Rate constant vibrational relaxation

Here, y 0 represents the vibrational relaxation rate constant for the transition v — 1 -> v — 0 and is given by... 

With the same interaction model used in Eq. (130), the vibrational relaxation rate constants associated with the vibrational population transitions bv + 1 -+bv and bv bv— 1 are given by... 

For low temperature collisions with He, the fit given by the multiquantum jump model was clearly superior to that obtained using the single quantum jump model. Even so, the Av = —I process accounted for more than 70% of the total removal rate constant (a = 1.1). For transfer out of V = 23, the total removal rate constant was around 1.6 x 10" cm s at 5 K. This was roughly an order of magnitude smaller than the He vibrational relaxation rate constant at room temperature (1.7 x 10 cm s ). Part of this difference is from the change in the collision frequency. To compensate for this factor, it is helpful to calculate effective vibrational relaxation cross sections from the relationship = kv-v / v)i where v) is the average... 

Figure 5 Collated data from ref. 68 for log of -radiative decay rate of glyoxal and biacetyl relative to vibrational relaxation rate-constant a. as a function of excess triplet vibrational energy. Right-hand scale assumes a. = 0.96 x 107 s-1 Torr-1 for all...

Figare 6 Dissociation, incubation, and vibrational relaxation rate constants of the reaction N2O N2 + 0 at low pressures in At. Relaxation and inadtation data from ref. 55, dissociation data from refs. SS—S8... 

Another conclusion we can draw from equation (3.9) is that the steady reactant distribution retains some memory of the initial distribution, but we should not be misled into reading too much significance into it. In a typical static reaction experiment, where the vibrational relaxation rate constant might be 10 s and the rate constant the starting... 

Price, J. M J. A. Mack, C. A. Rogaski, and A. M. Wodtke, Vibrational-State-Specific Self-Relaxation Rate Constant. Measure-... 

Figure 24. Vibrational populations of OH( = 1-6) following electron beam irradiation of a mixture of Ar (lOTorr), 02 (0.3Torr), H2 (90mTorr) and an estimated 4mTorr of 03. Relaxation rate constants were obtained from model calculations fitted to the data and shown by the solid lines. Reproduced with permission from Ref. 73.

Rotational and vibronic relaxation rate constants tor BaO(A Z),u = 8, J = 49 in collisions with Ar t VUV fluorescence from CO(A II) following u.v. laser excitation of high vibrational levels of the ground state... 

Studies of vibrational and/or rotational energy transfer which have utilized photochemical techniques are collected in Table 14. Dzelzkalns and Kaufman have continued a series of investigations dealing with the relaxation of vibrationally excited diatomic molecules. A fast-flow chemiluminescence technique was used to measure relaxation rate constants for HF(n = 1—4) in the presence of HF, CO2, and N2. These data were combined with earlier measurements for HF(n = 5—7) and discussed in terms of V-V or V-T/R transfer. The fraction of V-V transfer in HF(n = 2— 7) + HF(u = 0) relaxation has been determined and compared with a recent measurement for HF(n = 2) and with the results of semiclassical trajectory calcula-... 

This is clearly the dramatic temperature dependence of the vibrational relaxation rates predicted by theories of multiphonon relaxation. Apparently, in this case one deals with a true multiphonon relaxation process. It is reasonable to expect that also in many other heavier diatomics and in polyatomic molecules with small rotational constants or high barriers to free rotation the multiphonon relaxation mechanism will dominate. 

So what happens if we change our consideration to a molecule of different complexity In practice, there are many variables which complicate the analysis, for not only will the and d change, but /<, and Aoo will also be different. Let us imagine a hypothetical molecule C3D3 which possesses the same internal relaxation rate constant as does cyclopropane, and which reacts to form some product with the same values of and of A. We will also assume that it has the same two moments of inertia as does cyclopropane, so that the only thing different about it is its vibrational frequencies it has 12 normal modes of vibration instead of 21, and for the purposes of this illustration, I have simply made an arbitrary deletion of nine of the original modes of the cyclopropane molecule. 

It is only recently that departures from the mixture rule in relaxation have been found and, in fact, the effects are quite marked [77.G 81.T] the reasons for this behaviour are still quite poorly understood [79.P2 81.M2], and appear to have escaped detection because they only show up at very high ratios of the inert gas to the relaxing gas concentrations. Of course, as I have argued in the discussion of Table 5.1, there is only, as yet, a tenuous connection between the observable relaxation rate constant for vibrational energy and the apparent relaxation rate constant r,-required to define the position of the fall-off on the pressure axis, and so it is unclear at the present time whether a strong departure from one... 

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