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Dynamics of Chemical Reactions and Photochemical Processes

Dynamics of Chemical Reactions and Photochemical Processes. Yuan T. Lee Academia Sinica, Taipei, Taiwan. m 4, u 4. m 1, u 1. m 2, u 2. m 3, u 3. M = m 1 + m 2 = m 3 + m 4. m 1 u 1 = m 2 u 2 or m 2 / m 1 = u 1 / u 2. m 3 u 3 = m 4 u 4 or m 4 / m 3 = u 3 / u 4. C 2 H 5 NO 2 ≠.

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Dynamics of Chemical Reactions and Photochemical Processes

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  1. Dynamics of Chemical Reactions and Photochemical Processes Yuan T. Lee Academia Sinica, Taipei, Taiwan

  2. m4, u4 m1, u1 m2, u2 m3, u3 M=m1+m2=m3+m4 m1u1 =m2u2 or m2 /m1 =u1 /u2 m3u3=m4u4 orm4 /m3=u3 /u4

  3. C2H5NO2≠ HONO + CH2=CH2

  4. C2H5NO2≠ C2H5 + NO2

  5. Δ HCN +HONO + NO2 + N2O + H2CO + ‧ ‧ ‧ ‧ ‧ ‧ ‧ ‧ ‧ ‧ N2 + CO + H2O Questions 1. Dissociation Mechanism Unimolecular vs. biomolecular Primary and secondary dissociations 2.Dissociation Dynamics Modes of Energy Release X. Zhao E. Hintsa Hexahydro-1,3,5-trinitro-1,3,5-triazineRDX

  6. 3CO + 3H2O + 3N2 High Temperature Combustion Concerted Steps HCN + HONO (3×) CH2=N-NO2 N2O + H2CO RDX

  7. Quantum chemistry is developing in at least two directions. First, very large systems can now be studied using conventional methods, namely Hartree-Fock theory, density functional theory, and second-order perturbation theory. Structural optimizations including all geometrical degrees of freedom can now be completed for molecules with as many as 200 atoms.   Frozen geometry computations (usually not very useful) can be carried out for systems of 1000 atoms. This work opens up a vast new expanse of chemistry for theoretical studies. F. Schaefer

  8. Secondly, more and more rigorous new methods are emerging every year. These can be applied to smaller systems (perhaps up to the size of benzene) to yield what I call sub-chemical accuracy, reliability to 0.5 kcal/mole or better.  As you know well, such energetic quantities are critical to combustion and environmental studies and in some cases are very difficult to determine from experiment. Among the newer methods, coupled cluster theory with all single, double, triple, and quadruple excitations, CCSDTQ, is becoming a viable technique. F. Schaefer

  9. Especially important is the development of methods that explicitly include the inter-electronic coordinates R12.  These ideas have been around since the famous work of Hylleraas on the He atom in 1928.  However, it is only in the past five years that such methods have become useful for studying chemical systems.  Also encouraging is that most of the work in this R12 area is being done by young people, for example Wim Klopper (Karlsruhe), Fred Manby (Bristol), and Edward Valeev (Virginia Tech). F. Schaefer

  10. Ortho-Benzyne decomposition, Simmonett, Allen, and Schaefer (2006) CCSD(T) / cc-pVTZ transition state geometry

  11. Fully optimized geometries of 2’-deoxyriboadenosine 2’-deoxyribothymidine pair. J. Gu, Y. Xie, and H.F. Schaefer (2006)

  12. m4, u4 m1, u1 m2, u2 m3, u3 M=m1+m2=m3+m4 m1u1 =m2u2 or m2 /m1 =u1 /u2 m3u3=m4u4 orm4 /m3=u3 /u4

  13. mv=F△t=ma△t =Constant=P E= m E-1

  14. I.C. + CH3 193nm + H Toluene

  15. Photodissociation of C6H5CD3 @ 193 nm J. Am. Chem. Soc. 124, 4068 ( 2002 ) Velocity Axis m/e 15 CH3 m/e 16 CH2D m/e 17 CHD2 m/e 18 CD3 Mass Axis m/e 76 m/e 77 C6H5 m/e 78 C6H4D m/e 79 C6H3D2 m/e 80 C6H2D3 m/e 93 C6H5CD2 m/e 94 C6H4DCD2 m/e 95 C6H5CD3 m/e 96

  16. Energy diagram of isomers and photoproducts of C6H5CH3 C6H5CH2 + H DFT CCSD

  17. Early Discovery: Ring Permutation (in 1960s) hn New Observation: Seven-Membered Ring Pathway C6H5 + CD3 C6H4D+CD2H Also C6H3D2+CDH2 C6H2D3+CH3 C6H5+CD3 hn193nm C6H5 + 13CH3 hn193nm C513CH5+CH3 Also C6H5+13CH3 Comparison of Photoisomerization Mechanisms

  18. hn H, NH2 193nm CH3 H, CH3 hn 193nm NH2 C6NH7

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