Excitation transfer collisions Vibrational

A-B relative or external motion undergo free-free transitions (E., E. + dE.) (Ej Ej+ dE within the translational continuum, while the structured particles undergo bound-bound (excitation, de-excitation, excitation transfer) or bound-free (ionization, dissociation) transitions = (a, 3) ->/= (a, (3 ) in their internal electronic, vibrational or rotational structure. The transition frequency (s ) for this collision is... 

Returning to our A-B dissociation process, the vibrational levels of the molecule can only be excited by collisions with other molecules. Consider the energy transfer of molecule A by collision with other A molecules as a chemical reaction... 

A necessary condition for the two-term expansion of the distribution function of equation (2) to be valid is that the electron collision frequency for momentum transfer must be larger than the total electron collision frequency for excitation for all values of electron energy. Under these conditions electron-heavy particle momentum-transfer collisions are of major importance in reducing the asymmetry in the distribution function. In many cases as pointed out by Phelps in ref. 34, this condition is not met in the analysis of N2, CO, and C02 transport data primarily because of large vibrational excitation cross sections. The effect on the accuracy of the determination of distribution functions as a result is a factor still remaining to be assessed. 

Very little is known about the transfer of vibrational energy from one molecule to another, but for dissimilar species such as oxygen and ozone it would be expected to be very inefficiently transferred in such large amounts as would be required for an energy chain. It seems much more reasonable to expect vibrationally excited oxygen molecules to lose their energy preferentially in collision with other oxygen molecules... 

Unlike the case of collision-induced vibrational energy transfer, collision induced rotational energy transfer seems to be free of strong restrictions on the changes in the rotational quantum numbers. When account is taken of the spectral widths of the excitation sources used, the nature of the rotation-vibration structure in the fluorescence and absorption spectra, and the possibility of resonant ener f transfer in the collision, it is concluded that the studies of Bj aniline are the weakest, those of B2 benzene better, and those of glyoxal the best available. With this hierarchy of quality of information kept in mind, the following weaker conclusions can also be obtained from the studies cited. 

Internal conversion is a pseudo-first-order process by which the singlet excited state Sb energy is lost by collisions with solvent molecules or else by transfer between vibrational modes. Inevitably, the rate he will increase with increasing temperature and vice versa. Quenching is a similar deactivation process, in which collision with solute molecules leads to loss in singlet... 

Nitrogen molecules electronically excited through VE relaxation can produce atomic oxygen and ozone by reactions (6-72) and (6-73). The VE-relaxation processes are adiabatic, related to energy transfer from heavy particles to electrons, and therefore their probability is relatively low. The kinetics of these processes is similar to that of associative ionization of vibrationally excited molecules (2-34). Another mechanism of direct energy transfer from vibrational excitation to ozone production is related to disproportioning in the collision of vibrationally excited oxygen molecules ... 

Figure 1 Relative rate constants for vibrational energy transfer in collisions of electronically excited I2 initial vibrational state v, change of vibrational state Av. Collision partner at left O = He, = Re, from ref. 39 at right = He from ref. 40)...

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