A new method for computing anharmonic rovibrational densities of states of interstellar and atmospheric clusters at arbitrary angular momenta

Sarah Windsor (2009). A new method for computing anharmonic rovibrational densities of states of interstellar and atmospheric clusters at arbitrary angular momenta PhD Thesis, School of Chemistry and Molecular Biosciences, The University of Queensland.

       
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Author Sarah Windsor
Thesis Title A new method for computing anharmonic rovibrational densities of states of interstellar and atmospheric clusters at arbitrary angular momenta
School, Centre or Institute School of Chemistry and Molecular Biosciences
Institution The University of Queensland
Publication date 2009-04
Thesis type PhD Thesis
Supervisor Prof Sean Smith
Dr Marlies Hankel
Total pages 203
Total colour pages 31
Total black and white pages 172
Subjects 06 Biological Sciences
Abstract/Summary A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.
Keyword interstellar, atmospheric, classical, density of states, metastable, partition function,
equilibrium constant, rate constant, lifetime
Additional Notes 115, 118-119, 128-130, 132, 134-138, 141, 143-150, 156-158, 160, 162, 164, 167-169, 172

 
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