MASTER EQUATION SIMULATIONS OF THE VIBRATIONAL OVERTONE ACTIVATION OFMETHYLCYCLOPROPENE

The complete kinetic data for the vibrational overtone activation of m ethylcyclopropene have been simulated using master equation calculatio ns. The simulation included photoactivation, collisional energy transf er, and reaction into three unimolecular channels. A good fit to the S tern-Volmer plots for all the products at six different photolysis ene rgies was obtained. The fit required an adjustment of the thermal acti vation barriers input into the RRKM calculation. The best fit barriers were 12 833 cm(-1) for 2-butyne, 14547 cm(-1) for 1,3-butadiene, and 14 685 cm(-1) for 1,2-butadiene. The collisional deactivation was fit with a single exponential energy transfer distribution function with a n average amount of energy transferred down per collision of 1000 cm(- 1). This average value fit all of the Stern-Volmer plots. The product yield ratios were examined for local mode specific effects, but none w ere found. Previously obtained thermal data can be fit if log A is cha nged from 12.72 to 12.30. Stern-Volmer plots were constructed for meth ylcyclopropene diluted in helium, argon, and sulfur hexafluoride for t he Delta upsilon=6 olefinic CH stretch transition. These plots were si mulated using the same calculation parameters as mentioned earlier exc ept for those having to do with the collider gas. For these simulation s the average amounts of energy transferred down per collision were 15 0, 200, and 500 cm(-1) for helium, argon, and sulfur hexafluoride, res pectively. (C) 1996 American Institute of Physics.