Reactions of Highly Excited Molecules: From Supercollisions to Super-reactions?

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Amy Mullin of Boston University is supported by the Experimental Physical Chemistry Program to carry out studies aimed at elucidating the behavior and underlying principles that govern collisional and reactive processes of highly excited polyatomic molecules in the gas phase. Experimental studies will use pulsed UV nanosecond absorption, followed by rapid radiationless decay, to prepare highly vibrationally excited benzene-like molecules with internal energies ranging from 15,000 to 45,000 wavenumbers. High-resolution transient infrared absorption probing will be employed to monitor energy gain in collision partners or the appearance of reaction products. Project plans are to (1) investigate the energy dependence of collisional relaxation in excited azulene, (2) discover how internal energy content in relatively small excited molecules such as carbon disulfide influences collisional quenching dynamics, (3) explore how electrostatic interactions influence collisional relaxation of high-energy molecules by measuring energy gain in ammonia, (4) investigate the role of internal energy on hydrogen and deuterium abstraction reactions of high-energy molecules, (5) determine the ways in which exchange reactions of high-energy molecules compete with collisional energy transfer in water and deuterated water baths, and (6) perform classical trajectory calculations to aid in interpreting the experimental findings. Activated molecules play important roles in chemistry and biochemistry at almost every level. Molecules containing large amounts of energy are usually the most reactive species and hence are among the most important for determining the chemistry of thermal environments. This situation is especially true for high temperature processes involved in atmospheric, plasma, and combustion chemistry. The fundamental insights to be gained in this research may lead to cleaner, more efficient, and safer applications in these areas. Along with the education of graduate students, this project gives undergraduates and high school students important opportunities to participate directly in the state-of-the-art scientific research.