Collision-induced rotational state change

In conclusion, for condensed phases molecular rotations have quite a short lifetime, because of collisions. The eventual oscillations induced by the electric field are then dissipated in the liquid state leading to vibration. At collision densities corresponding to liquids the frequency of the collisions become comparable with the frequency of a single rotation, and because the probability of a change in rotational state on collision is high, the time a molecule exists in a given state is small. It is, therefore, obvious that the electric field cannot induce organization in condensed phases such as in the liquid state. 

This computational routine for predicting state-to-state probabilities has been shown to give quantitative agreement with experiment for a wide variety of collision-induced processes. These include rotational transfer (RT) [24, 26, 36, 38—40], i.e., state change within a vibrational manifold, vibration-rotation transfer (VRT) [41, 42], i.e., transitions between vibrational states and electronic energy transfer [43], i.e., transitions between discrete levels of different electronic states. An example is given in Fig. 6 in which the calculated data were computed using the... 

While collision-induced transitions in excited electronic states can be monitored through the satellite lines in the fluorescence spectrum (Sect. 8.2.2), inelastic collisional transfer in electronic ground states of molecules can be studied by changes in the absorption spectrum. This technique is particularly advantageous if the radiative lifetimes of the investigated rotational-vibrational levels are so long that fluorescence detection fails because of intensity problems. 

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