Weisman, R. Bruce2009-06-042009-06-041992Bevilacqua, Thomas Joseph. "Energy dependence of collisional energy removal from vibrationally excited T(1) pyrazine." (1992) Diss., Rice University. <a href="https://hdl.handle.net/1911/16526">https://hdl.handle.net/1911/16526</a>.https://hdl.handle.net/1911/16526In the first application of a new method for determining this information, rates of collisional vibrational energy removal have been measured for the T$\sb1$ state of pyrazine with vibrational energy contents ranging from 2000 to 5500 cm$\sp{-1}$. This method is the first to enable the measurement of energy removal from electronically excited states in the energy regime above that of well-separated vibrational states. It is also the first method applicable to excited triplet states in any energy regime. Energized T$\sb1$ pyrazine is formed through intersystem crossing from various laser-excited vibronic levels of the S$\sb1$ electronic state. Triplet-triplet transient absorption spectrometry is then used to monitor the T$\sb1$ decay kinetics under various collisional conditions. The new method of analyzing these kinetic data, based on the known variation of T$\sb1$ pyrazine's nonradiative decay rate with vibrational energy, allows the extraction of the rate of vibrational energy removal by the collision partners as a function of pyrazine vibrational energy. The key feature of the results is an approximately tenfold increase in the energy removed per collision within the $\sim$3500 cm$\sp{-1}$ range of energy contents studied. At $\langle$ ET$\sb1\rangle$ $\approx$ 2000 cm$\sp{-1}$, all buffers remove 5 to 10 cm$\sp{-1}$ per collision; at $\sim$5500 cm$\sp{-1}$, the deduced energy removal rates per collision are $\sim$55 cm$\sp{-1}$ for helium, 175 cm$\sp{-1}$ for argon, 160 cm$\sp{-1}$ for H$\sb2$, 530 cm$\sp{-1}$ for SF$\sb6$, and 360 cm$\sp{-1}$ for pyrazine. This increase, which is significantly steeper than found for vibrationally hot ground state molecules at higher energy contents, may be related to differences in the electronic characters of the molecules studied or in the regime of vibrational state densities investigated. The development of this new method for measuring energy removal rates and the intriguing results found with it should serve to stimulate further theoretical and experimental research into collisional relaxation of electronically excited states.130 p.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Physical chemistryMolecular physicsThesisThesis E.E. 1992 Bevilacqua