Excitation transfer collisions rotational-translational

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... 

As mentioned above, rotations play a major role in CET. Most of the CET occurs via a T/R mechanism in which the translational energy goes into rotation. This is confirmed in a detailed study of single mode excitation [14] where each mode of the benzene was pumped separately. It was found that the values of a]i are a factor of 3-5 larger than the values of d- The conclusion that rotations are the major contributors to the values of an in all specific-modes excitation energies is supported by the work of Rosenblum etal. [15] who found that in SO2 rare gas collisions, rotations are the major energy transferring mode. 

The extremely narrowband emission of a laser allows the specific excitation of molecular states. The non-Boltzmann distribution produced by the excitation process is quickly destroyed by radiation processes and collisional deactivation. The relative contribution of these different deactivation channels depends on the nature of the level excited as shown in Fig. 3. In the microwave region where rotational levels are excited, the radiative life time is very long compared to the very efficient rotational relaxation processes (R—R rotation—rotation transfer and R—T rotation—translation transfer). Therefore, the absorbed radiation energy is transformed within a few gas kinetic collisions into translational energy. The situation is similar for... 

For calculating the nonequilibrium flow of polyatomic gases, the DSMC method is currently the most widely used technique. In the DSMC approach, one usually employs some empirical models [4], which very much resemble a -BGK-type relaxation model with a constant relaxation time. There are only a few attempts due to Koura [5] and Erofeev [6], for example, which employ the so-called trajectory calculations, where a realistic modeling of inelastic collisions with translational-rotational (T-R) transfer of energy is made. These computations require enormous CPU time. For vibrational excitations, no trajectory calculations with the DSMC method have been attempted to date. The physical reality is such that the vibrational term becomes important at much higher temperature than the rotational term. For the N2 molecule the quanta of vibrational temperature is 3,340 K and the quanta of rotational temperature is 2.89 K the corresponding quanta for the O2 molecule are 2,230 and 2.1 K, respectively. 

Michaels C A, Lin Z, Mullin A S, Tapalian H C and Flynn G W 1997 Translational and rotational excitation of the C02(00°0) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene evidence for impulsive collisions accompanied by large energy transfers J. Chem. Phys. 106 7055-71... 

A molecule vibrationally excited by absorption of a laser photon can convert its excitation energy into translational (F - T transfer), rotational (F-> i ), vibrational (V- F) or even electronic energy (F- ) of the collision partners. 

Castro, T L. G. Ruiz-Suarez, J. C. Ruiz-Suarez, M. J. Molina, and M. Montero, Sensitivity Analysis of a UV Radiation Transfer Model and Experimental Photolysis Rates of NO, in the Atmosphere of Mexico City, Atmos. Environ., 31, 609-620 (1997). Crosley, D. R., Rotational and Translational Effects in Collisions of Electronically Excited Diatomic Hydrides, J. Phys. Chem., 93, 6273-6282 (1989). 

In addition to the processes just discussed that yield vibrationally and rotationally excited diatomic ions in the ground electronic state, vibrational and rotational excitations also accompany direct electronic excitation (see Section II.B.2.a) of diatomic ions as well as charge-transfer excitation of these species (see Section IV.A.l). Furthermore, direct vibrational excitation of ions and molecules can take place via charge transfer in symmetric ion molecule collisions, as the translational-to-internal-energy conversion is a sensitive function of energy defects and vibrational overlaps of the individual reactant systems.312-314... 

The photofragmentation that occurs as a consequence of absorption of a photon is frequently viewed as a "half-collision" process (16)- The photon absorption prepares the molecule in assorted rovibrational states of an excited electronic pes and is followed by the half-collision event in which translational, vibrational, and rotational energy transfer may occur. It is the prediction of the corresponding product energy distributions and their correlation to features of the excited pes that is a major goal of theoretical efforts. In this section we summarize some of the quantum dynamical approaches that have been developed for polyatomic photodissociation. For ease of presentation we limit consideration to triatomic molecules and, further, follow in part the presentation of Heather and Light (17). 

The rotational and the translational freedom appear after desorption of adsorbed molecules and each energy is kept without any disturbance before detection in the present experimental condition, since there is no collision and the lifetime of the excited states for a desorbed molecule is long. The experimental data can be analyzed by a simple model using the impulse scheme, con fi ned to the momentum transferred from the substrate to an adsorbate atom, in which the form of the excited-state PES and the transition process need not be assumed [68, 69]. The energy released from the excited state is converted to the momentum and this energy is transferred impulsively. The desorption also occurs impulsively. This simple model sheds hght on the property of the intermediate excited state, and the intermediate excited state plays an important role in the DIET process. 

For percolating microemulsions, the second and the third types of relaxation processes characterize the collective dynamics in the system and are of a cooperative nature. The dynamics of the second type may be associated with the transfer of an excitation caused by the transport of electrical charges within the clusters in the percolation region. The relaxation processes of the third type are caused by rearrangements of the clusters and are associated with various types of droplet and cluster motions, such as translations, rotations, collisions, fusion, and fission [113,143]. 

First, vibrational relaxation takes place also in low density gases. Collisions involving the vibrationally excited molecule may result in transfer of the excess vibrational energy to rotational and translational degrees of freedom of the overall system. Analysis based on collision theory, with the intermolecular interaction potential as input, then leads to the cross-section for inelastic collisions in which... 

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