Nitrogen second limit

The addition of hydrogen or water vapor to the carbon monoxide-carbon dioxide system results in even greater complexity (19, 36). There are some indications that water vapor has no effect on the second limit. However, the reason for this cannot be the same as that given for the lack of a nitrogen effect. 

All the simple hydrocarbons are able to suppress the low pressure ignition of the H2 + O2 system. However, there are major differences of behaviour between methane and neopentane on the one hand, and most other hydrocarbons and related materials on the other [329—332]. With formaldehyde [333], ethane [334—336], propane [329, 337], and n- and i-butane [338] the second limit in KCl coated vessels falls more or less linearly with increasing partial pressure of additive. In the experiments of Baldwin et al. [333—338], the mole fractions, x and y, of H2 and O2, respectively, could be varied independently of each other by working with H2 + N2 + O2 mixtures and adjusting the nitrogen content appropriately. The rate of fall of the second limit at constant x was almost inversely proportional to y while at constant y and not too small x, it was almost independent of x. The limit did not change much with vessel size. The observations may be accounted for by adding reactions (1)—(lii)... 

There is general agreement that increasing the O2 /CO ratio above stoichiometric raises the second limit pressure, whilst the addition of the inert gases helium, argon, or nitrogen, lowers the partial pressure of combustible gas at the limit. Von Elbe et al. [367] found that the... 

Before 1950, it was impossible to examine the true structure of a solid surface, because, even if a surface is cleaned by flash-heating, the atmospheric molecules which constantly bombard a solid surface very quickly re-form an adsorbed monolayer, which is likely to alter the underlying structure. Assuming that all incident molecules of oxygen or nitrogen stick to the surface, a monolayer will be formed in 3 x 10 second at 1 Torr (=1 mm of mercury), that is, at 10 atmosphere a monolayer forms in 3 s at 10 Torr, or 10 atmosphere but a complete monolayer takes about an hour to form at 10 Torr. The problem was that in 1950, a vacuum of 10" Torr was not achievable lO Torr was the limit, and that only provided a few minutes grace before an experimental surface became wholly contaminated. 

It should be noted that there is a considerable difference between rotational structure narrowing caused by pressure and that caused by motional averaging of an adiabatically broadened spectrum [158, 159]. In the limiting case of fast motion, both of them are described by perturbation theory, thus, both widths in Eq. (3.16) and Eq (3.17) are expressed as a product of the frequency dispersion and the correlation time. However, the dispersion of the rotational structure (3.7) defined by intramolecular interaction is independent of the medium density, while the dispersion of the vibrational frequency shift (5 12) in (3.21) is linear in gas density. In principle, correlation times of the frequency modulation are also different. In the first case, it is the free rotation time te that is reduced as the medium density increases, and in the second case, it is the time of collision tc p/ v) that remains unchanged. As the density increases, the rotational contribution to the width decreases due to the reduction of t , while the vibrational contribution increases due to the dispersion growth. In nitrogen, they are of comparable magnitude after the initial (static) spectrum has become ten times narrower. At 77 K the rotational relaxation contribution is no less than 20% of the observed Q-branch width. If the rest of the contribution is entirely determined by... 

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