Oxygen vibrational relaxation time

Data on vibrational relaxation times from interferometric studies, reported by White and Moore (Ref 8), show the rapid decrease of relaxation time with rise of relaxation zone temperature. Addition of up to 1% H2 to C>2 is shown to reduce the relaxation time and accelerate the reaction, but not to affect the maximum density. At a pressure of 0.001 atm, about 0.8 tort, the relaxation times would be in milliseconds instead of microseconds. The induction times for exothermic reaction are inversely proportional to the square root of the product of the number of moles of oxygen ([O2]) and the number of moles of hydrogen (IH2I) Per Hter, over the entire C J/LC ] range, to a good approximation. 

E. Bauer, JChemPhys 29, 26(1958) (Vibrational relaxation times in oxygen)... 

Shock tube studies of the decomposition of Oj have revealed the presence of an incubation period which precedes the observation of a steady rate of dissociation [11, 13, 58]. The length of the incubation period at a particular temperature was related to the vibrational relaxation time for oxygen at that temperature using previously measured relaxation data [59, 60]. The decomposition has been observed in a variety of inert diluents (He, Ar, Kr and Xe) in a wide range of oxygen concentrations (1—50%) over an extensive temperature range (2850—8500°K) by several different analytical methods including ARAS [13] and the laser-beam deflection technique [11]. 

However, several items should make us continue to be wary. Most Tis for neutral small-molecule vibrational relaxations are not ultrafast events, nor, for that matter, do they involve vibrational frequencies remotely close to the few hundred cm 1 bands of typical liquids (5). More typical are the 940 ps it takes to relax the 3265 cm-1 C-H stretch in HCN (5) and the 4.4 ns required to relax the 2850 cm-1 HC1 vibration (68) when either one of these hydrides is dissolved in CCI4. Even slower relaxations are well known the 3 ms relaxation times for 02 s 1556 cm-1 vibration in liquid oxygen, for example, (69) has been the subject of much recent discussion (70-72). 

Methane is known to be a very efficient partner for the deactivation of oxygen [271,272] the bending mode v2 of CH4 (see Figure 3.17), with frequency 1526 cm-1 (18.92 x l0-2eV), closely matches the vibrational frequency of Os [1556 cm-1 (19.29 x 10-2eV)]. Since water vapor [v2 = 1595 cm-1 (19.77 x 10-2 eV)] can deactivate 02 vibrations very efficiently, it is thus not surprising that vibrational relaxation in CH4 is also greatly affected by HsO. Monkewicz [273] observed that at 310°K a 2% H20 mixture shifted the relaxation time by a factor of about 2. 

Although work remains to be done on this problem, stimulated emission pumping (SEP) experiments strongly suggests the possibility of its occurrence. The SEP studies of highly vibrationally excited oxygen show a sharp increase in the disappearance of 02(v 26) when 02(v = 0) is the collision partner [114] and the existence of a dark channel above v = 25, where molecules prepared in a given vibrational state do not cascade down the vibrational ladder [115]. A second SEP experiment demonstrated that 02(v = 0) removes 02(v 26) at a rate 25-150 times faster than N2 [113], Subsequent studies revealed that other common atmospheric constituents such as C02 cannot compete with self-relaxation [116],... 

The external manifestation of reorientation relaxation under an applied stress is the anelastic strain that accompanies a net change of orientational order. In contrast to the elastic strain, the anelastic strain develops in a time-dependent manner governed by the rate of the reorientation jump. Under a static stress, the relaxation may therefore be observed as a limited (and recoverable) creep process. Frequently, however, it is more desirable for reasons of sensitivity or convenience to observe the relaxation dynamically as a loss-peak, via internal friction measurements made as a function of temperature and/or vibration frequency. Figure 2 shows the oxygen Snoek peak in polycrystalline thin film niobium, tested in the same vibrating-reed apparatus" - used for our studies of... 

Notably 0 2 is about V2 times that for Fe. This indicates a duplication of the vibrating mass. We therefore propose that the Fe species is related to crosslinks formed by two Fc units. Whether these are bound via a bridging oxygen or something else is still unclear. We note that the Fe cannot be identified with ferrocenium. No relaxational averaging or broadening is observed. This means that the mixed valent state is fluctuating slowly (s 10 s) unlike usual mixed valence systems with much faster fluctuations. 

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