Spectroscopic Investigations of Collision Processes

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. 

These processes have previously been explored mainly in ultrasonic experiments or in shock waves 1. Both methods, however, may thermally populate many levels of the molecules under investigation, and the interpretation of relaxation times in mixtures 

Deactivation of V3 and V4 in collisions with noble gases is less probable, since here the vibrational energy has to be converted at least partly into translational energy. In CH4-Ar collisions, for instance, the authors found TiP = (68 20) 10 secs-atm for the V3 - V4 transfer but 93 10 sec-atm for the V4 deactivation. 

A detailed description of the laser-excited vibrational fluorescence method and further results on relaxation processes in methane, including V - R transfer, have been given in reference In this paper, too, a comparison is made between the experimentally obtained F - F rates and calculations for the repulsive intermolecular potential responsible for these transitions. 

By using a Q-switched NjO laser the asymmetric stretching vibration of NaO has been excited and the relaxation rates of NjO have been measured as a function of pressure in mixtures with N2, Hj, D2 and noble gases. 

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