experiment. The glass vessel to the lower left of the picture is used for the water reservoir and mimics oceans on the early Earth. An electrical discharge of a gas mixture mimicking the composition of the early Earth s atmosphere takes place in the large bulb at the top right. Molecules formed in the discharge may be condensed and are collected at the bottom ofthe system.

Bombardment of gaseous PH3/NH3 mixtures with 70 eV electrons yielded the cationic products PHNJ, PNHJ, and a minor quantity of PNH+. These ions originated most likely from the reaction of the primary ion PH+ with NH3 [32] see Section 1.1.2, p. 42, for details. Only the products of proton transfer reactions were observed at an electron energy of 12 eV [32]. The reactions occurring in PH3/NH3/H2O mixtures when subjected to electric discharges in the gas phase, are described above on p. 245. 

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