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Time-resolved diode laser infrared absorptiodgain spectroscopy was used to determine relative populations of the 000 and 010 vibrational states of H20 produced in the reaction of OH with cyclohexane and cyclooctane.Both reaction systems produced vibrational population inversions in the multiple-collision regime. The experimental results demonstrate the ability to make significant variations in temporal gain profiles with minor modifications of reactant structure. A gain coefficient model was developed to calculate H20 vibrational state population ratios. The cyclohexane reaction, using a mixture of 700 mTorr of organic + 500 mTorr of acid, was found to have a population ratio 010/000 = 2.8 f 0.4 for times between 7.5 and 40 ps, with a peak gain signal at 15 ps. For the same pressure conditions, cyclooctane produced an average 010/000 = 1.1 f 0.2 over times from 50 to 1000 ps. Kinetic modeling was utilized to demonstrate the role of secondary reactions in providing a continuing source of H20 out to a few hundred microseconds. Limiting-case vibrational state population models were developed to illustrate the role of reaction dynamics and collisional quenching in determining population inversions.

12) Pikaev, A. K.; Kabakchi, S. A.; Zansdrhova, A. A. Furaday Discuss. (13) Anderson, R. F.; Vojnovic, B.; Michael, B. D. Radial. Phys. Chem. (14) Hu, H.; Schuler, R. H. To be published.Time-resolved diode laser infrared absorptionlgain spectroscopy was used to investigate vibrational energy disposal in H20 produced in the reaction of OH with cyclooctane. Penistant population inversions under multipleallision conditions were observed while probing transitions between the 0 0 0 1 0 , 0 1 0 2 0 , and 010-100 vibrational states of H20. An equilibrated rotational temperature was determined to be 500 f 200 K for typical reaction conditions.

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