Collisional deactivation of vibrationally highly excited polyatomic molecules. IV. Temperature dependence of 〈ΔE〉.

The collisional loss of energy from vibrationally highly excited toluene molecules (excitation energy 52 000 cm−1) was monitored directly by time‐resolved UV absorption spectroscopy after laser excitation. Experiments were performed in a variety of bath gases heated up to 870 K with a modulated cw CO2 laser. Comparison with experiments at 300 K yields information on the temperature dependence of the average energy 〈ΔE〉 transferred per collision. The temperature coefficient of 〈ΔE〉∝T n was found to be close to zero (n=0.0±0.2) for monoatomic and diatomic bath gases; for larger bath gases small negative n values were found (n=−0.3±0.3). The results confirm earlier experiments on the steady‐state photoisomerization of cycloheptatriene which were reevaluated. They are in marked disagreement with recent conclusions on a strong decline of 〈ΔE〉 with increasing temperature.

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