Collisional energy transfer probabilities in the deactivation of highly vibrationally excited aromatics

Full sets of experimentally determined ''collisional energy transfer probability distributions'', P(E', E), have become available first time for the deactivation of highly vibrationally excited large molecules. These data from KCSI measurements (kinetically controlled selective ionization) on the vibrational relaxation of toluene ([E(0)] = 50000 cm(-1)) and azulene ([E(0)] = 30000 and 20000 cm(-1)) are discussed with emphasis on systematic aspects. Under proper conditions the KCSI measurements become self-calibrating. This provides i.a. very high quality results on (Delta E), free from possible calibration errors. Detailed second moments are given and consequences on energy distributions during relaxation are discussed. The P(E',E) distributions show extended wings of finite probabilities for transfer of large Delta E. Their relative role is characterized. A double-exponential representation of P(E',E) is useful, mainly for atomic and shall molecular collider gases. However, a more universal and better analytical representation of P(E',E), using one parameter less, is recommended. The fraction of ''super-collisions'' (independent from details of definition) is very small.