Energy dependence of collisional energy removal from vibrationally excited T(1) pyrazine

Date
1992
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Volume Title
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Abstract

In 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 $\sim3500cm\sp{-1}$ range of energy contents studied. At ET\sb1⟩ 2000 cm\sp−1, all buffers remove 5 to 10 cm\sp−1 per collision; at $\sim5500cm\sp{-1}$, the deduced energy removal rates per collision are $\sim55cm\sp{-1}$ 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.

Description
Degree
Doctor of Philosophy
Type
Thesis
Keywords
Physical chemistry, Molecular physics
Citation

Bevilacqua, Thomas Joseph. "Energy dependence of collisional energy removal from vibrationally excited T(1) pyrazine." (1992) Diss., Rice University. https://hdl.handle.net/1911/16526.

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